Linux Filesystem Hierarchy

Table of Contents
Source and pre-formatted versions available
1. Linux Filesystem Hierarchy
    1.1. Foreward
    1.2. The Root Directory
    1.3. /bin
    1.4. /boot
    1.5. /dev
    1.6. /etc
    1.7. /home
    1.8. /initrd
    1.9. /lib
    1.10. /lost+found
    1.11. /media
    1.12. /mnt
    1.13. /opt
    1.14. /proc
    1.15. /root
    1.16. /sbin
    1.17. /usr
    1.18. /var
    1.19. /srv
    1.20. /tmp
   
   
Glossary
A. UNIX System V Signals
B. Sources
C. About the Author
D. Contributors
E. Disclaimer
F. Donations
G. Feedback
H. GNU Free Documentation License
    H.1. PREAMBLE
    H.2. APPLICABILITY AND DEFINITIONS
    H.3. VERBATIM COPYING
    H.4. COPYING IN QUANTITY
    H.5. MODIFICATIONS
    H.6. COMBINING DOCUMENTS
    H.7. COLLECTIONS OF DOCUMENTS
    H.8. AGGREGATION WITH INDEPENDENT WORKS
    H.9. TRANSLATION
    H.10. TERMINATION
    H.11. FUTURE REVISIONS OF THIS LICENSE
    H.12. ADDENDUM: How to use this License for your documents
   
   

-----------------------------------------------------------------------------
Source and pre-formatted versions available

The source code and other machine readable formats of this book can be found
on the Internet at the Linux Documentation Project home page [http://
www.tldp.org] http://www.tldp.org The latest version of this document can be
found at [http://cvsview.tldp.org/index.cgi/LDP/guide/docbook/
Linux-Filesystem-Hierarchy/]  http://cvsview.tldp.org/index.cgi/LDP/guide/
docbook/Linux-Filesystem-Hierarchy/
-----------------------------------------------------------------------------

Chapter 1. Linux Filesystem Hierarchy

1.1. Foreward

When migrating from another operating system such as Microsoft Windows to
another; one thing that will profoundly affect the end user greatly will be
the differences between the filesystems.

What are filesystems?

A filesystem is the methods and data structures that an operating system uses
to keep track of files on a disk or partition; that is, the way the files are
organized on the disk. The word is also used to refer to a partition or disk
that is used to store the files or the type of the filesystem. Thus, one
might say I have two filesystems meaning one has two partitions on which one
stores files, or that one is using the extended filesystem, meaning the type
of the filesystem.

The difference between a disk or partition and the filesystem it contains is
important. A few programs (including, reasonably enough, programs that create
filesystems) operate directly on the raw sectors of a disk or partition; if
there is an existing file system there it will be destroyed or seriously
corrupted. Most programs operate on a filesystem, and therefore won't work on
a partition that doesn't contain one (or that contains one of the wrong
type).

 Before a partition or disk can be used as a filesystem, it needs to be
initialized, and the bookkeeping data structures need to be written to the
disk. This process is called making a filesystem.

Most UNIX filesystem types have a similar general structure, although the
exact details vary quite a bit. The central concepts are superblock, inode, 
data block, directory block, and indirection block. The superblock contains
information about the filesystem as a whole, such as its size (the exact
information here depends on the filesystem). An inode contains all
information about a file, except its name. The name is stored in the
directory, together with the number of the inode. A directory entry consists
of a filename and the number of the inode which represents the file. The
inode contains the numbers of several data blocks, which are used to store
the data in the file. There is space only for a few data block numbers in the
inode, however, and if more are needed, more space for pointers to the data
blocks is allocated dynamically. These dynamically allocated blocks are
indirect blocks; the name indicates that in order to find the data block, one
has to find its number in the indirect block first.

 Like UNIX, Linux chooses to have a single hierarchical directory structure.
Everything starts from the root directory, represented by /, and then expands
into sub-directories instead of having so-called 'drives'. In the Windows
environment, one may put one's files almost anywhere: on C drive, D drive, E
drive etc. Such a file system is called a hierarchical structure and is
managed by the programs themselves (program directories), not by the
operating system. On the other hand, Linux sorts directories descending from
the root directory / according to their importance to the boot process.

 If you're wondering why Linux uses the frontslash / instead of the backslash
\ as in Windows it's because it's simply following the UNIX tradition. Linux,
like Unix also chooses to be case sensitive. What this means is that the
case, whether in capitals or not, of the characters becomes very important.
So this is not the same as THIS. This feature accounts for a fairly large
proportion of problems for new users especially during file transfer
operations whether it may be via removable disk media such as floppy disk or
over the wire by way of FTP.

 The filesystem order is specific to the function of a file and not to its
program context (the majority of Linux filesystems are 'Second Extended File
Systems', short 'EXT2' (aka 'ext2fs' or 'extfs2') or are themselves subsets
of this filesystem such as ext3 and Reiserfs). It is within this filesystem
that the operating system determines into which directories programs store
their files.

 If you install a program in Windows, it usually stores most of its files in
its own directory structure. A help file for instance may be in C:\Program
Files\[program name]\ or in C:\Program Files\[program-name]\help or in C:\
Program Files\[program -name]\humpty\dumpty\doo. In Linux, programs put their
documentation into /usr/share/doc/[program-name], man(ual) pages into /usr/
share/man/man[1-9] and info pages into /usr/share/info. They are merged into
and with the system hierarchy.

 As all Linux users know, unless you mount a partition or a device, the
system does not know of the existence of that partition or device. This might
not appear to be the easiest way to provide access to your partitions or
devices, however it offers the advantage of far greater flexibility when
compared to other operating systems. This kind of layout, known as the
unified filesystem, does offer several advantages over the approach that
Windows uses. Let's take the example of the /usr directory. This
sub-directory of the root directory contains most of the system executables.
With the Linux filesystem, you can choose to mount it off another partition
or even off another machine over the network using an innumerable set of
protocols such as NFS (Sun), Coda (CMU) or AFS (IBM). The underlying system
will not and need not know the difference. The presence of the /usr directory
is completely transparent. It appears to be a local directory that is part of
the local directory structure.

Compliance requires that:
 +---------+-----------------+-------------+                                 
 |         | shareable       | unshareable |                                 
 +---------+-----------------+-------------+                                 
 |static   | /usr            | /etc        |                                 
 |         | /opt            | /boot       |                                 
 +---------+-----------------+-------------+                                 
 |variable | /var/mail       | /var/run    |                                 
 |         | /var/spool/news | /var/lock   |                                 
 +---------+-----------------+-------------+                                 
                                                                             
 "Shareable" files are defined as those that can be stored on one host and   
 used on others. "Unshareable" files are those that are not shareable. For   
 example, the files in user home directories are shareable whereas device    
 lock files are not. "Static" files include binaries, libraries,             
 documentation files and other files that do not change without system       
 administrator intervention. "Variable" files are defined as files that      
 are not static.                                                             
                                                                             

 Another reason for this unified filesystem is that Linux caches a lot of
disk accesses using system memory while it is running to accelerate these
processes. It is therefore vitally important that these buffers are flushed
(get their content written to disk), before the system closes down. Otherwise
files are left in an undetermined state which is of course a very bad thing.
Flushing is achieved by 'unmounting' the partitions during proper system
shutdown. In other words, don't switch your system off while it's running! 
You may get away with it quite often, since the Linux file system is very
robust, but you may also wreak havoc upon important files. Just hit
ctrl-alt-del or use the proper commands (e.g. shutdown, poweroff, init 0).
This will shut down the system in a decent way which will thus, guarantee the
integrity of your files.

 Many of us in the Linux community have come to take for granted the
existence of excellent books and documents about Linux, an example being
those produced by the Linux Documentation Project. We are used to having
various packages taken from different sources such as Linux FTP sites and
distribution CD-ROMs integrate together smoothly. We have come to accept that
we all know where critical files like mount can be found on any machine
running Linux. We also take for granted CD-ROM based distributions that can
be run directly from the CD and which consume only a small amount of physical
hard disk or a RAM disk for some variable files like /etc/passwd, etc. This
has not always been the case.

 During the adolescent years of Linux during the early to mid-90s each
distributor had his own favorite scheme for locating files in the directory
hierarchy. Unfortunately, this caused many problems. The Linux File System
Structure is a document, which was created to help end this anarchy. Often
the group, which creates this document or the document itself, is referred to
as the FSSTND. This is short for file system standard". This document has
helped to standardize the layout of file systems on Linux systems everywhere.
Since the original release of the standard, most distributors have adopted it
in whole or in part, much to the benefit of all Linux users.

Since the first draft of the standard, the FSSTND project has been
coordinated by Daniel Quinlan and development of this standard has been
through consensus by a group of developers and Linux enthusiasts. The FSSTND
group set out to accomplish a number of specific goals. The first goal was to
solve a number of problems that existed with the current distributions at the
time. Back then, it was not possible to have a shareable /usr partition,
there was no clear distinction between /bin and /usr/bin, it was not possible
to set up a diskless workstation, and there was just general confusion about
what files went where. The second goal was to ensure the continuation of some
reasonable compatibility with the de-facto standards already in use in Linux
and other UNIX-like operating systems. Finally, the standard had to gain
widespread approval by the developers, distributors, and users within the
Linux community. Without such support, the standard would be pointless,
becoming just another way of laying out the file system.

Fortunately, the FSSTND has succeeded though there are also some goals that
the FSSTND project did not set out to achieve. The FSSTND does not try to
emulate the scheme of any specific commercial UNIX operating system (e.g.
SunOS, AIX, etc.) Furthermore, for many of the files covered by the FSSTND,
the standard does not dictate whether the files should be present, merely
where the files should be if they are present. Finally, for most files, the
FSSTND does not attempt to dictate the format of the contents of the files.
(There are some specific exceptions when several different packages may need
to know the file formats to work together properly. For example, lock files
that contain the process ID of the process holding the lock.) The overall
objective was to establish the location where common files could be found, if
they existed on a particular machine. The FSSTND project began in early
August 1993. Since then, there have been a number of public revisions of this
document. The latest, v2.3 was released on January 29, 2004.

If you're asking "What's the purpose of all this? Well, the answer depends on
who you are. If you are a Linux user, and you don't administrate your own
system then the FSSTND ensures that you will be able to find programs where
you'd expect them to be if you've already had experience on another Linux
machine. It also ensures that any documentation you may have makes sense.
Furthermore, if you've already had some experience with Unix before, then the
FSSTND shouldn't be too different from what you're currently using, with a
few exceptions. Perhaps the most important thing is that the development of a
standard brings Linux to a level of maturity authors and commercial
application developers feel they can support.

If you administer your own machine then you gain all the benefits of the
FSSTND mentioned above. You may also feel more secure in the ability of
others to provide support for you, should you have a problem. Furthermore,
periodic upgrades to your system are theoretically easier. Since there is an
agreed-upon standard for the locations of files, package maintainers can
provide instructions for upgrading that will not leave extra, older files
lying around your system inhabiting valuable disk space. The FSSTND also
means that there is more support from those providing source code packages
for you to compile and install yourself. The provider knows, for example,
where the executable for sed is to be found on a Linux machine and can use
that in his installation scripts or Makefiles.

If you run a large network, the FSSTND may ease many of your NFS headaches,
since it specifically addresses the problems which formerly made shared
implementations of /usr impractical. If you are a distributor, then you will
be affected most by the Linux FSSTND. You may have to do a little extra work
to make sure that your distribution is FSSTND-compliant, but your users (and
hence your business) will gain by it. If your system is compliant, third
party add-on packages (and possibly your own) will integrate smoothly with
your system. Your users will, of course, gain all the benefits listed above,
and many of your support headaches will be eased. You will benefit from all
the discussion and thought that has been put into the FSSTND and avoid many
of the pitfalls involved in designing a filesystem structure yourself. If you
adhere to the FSSTND, you will also be able to take advantage of various
features that the FSSTND was designed around. For example, the FSSTND makes
"live" CD-ROMs containing everything except some of the files in the / and /
var directories possible. If you write documentation for Linux, the FSSTND
makes it much easier to do so, which makes sense to the Linux community. You
no longer need to worry about the specific location of lock files on one
distribution versus another, nor are you forced to write documentation that
is only useful to the users of a specific distribution. The FSSTND is at
least partly responsible for the recent explosion of Linux books being
published.

If you are a developer, the existence of the FSSTND greatly eases the
possibility for potential problems. You can know where important system
binaries are found, so you can use them from inside your programs or your
shell scripts. Supporting users is also greatly eased, since you don't have
to worry about things like the location of these binaries when resolving
support issues. If you are the developer of a program that needs to integrate
with the rest of the system, the FSSTND ensures that you can be certain of
the steps to meet this end. For example, applications such as kermit, which
access the serial ports, need to know they can achieve exclusive access to
the TTY device. The FSSTND specifies a common method of doing this so that
all compliant applications can work together. That way you can concentrate on
making more great software for Linux instead of worrying about how to detect
and deal with the differences in flavors of Linux. The widespread acceptance
of the FSSTND by the Linux community has been crucial to the success of both
the standard and operating system. Nearly every modern distribution conforms
to the Linux FSSTND. If your implementation isn't at least partially FSSTND
compliant, then it is probably either very old or you built it yourself. The
FSSTND itself contains a list of some of the distributions that aim to
conform to the FSSTND. However, there are some distributions that are known
to cut some corners in their implementation of FSSTND.

By no means does this mean that the standard itself is complete. There are
still unresolved issues such as the organization of architecture-independent
scripts and data files /usr/share. Up until now, the i386 has been the
primary platform for Linux, so the need for standardization of such files was
non-existent.

The rapid progress in porting Linux to other architectures (MC680x0, Alpha,
MIPS, PowerPC) suggests that this issue will soon need to be dealt with.
Another issue that is under some discussion is the creation of an /opt
directory as in SVR4. The goal for such a directory would be to provide a
location for large commercial or third party packages to install themselves
without worrying about the requirements made by FSSTND for the other
directory hierarchies. The FSSTND provides the Linux community with an
excellent reference document and has proven to be an important factor in the
maturation of Linux. As Linux continues to evolve, so will the FSSTND.

Now, that we have seen how things should be, let's take a look at the real
world. As you will see, the implementation of this concept on Linux isn't
perfect and since Linux has always attracted individualists who tend to be
fairly opinionated, it has been a bone of contention among users for instance
which directories certain files should be put into. With the arrival of
different distributions, anarchy has once again descended upon us. Some
distributions put mount directories for external media into the / directory,
others into /mnt. Red Hat based distributions feature the /etc/sysconfig
sub-hierarchy for configuration files concerning input and network devices.
Other distributions do not have this directory at all and put the appropriate
files elsewhere or even use completely different mechanisms to do the same
thing. Some distributions put KDE into /opt/, others into /usr.

But even within a given file system hierarchy, there are inconsistencies. For
example, even though this was never the intention of the XFree86 group,
XFree86 does indeed have its own directory hierarchy.

These problems don't manifest themselves as long as you compile programs
yourself. You can adapt configure scripts or Makefiles to your system's
configuration or to your preference. It's a different story if you install
pre-compiled packages like RPMs though. Often these are not adaptable from
one file system hierarchy to another. What's worse: some RPMs might even
create their own hierarchy. If you, say, install a KDE RPM from the SuSE
Linux distribution on your Mandrake system, the binary will be put into /opt/
kde2/bin. And thus it won't work, because Mandrake expects it to be in /usr/
bin. There are of course ways to circumvent this problem but the current
situation is clearly untenable. Thus, all the leading Linux distributors have
joined the Linux Standard Base project, which is attempting to create a
common standard for Linux distributions. This isn't easy, since changing the
file system hierarchy means a lot of work for distributors so every
distributor tries to push a standard which will allow them to keep as much of
their own hierarchy as possible. The LSB will also encompass the proposals
made by the Filesystem Hierarchy Standard project (FHS, former FSSTND).
-----------------------------------------------------------------------------

1.2. The Root Directory

  To comply with the FSSTND the following directories, or symbolic links to
directories, are required in /.

 
       /bin       Essential command binaries                                 
       /boot      Static files of the boot loader                            
       /dev       Device files                                               
       /etc       Host-specific system configuration                         
       /lib       Essential shared libraries and kernel modules              
       /media     Mount point for removeable media                           
       /mnt       Mount point for mounting a filesystem temporarily          
       /opt       Add-on application software packages                       
       /sbin      Essential system binaries                                  
       /srv       Data for services provided by this system                  
       /tmp       Temporary files                                            
       /usr       Secondary hierarchy                                        
       /var       Variable data                                              
                                                                             

The following directories, or symbolic links to directories, must be in /, if
the corresponding subsystem is installed:

 
     / -- the root directory                                                 
     /home User home directories (optional)                                  
     /lib<qual> Alternate format essential shared libraries                  
                      (optional)                                             
     /root Home directory for the root user (optional)                       
                                                                             

  Each directory listed above is described in detail in separate subsections
further on in this document.

  The reference system will be based upon Debian 3.0r0 (Woody), 2.4.18 kernel
configured to a Redhat kernel-2.4.18-i686.config file.

 

Hardware
     
   
      + Intel Celeron 766 Processor
       
      + MSI MS-6309 V.2.0 Mainboard
       
      + 512MB PQI PC133 SDRAM
       
      + 16x Lite-On LTD-165H DVD-ROM
       
      + 40x24x10 Sony CRX175A1 CD-RW
       
      + NVIDIA RIVA 32MB TNT2 M64
       
      + D-Link DFE-530TX 10/100 NIC
       
      + Realtek RTL8029(AS) 10 NIC
       
      + Lucent Mars2 Linmodem
       
      + C-Media CMI8738 PCI Audio Device
       
      + Miro DC-30 VIVO
       
      + Aopen KF-45A Miditower Case
       
      + Acer Accufeel Keyboard
       
      + Genius Netscroll+ Mouse
       
      + Compaq MV500 Presario Monitor
       
   
Software
     
   
      + Windows XP on /dev/hda1
       
      + FreeBSD 4.2 on /dev/hda2
       
      + Redhat 8.0 on /dev/hda5
       
      + Debian 3.0r0 on /dev/hda6
       
      + Mandrake 9.1 on /dev/hda7
       
      + Swap partition on /dev/hda8
       
   

  As we all know Linux file system starts with /, the root directory. All
other directories are 'children' of this directory. The partition which the
root file system resides on is mounted first during boot and the system will
not boot if it doesn't find it. On our reference system, the root directory
contains the following sub-directories:

  bin/ dev/ home/ lost+found/ proc/ sbin/ usr/ cdrom/ opt/ vmlinuz boot/ etc/
lib/ mnt/ root/ tmp/ var/ dvd/ floppy/ initrd/ /tftpboot

  In days past it was also the home directory of 'root' but now he has been
given his own directory for reasons that will be explained further on in this
document.
-----------------------------------------------------------------------------

1.3. /bin

 Unlike /sbin, the bin directory contains several useful commands that are of
use to both the system administrator as well as non-privileged users. It
usually contains the shells like bash, csh, etc.... and commonly used
commands like cp, mv, rm, cat, ls. For this reason and in contrast to /usr/
bin, the binaries in this directory are considered to be essential. The
reason for this is that it contains essential system programs that must be
available even if only the partition containing / is mounted. This situation
may arise should you need to repair other partitions but have no access to
shared directories (ie. you are in single user mode and hence have no network
access). It also contains programs which boot scripts may depend on.

 Compliance to the FSSTND means that there are no subdirectories in /bin and
that the following commands, or symbolic links to commands, are located
there.

 
cat      Utility to concatenate files to standard output                      
chgrp    Utility to change file group ownership                               
chmod    Utility to change file access permissions                            
chown    Utility to change file owner and group                               
cp       Utility to copy files and directories                                
date     Utility to print or set the system data and time                     
dd       Utility to convert and copy a file                                   
df       Utility to report filesystem disk space usage                        
dmesg    Utility to print or control the kernel message buffer                
echo     Utility to display a line of text                                    
false    Utility to do nothing, unsuccessfully                                
hostname Utility to show or set the system's host name                        
kill     Utility to send signals to processes                                 
ln       Utility to make links between files                                  
login    Utility to begin a session on the system                             
ls       Utility to list directory contents                                   
mkdir    Utility to make directories                                          
mknod    Utility to make block or character special files                     
more     Utility to page through text                                         
mount    Utility to mount a filesystem                                        
mv       Utility to move/rename files                                         
ps       Utility to report process status                                     
pwd      Utility to print name of current working directory                   
rm       Utility to remove files or directories                               
rmdir    Utility to remove empty directories                                  
sed      The `sed' stream editor                                              
sh       The Bourne command shell                                             
stty     Utility to change and print terminal line settings                   
su       Utility to change user ID                                            
sync     Utility to flush filesystem buffers                                  
true     Utility to do nothing, successfully                                  
umount   Utility to unmount file systems                                      
uname    Utility to print system information                                  
                                                                              
If /bin/sh is not a true Bourne shell, it must be a hard or symbolic link to  
the real shell command.                                                       
                                                                              
The rationale behind this is because sh and bash mightn't necessarily behave  
in the same manner. The use of a symbolic link also allows users to easily    
see that /bin/sh is not a true Bourne shell.                                  
                                                                              
The [ and test commands must be placed together in either /bin or /usr/bin.   
                                                                              
The requirement for the [ and test commands to be included as binaries        
(even if implemented internally by the shell) is shared with the POSIX.2      
standard.                                                                     
                                                                              
The following programs, or symbolic links to programs, must be in /bin if the 
corresponding subsystem is installed:                                         
                                                                              
csh     The C shell (optional)                                                
ed      The `ed' editor (optional)                                            
tar     The tar archiving utility (optional)                                  
cpio    The cpio archiving utility (optional)                                 
gzip    The GNU compression utility (optional)                                
gunzip  The GNU uncompression utility (optional)                              
zcat    The GNU uncompression utility (optional)                              
netstat The network statistics utility (optional)                             
ping    The ICMP network test utility (optional)                              
                                                                              
If the gunzip and zcat programs exist, they must be symbolic or hard links to 
gzip. /bin/csh may be a symbolic link to /bin/tcsh or /usr/bin/tcsh.          
                                                                              
The tar, gzip and cpio commands have been added to make restoration of a      
system possible (provided that / is intact).                                  
                                                                              
Conversely, if no restoration from the root partition is ever expected,       
then these binaries might be omitted (e.g., a ROM chip root, mounting /usr    
through NFS). If restoration of a system is planned through the network,      
then ftp or tftp (along with everything necessary to get an ftp connection)   
must be available on the root partition.                                      
-----------------------------------------------------------------------------

1.4. /boot

This directory contains everything required for the boot process except for
configuration files not needed at boot time (the most notable of those being
those that belong to the GRUB boot-loader) and the map installer. Thus, the /
boot directory stores data that is used before the kernel begins executing
user-mode programs. This may include redundant (back-up) master boot records,
sector/system map files, the kernel and other important boot files and data
that is not directly edited by hand. Programs necessary to arrange for the
boot loader to be able to boot a file are placed in /sbin. Configuration
files for boot loaders are placed in /etc. The system kernel is located in
either / or /boot (or as under Debian in /boot but is actually a symbolically
linked at / in accordance with the FSSTND).

/boot/boot.0300
    Backup master boot record.
   
/boot/boot.b
    This is installed as the basic boot sector. In the case of most modern
    distributions it is actually a symbolic link to one of four files /boot/
    boot-bmp.b, /boot/boot-menu.b, /boot/boot-text.b, /boot/boot-compat.b
    which allow a user to change the boot-up schema so that it utilises a
    splash screen, a simple menu, a text based interface or a minimal boot
    loader to ensure compatibility respectively. In each case re-installation
    of lilo is necessary in order to complete the changes. To change the
    actual 'boot-logo' you can either use utilities such as fblogo or the
    more refined bootsplash.
   
/boot/chain.b
    Used to boot non-Linux operating systems.
   
/boot/config-kernel-version
    Installed kernel configuration. This file is most useful when compiling
    kernels on other systems or device modules. Below is a small sample of
    what the contents of the file looks like.
   
            CONFIG_X86=y                                                     
            CONFIG_MICROCODE=m                                               
            CONFIG_X86_MSR=m                                                 
            CONFIG_MATH_EMULATION=y                                          
            CONFIG_MTRR=y                                                    
            CONFIG_MODULES=y                                                 
            CONFIG_MODVERSIONS=y                                             
            CONFIG_SCSI_DEBUG=m                                              
            CONFIG_I2O=m                                                     
            CONFIG_ARCNET_ETH=y                                              
            CONFIG_FMV18X=m                                                  
            CONFIG_HPLAN_PLUS=m                                              
            CONFIG_ETH16I=m                                                  
            CONFIG_NE2000=m                                                  
            CONFIG_HISAX_HFC_PCI=y                                           
            CONFIG_ISDN_DRV_AVMB1_C4=m                                       
            CONFIG_USB_RIO500=m                                              
            CONFIG_QUOTA=y                                                   
            CONFIG_AUTOFS_FS=m                                               
            CONFIG_ADFS_FS=m                                                 
            CONFIG_AFFS_FS=m                                                 
            CONFIG_HFS_FS=m                                                  
            CONFIG_FAT_FS=y                                                  
            CONFIG_MSDOS_FS=y                                                
            CONFIG_UMSDOS_FS=m                                               
            CONFIG_FBCON_VGA=m                                               
            CONFIG_FONT_8x8=y                                                
            CONFIG_FONT_8x16=y                                               
            CONFIG_SOUND=m                                                   
            CONFIG_SOUND_CMPCI=m                                             
            CONFIG_AEDSP16=m                                                 
                                                                             
   
    As you can see, it's rather simplistic. The line begins with the
    configuration option and whether it's configured as part of the kernel,
    as a module or not at all. Lines beginning with a # symbol are comments
    and are not interpreted during processing.
   
/boot/os2_d.b
    Used to boot to the 0S/2 operating system.
   
/boot/map
    Contains the location of the kernel.
   
/boot/vmlinuz, /boot/vmlinuz-kernel-version
    Normally the kernel or symbolic link to the kernel.
   
/boot/grub
    This subdirectory contains the GRUB configuration files including boot-up
    images and sounds. GRUB is the GNU GRand Unified Bootloader, a project
    which intends to solve all bootup problems once and for all. One of the
    most interesting features, is that you don't have to install a new
    partition or kernel, you can change all parameters at boot time via the
    GRUB Console, since it knows about the filesystems.
   
/boot/grub/device.map
    Maps devices in /dev to those used by grub. For example, (/dev/fd0) is
    represented by /dev/fd0 and (hd0, 4) is referenced by /dev/hda5.
   
/boot/grub/grub.conf, /boot/grub/menu.lst
    Grub configuration file.
   
/boot/grub/messages
    Grub boot-up welcome message.
   
/boot/grub/splash.xpm.gz
    Grub boot-up background image.
   

-----------------------------------------------------------------------------
1.5. /dev

/dev is the location of special or device files. It is a very interesting
directory that highlights one important aspect of the Linux filesystem -
everything is a file or a directory. Look through this directory and you
should hopefully see hda1, hda2 etc.... which represent the various
partitions on the first master drive of the system. /dev/cdrom and /dev/fd0
represent your CD-ROM drive and your floppy drive. This may seem strange but
it will make sense if you compare the characteristics of files to that of
your hardware. Both can be read from and written to. Take /dev/dsp, for
instance. This file represents your speaker device. Any data written to this
file will be re-directed to your speaker. If you try 'cat /boot/vmlinuz > /
dev/dsp' (on a properly configured system) you should hear some sound on the
speaker. That's the sound of your kernel! A file sent to /dev/lp0 gets
printed. Sending data to and reading from /dev/ttyS0 will allow you to
communicate with a device attached there - for instance, your modem.

The majority of devices are either block or character devices; however other
types of devices exist and can be created. In general, 'block devices' are
devices that store or hold data, 'character devices' can be thought of as
devices that transmit or transfer data. For example, diskette drives, hard
drives and CD-ROM drives are all block devices while serial ports, mice and
parallel printer ports are all character devices. There is a naming scheme of
sorts but in the vast majority of cases these are completely illogical.

 
total 724                                                                        
lrwxrwxrwx    1 root     root           13 Sep 28 18:06 MAKEDEV -> /sbin/MAKEDEV 
crw-rw----    1 root     audio     14,  14 Oct  7 16:26 admmidi0                 
crw-rw----    1 root     audio     14,  30 Oct  7 16:26 admmidi1                 
lrwxrwxrwx    1 root     root           11 Oct  7 16:26 amidi -> /dev/amidi0     
crw-rw----    1 root     audio     14,  13 Oct  7 16:26 amidi0                   
crw-rw----    1 root     audio     14,  29 Oct  7 16:26 amidi1                   
crw-rw----    1 root     audio     14,  11 Oct  7 16:26 amixer0                  
crw-rw----    1 root     audio     14,  27 Oct  7 16:26 amixer1                  
drwxr-xr-x    2 root     root         4096 Sep 28 18:05 ataraid                  
lrwxrwxrwx    1 root     root           11 Oct  7 16:26 audio -> /dev/audio0     
crw-rw----    1 root     audio     14,   4 Oct  7 16:26 audio0                   
crw-rw----    1 root     audio     14,  20 Oct  7 16:26 audio1                   
crw-rw----    1 root     audio     14,   7 Mar 15  2002 audioctl                 
lrwxrwxrwx    1 root     root            9 Oct 14 22:51 cdrom -> /dev/scd1       
lrwxrwxrwx    1 root     root            9 Oct 14 22:52 cdrom1 -> /dev/scd0      
crw-------    1 root     tty        5,   1 Jan 19 20:47 console                  
lrwxrwxrwx    1 root     root           11 Sep 28 18:06 core -> /proc/kcore      
crw-rw----    1 root     audio     14,  10 Oct  7 16:26 dmfm0                    
crw-rw----    1 root     audio     14,  26 Oct  7 16:26 dmfm1                    
crw-rw----    1 root     audio     14,   9 Oct  7 16:26 dmmidi0                  
crw-rw----    1 root     audio     14,  25 Oct  7 16:26 dmmidi1                  
lrwxrwxrwx    1 root     root            9 Oct  7 16:26 dsp -> /dev/dsp0         
crw-rw----    1 root     audio     14,   3 Oct  7 16:26 dsp0                     
crw-rw----    1 root     audio     14,  19 Oct  7 16:26 dsp1                     
crw--w----    1 root     video     29,   0 Mar 15  2002 fb0                      
crw--w----    1 root     video     29,   1 Mar 15  2002 fb0autodetect            
crw--w----    1 root     video     29,   0 Mar 15  2002 fb0current               
crw--w----    1 root     video     29,  32 Mar 15  2002 fb1                      
crw--w----    1 root     video     29,  33 Mar 15  2002 fb1autodetect            
crw--w----    1 root     video     29,  32 Mar 15  2002 fb1current               
lrwxrwxrwx    1 root     root           13 Sep 28 18:05 fd -> /proc/self/fd      
brw-rw----    1 root     floppy     2,   0 Mar 15  2002 fd0                      
brw-rw----    1 root     floppy     2,   1 Mar 15  2002 fd1                      
crw--w--w-    1 root     root       1,   7 Sep 28 18:06 full                     
brw-rw----    1 root     disk       3,   0 Mar 15  2002 hda                      
brw-rw----    1 root     disk       3,  64 Mar 15  2002 hdb                      
brw-rw----    1 root     disk      22,   0 Mar 15  2002 hdc                      
brw-rw----    1 root     disk      22,  64 Mar 15  2002 hdd                      
drwxr-xr-x    2 root     root        12288 Sep 28 18:05 ida                      
prw-------    1 root     root            0 Jan 19 20:46 initctl                  
brw-rw----    1 root     disk       1, 250 Mar 15  2002 initrd                   
drwxr-xr-x    2 root     root         4096 Sep 28 18:05 input                    
crw-rw----    1 root     dialout   45, 128 Mar 15  2002 ippp0                    
crw-rw----    1 root     dialout   45,   0 Mar 15  2002 isdn0                    
crw-rw----    1 root     dialout   45,  64 Mar 15  2002 isdnctrl0                
crw-rw----    1 root     dialout   45, 255 Mar 15  2002 isdninfo                 
crw-------    1 root     root      10,   4 Mar 15  2002 jbm                      
crw-r-----    1 root     kmem       1,   2 Sep 28 18:06 kmem                     
brw-rw----    1 root     cdrom     24,   0 Mar 15  2002 lmscd                    
crw-------    1 root     root      10,   0 Mar 15  2002 logibm                   
brw-rw----    1 root     disk       7,   0 Sep 28 18:06 loop0                    
brw-rw----    1 root     disk       7,   1 Sep 28 18:06 loop1                    
crw-rw----    1 root     lp         6,   0 Mar 15  2002 lp0                      
crw-rw----    1 root     lp         6,   1 Mar 15  2002 lp1                      
crw-rw----    1 root     lp         6,   2 Mar 15  2002 lp2                      
crw-r-----    1 root     kmem       1,   1 Sep 28 18:06 mem                      
lrwxrwxrwx    1 root     root           10 Oct  7 16:26 midi -> /dev/midi0       
crw-rw----    1 root     audio     14,   2 Oct  7 16:26 midi0                    
crw-rw----    1 root     audio     14,  18 Oct  7 16:26 midi1                    
lrwxrwxrwx    1 root     root           11 Oct  7 16:26 mixer -> /dev/mixer0     
crw-rw-rw-    1 root     root      14,   0 Nov 11 16:22 mixer0                   
crw-rw----    1 root     audio     14,  16 Oct  7 16:26 mixer1                   
lrwxrwxrwx    1 root     root           11 Oct  7 06:50 modem -> /dev/ttyLT0     
crw-rw----    1 root     audio     31,   0 Mar 15  2002 mpu401data               
crw-rw----    1 root     audio     31,   1 Mar 15  2002 mpu401stat               
crw-rw----    1 root     audio     14,   8 Oct  7 16:26 music                    
crw-rw-rw-    1 root     root       1,   3 Sep 28 18:06 null                     
crw-rw-rw-    1 root     root     195,   0 Jan  6 03:03 nvidia0                  
crw-rw-rw-    1 root     root     195,   1 Jan  6 03:03 nvidia1                  
crw-rw-rw-    1 root     root     195, 255 Jan  6 03:03 nvidiactl                
crw-rw----    1 root     lp         6,   0 Mar 15  2002 par0                     
crw-rw----    1 root     lp         6,   1 Mar 15  2002 par1                     
crw-rw----    1 root     lp         6,   2 Mar 15  2002 par2                     
-rw-r--r--    1 root     root       665509 Oct  7 16:41 pcm                      
crw-r-----    1 root     kmem       1,   4 Sep 28 18:06 port                     
crw-rw----    1 root     dip      108,   0 Sep 28 18:07 ppp                      
crw-------    1 root     root      10,   1 Mar 15  2002 psaux                    
crw-rw-rw-    1 root     root       1,   8 Sep 28 18:06 random                   
crw-rw----    1 root     root      10, 135 Mar 15  2002 rtc                      
brw-rw----    1 root     cdrom     11,   0 Mar 15  2002 scd0                     
brw-rw----    1 root     cdrom     11,   1 Mar 15  2002 scd1                     
brw-rw----    1 root     disk       8,   0 Mar 15  2002 sda                      
brw-rw----    1 root     disk       8,   1 Mar 15  2002 sda1                     
brw-rw----    1 root     disk       8,   2 Mar 15  2002 sda2                     
brw-rw----    1 root     disk       8,   3 Mar 15  2002 sda3                     
brw-rw----    1 root     disk       8,   4 Mar 15  2002 sda4                     
brw-rw----    1 root     disk       8,  16 Mar 15  2002 sdb                      
brw-rw----    1 root     disk       8,  17 Mar 15  2002 sdb1                     
brw-rw----    1 root     disk       8,  18 Mar 15  2002 sdb2                     
brw-rw----    1 root     disk       8,  19 Mar 15  2002 sdb3                     
brw-rw----    1 root     disk       8,  20 Mar 15  2002 sdb4                     
crw-rw----    1 root     audio     14,   1 Oct  7 16:26 sequencer                
lrwxrwxrwx    1 root     root           10 Oct  7 16:26 sequencer2 -> /dev/music 
lrwxrwxrwx    1 root     root            4 Sep 28 18:05 stderr -> fd/2           
lrwxrwxrwx    1 root     root            4 Sep 28 18:05 stdin -> fd/0            
lrwxrwxrwx    1 root     root            4 Sep 28 18:05 stdout -> fd/1           
crw-rw-rw-    1 root     tty        5,   0 Sep 28 18:06 tty                      
crw-------    1 root     root       4,   0 Sep 28 18:06 tty0                     
crw-------    1 root     root       4,   1 Jan 19 14:59 tty1                     
crw-rw----    1 root     dialout   62,  64 Oct  7 06:50 ttyLT0                   
crw-rw----    1 root     dialout    4,  64 Mar 15  2002 ttyS0                    
crw-rw----    1 root     dialout    4,  65 Mar 15  2002 ttyS1                    
crw-rw----    1 root     dialout    4,  66 Mar 15  2002 ttyS2                    
crw-rw----    1 root     dialout    4,  67 Mar 15  2002 ttyS3                    
crw-rw----    1 root     dialout  188,   0 Mar 15  2002 ttyUSB0                  
crw-rw----    1 root     dialout  188,   1 Mar 15  2002 ttyUSB1                  
cr--r--r--    1 root     root       1,   9 Jan 19 20:46 urandom                  
drwxr-xr-x    2 root     root         4096 Sep 28 18:05 usb                      
prw-r-----    1 root     adm             0 Jan 19 14:58 xconsole                 
crw-rw-rw-    1 root     root       1,   5 Sep 28 18:06 zero                     

Some common device files as well as their equivalent counterparts under
Windows that you may wish to remember are:

/dev/ttyS0 (First communications port, COM1)
     First serial port (mice, modems).
   
/dev/psaux (PS/2)
     PS/2 mouse connection (mice, keyboards).
   
/dev/lp0 (First printer port, LPT1)
     First parallel port (printers, scanners, etc).
   
/dev/dsp (First audio device)
     The name DSP comes from the term digital signal processor, a specialized
    processor chip optimized for digital signal analysis. Sound cards may use
    a dedicated DSP chip, or may implement the functions with a number of
    discrete devices. Other terms that may be used for this device are
    digitized voice and PCM.
   
/dev/usb (USB Devices)
     This subdirectory contains most of the USB device nodes. Device name
    allocations are fairly simplistic so no elaboration is be necessary.
   
/dev/sda (C:\, SCSI device)
     First SCSI device (HDD, Memory Sticks, external mass storage devices
    such as CD-ROM drives on laptops, etc).
   
/dev/scd (D:\, SCSI CD-ROM device)
     First SCSI CD-ROM device.
   
/dev/js0 (Standard gameport joystick)
     First joystick device.
   

Devices are defined by type, such as 'block' or 'character', and 'major' and
'minor' number. The major number is used to categorize a device and the minor
number is used to identify a specific device type. For example, all IDE
device connected to the primary controller have a major number of 3. Master
and slave devices, as well as individual partitions are further defined by
the use of minor numbers. These are the two numbers precede the date in the
following display:

# ls -l /dev/hd*

 
brw-rw----    1 root     disk       3,   0 Mar 15  2002 /dev/hda             
brw-rw----    1 root     disk       3,   1 Mar 15  2002 /dev/hda1            
brw-rw----    1 root     disk       3,  10 Mar 15  2002 /dev/hda10           
brw-rw----    1 root     disk       3,  11 Mar 15  2002 /dev/hda11           
brw-rw----    1 root     disk       3,  12 Mar 15  2002 /dev/hda12           
brw-rw----    1 root     disk       3,  13 Mar 15  2002 /dev/hda13           
brw-rw----    1 root     disk       3,  14 Mar 15  2002 /dev/hda14           
brw-rw----    1 root     disk       3,  15 Mar 15  2002 /dev/hda15           
brw-rw----    1 root     disk       3,  16 Mar 15  2002 /dev/hda16           
brw-rw----    1 root     disk       3,  17 Mar 15  2002 /dev/hda17           
brw-rw----    1 root     disk       3,  18 Mar 15  2002 /dev/hda18           
brw-rw----    1 root     disk       3,  19 Mar 15  2002 /dev/hda19           
brw-rw----    1 root     disk       3,   2 Mar 15  2002 /dev/hda2            
brw-rw----    1 root     disk       3,  20 Mar 15  2002 /dev/hda20           
brw-rw----    1 root     disk       3,   3 Mar 15  2002 /dev/hda3            
brw-rw----    1 root     disk       3,   4 Mar 15  2002 /dev/hda4            
brw-rw----    1 root     disk       3,   5 Mar 15  2002 /dev/hda5            
brw-rw----    1 root     disk       3,   6 Mar 15  2002 /dev/hda6            
brw-rw----    1 root     disk       3,   7 Mar 15  2002 /dev/hda7            
brw-rw----    1 root     disk       3,   8 Mar 15  2002 /dev/hda8            
brw-rw----    1 root     disk       3,   9 Mar 15  2002 /dev/hda9            
brw-rw----    1 root     disk       3,  64 Mar 15  2002 /dev/hdb             
brw-rw----    1 root     disk       3,  65 Mar 15  2002 /dev/hdb1            
brw-rw----    1 root     disk       3,  74 Mar 15  2002 /dev/hdb10           
brw-rw----    1 root     disk       3,  75 Mar 15  2002 /dev/hdb11           
brw-rw----    1 root     disk       3,  76 Mar 15  2002 /dev/hdb12           
brw-rw----    1 root     disk       3,  77 Mar 15  2002 /dev/hdb13           
brw-rw----    1 root     disk       3,  78 Mar 15  2002 /dev/hdb14           
brw-rw----    1 root     disk       3,  79 Mar 15  2002 /dev/hdb15           
brw-rw----    1 root     disk       3,  80 Mar 15  2002 /dev/hdb16           
brw-rw----    1 root     disk       3,  81 Mar 15  2002 /dev/hdb17           
brw-rw----    1 root     disk       3,  82 Mar 15  2002 /dev/hdb18           
brw-rw----    1 root     disk       3,  83 Mar 15  2002 /dev/hdb19           
brw-rw----    1 root     disk       3,  66 Mar 15  2002 /dev/hdb2            
brw-rw----    1 root     disk       3,  84 Mar 15  2002 /dev/hdb20           
brw-rw----    1 root     disk       3,  67 Mar 15  2002 /dev/hdb3            
brw-rw----    1 root     disk       3,  68 Mar 15  2002 /dev/hdb4            
brw-rw----    1 root     disk       3,  69 Mar 15  2002 /dev/hdb5            
brw-rw----    1 root     disk       3,  70 Mar 15  2002 /dev/hdb6            
brw-rw----    1 root     disk       3,  71 Mar 15  2002 /dev/hdb7            
brw-rw----    1 root     disk       3,  72 Mar 15  2002 /dev/hdb8            
brw-rw----    1 root     disk       3,  73 Mar 15  2002 /dev/hdb9            
brw-rw----    1 root     disk      22,   0 Mar 15  2002 /dev/hdc             
brw-rw----    1 root     disk      22,  64 Mar 15  2002 /dev/hdd             

The major number for both hda and hdb devices is 3. Of course, the minor
number changes for each specific partition. The definition of each major
number category can be examined by looking at the contents of the /usr/src/
linux/include/linux/major.h file. The devices.txt also documents major and
minor numbers. It is located in the /usr/src/linux/Documentation directory.
This file defines the major numbers. Almost all files devices are created by
default at the install time. However, you can always create a device using
the mknod command or the MAKEDEV script which is located in the /dev
directory itself. Devices can be created with this utility by supplying the
device to be created, the device type (block or character) and the major and
minor numbers. For example, let's say you have accidentally deleted /dev/
ttyS0 (COM1 under Windows), it can be recreated using the following command

# mknod ttyS0 c 4 64

For those of us who are rather lazy you can simply run the MAKEDEV script as
such

# MAKEDEV *

which will create all devices known.

If is possible that /dev may also contain a MAKEDEV.local for the creation of
any local device files.

In general and as required by the FSSTND, MAKEDEV will have provisions for
creating any device that may be found on the system, not just those that a
particular implementation installs.

For those of you who are wondering why Linux is using such a primitive system
to reference devices its because we haven't been able to devise a
sufficiently sophisticated mechanism which provides enough advantages over
the current system in order to achieve widespread adoption.

To date (as of kernel version 2.4), the best attempt has been made by Richard
Gooch of the CSIRO. It's called devfsd and has been a part of the kernel for
a number of years now. It has been sanctioned by the kernel developers and
Linus himself and details of its implementation can be found at /usr/src/
linux/Documentation/filesystems/devfs/README. Below is an excerpt from this
document.

Devfs is an alternative to "real" character and block special devices on your
root filesystem. Kernel device drivers can register devices by name rather
than major and minor numbers. These devices will appear in devfs
automatically, with whatever default ownership and protection the driver
specified. A daemon (devfsd) can be used to override these defaults. Devfs
has been in the kernel since 2.3.46.

NOTE that devfs is entirely optional. If you prefer the old disc-based device
nodes, then simply leave CONFIG_DEVFS_FS=n (the default). In this case,
nothing will change. ALSO NOTE that if you do enable devfs, the defaults are
such that full compatibility is maintained with the old devices names.

There are two aspects to devfs: one is the underlying device namespace, which
is a namespace just like any mounted filesystem. The other aspect is the
filesystem code which provides a view of the device namespace. The reason I
make a distinction is because devfs can be mounted many times, with each
mount showing the same device namespace. Changes made are global to all
mounted devfs filesystems. Also, because the devfs namespace exists without
any devfs mounts, you can easily mount the root filesystem by referring to an
entry in the devfs namespace.

The cost of devfs is a small increase in kernel code size and memory usage.
About 7 pages of code (some of that in __init sections) and 72 bytes for each
entry in the namespace. A modest system has only a couple of hundred device
entries, so this costs a few more pages. Compare this with the suggestion to
put /dev on a ramdisc.

On a typical machine, the cost is under 0.2 percent. On a modest system with
64 MBytes of RAM, the cost is under 0.1 percent. The accusations of
"bloatware" levelled at devfs are not justified.

As of kernel version 2.6, devfs has been marked obsolete and has now been
replaced by udev. A system very similar (at least from a the end user's point
of view) to devfs but which works entirely in userspace. An overview of udev
can be found at [http://www.kroah.com/linux/talks/ols_2003_udev_paper/
Reprint-Kroah-Hartman-OLS2003.pdf] http://www.kroah.com/linux/talks/
ols_2003_udev_paper/Reprint-Kroah-Hartman-OLS2003.pdf
-----------------------------------------------------------------------------

1.6. /etc

This is the nerve center of your system, it contains all system related
configuration files in here or in its sub-directories. A "configuration file"
is defined as a local file used to control the operation of a program; it
must be static and cannot be an executable binary. For this reason, it's a
good idea to backup this directory regularly. It will definitely save you a
lot of re-configuration later if you re-install or lose your current
installation. Normally, no binaries should be or are located here.

/etc/X11/
    This directory tree contains all the configuration files for the X Window
    System. Users should note that many of the files located in this
    directory are actually symbolic links to the /usr/X11R6 directory tree.
    Thus, the presence of these files in these locations can not be certain.
   
/etc/X11/XF86Config, /etc/X11/XF86Config-4
    The 'X' configuration file. Most modern distributions possess hardware
    autodetection systems that enable automatic creation of a valid file.
    Should autodetection fail a configuration file can also be created
    manually provided that you have sufficient knowledge about your system.
    It would be considered prudent not to attempt to type out a file from
    beginning to end. Rather, use common configuration utilities such as
    xf86config, XF86Setup and xf86cfg to create a workable template. Then,
    using suitable documentation commence optimization through intuition and/
    or trial and error. Options that can be configured via this file include
    X modules to be loaded on startup, keyboard, mouse, monitor and graphic
    chipset type. Often, commercial distributions will include their own X
    configuration utilities such as XDrake on Mandrake and also
    Xconfiguration on Redhat. Below is a sample X configuration file from the
    reference system
   
    ### BEGIN DEBCONF SECTION                                                    
    # XF86Config-4 (XFree86 server configuration file) generated by dexconf, the 
    # Debian X Configuration tool, using values from the debconf database.       
    #                                                                            
    # Edit this file with caution, and see the XF86Config-4 manual page.         
    # (Type "man XF86Config-4" at the shell prompt.)                             
    #                                                                            
    # If you want your changes to this file preserved by dexconf, only           
    # make changes                                                               
    # before the "### BEGIN DEBCONF SECTION" line above, and/or after the        
    # "### END DEBCONF SECTION" line below.                                      
    #                                                                            
    # To change things within the debconf section, run the command:              
    #   dpkg-reconfigure xserver-xfree86                                         
    # as root.  Also see "How do I add custom sections to a dexconf-             
    # generated                                                                  
    # XF86Config or XF86Config-4 file?" in /usr/share/doc/xfree86-               
    # common/FAQ.gz.                                                             
                                                                                 
    Section "Files"                                                              
            FontPath        "unix/:7100"                                         
    # local font server                                                          
            # if the local font server has problems,                             
    # we can fall back on these                                                  
            FontPath        "/usr/lib/X11/fonts/misc"                            
            FontPath        "/usr/lib/X11/fonts/cyrillic"                        
            FontPath        "/usr/lib/X11/fonts/100dpi/:unscaled"                
            FontPath        "/usr/lib/X11/fonts/75dpi/:unscaled"                 
            FontPath        "/usr/lib/X11/fonts/Type1"                           
            FontPath        "/usr/lib/X11/fonts/Speedo"                          
            FontPath        "/usr/lib/X11/fonts/100dpi"                          
            FontPath        "/usr/lib/X11/fonts/75dpi"                           
    EndSection                                                                   
                                                                                 
    Section "Module"                                                             
            Load        "GLcore"                                                 
            Load        "bitmap"                                                 
            Load        "dbe"                                                    
            Load        "ddc"                                                    
            Load        "dri"                                                    
            Load        "extmod"                                                 
            Load        "freetype"                                               
            Load        "glx"                                                    
            Load        "int10"                                                  
            Load        "pex5"                                                   
            Load        "record"                                                 
            Load        "speedo"                                                 
            Load        "type1"                                                  
            Load        "vbe"                                                    
            Load        "xie"                                                    
    EndSection                                                                   
                                                                                 
    Section "InputDevice"                                                        
            Identifier        "Generic Keyboard"                                 
            Driver                "keyboard"                                     
            Option                "CoreKeyboard"                                 
            Option                "XkbRules"        "xfree86"                    
            Option                "XkbModel"        "pc104"                      
            Option                "XkbLayout"        "us"                        
    EndSection                                                                   
                                                                                 
    Section "InputDevice"                                                        
            Identifier        "Configured Mouse"                                 
            Driver                "mouse"                                        
            Option                "CorePointer"                                  
            Option                "Device"                "/dev/psaux"           
            Option                "Protocol"                "NetMousePS/2"       
            Option                "Emulate3Buttons"        "true"                
            Option                "ZAxisMapping"                "4 5"            
    EndSection                                                                   
                                                                                 
    Section "InputDevice"                                                        
            Identifier        "Generic Mouse"                                    
            Driver                "mouse"                                        
            Option                "SendCoreEvents"        "true"                 
            Option                "Device"                "/dev/input/mice"      
            Option                "Protocol"                "ImPS/2"             
            Option                "Emulate3Buttons"        "true"                
            Option                "ZAxisMapping"                "4 5"            
    EndSection                                                                   
                                                                                 
    Section "Device"                                                             
            Identifier        "Generic Video Card"                               
            Driver                "nv"                                           
    #        Option                "UseFBDev"                "true"              
            Option                "UseFBDev"                "false"              
    EndSection                                                                   
                                                                                 
    Section "Monitor"                                                            
            Identifier        "Generic Monitor"                                  
            HorizSync        30-38                                               
            VertRefresh        43-95                                             
            Option                "DPMS"                                         
    EndSection                                                                   
                                                                                 
    Section "Screen"                                                             
            Identifier        "Default Screen"                                   
            Device                "Generic Video Card"                           
            Monitor                "Generic Monitor"                             
            DefaultDepth        16                                               
            SubSection "Display"                                                 
                    Depth                1                                       
                    Modes                "800x600" "640x480"                     
            EndSubSection                                                        
            SubSection "Display"                                                 
                    Depth                4                                       
                    Modes                "800x600" "640x480"                     
            EndSubSection                                                        
            SubSection "Display"                                                 
                    Depth                8                                       
                    Modes                "800x600" "640x480"                     
            EndSubSection                                                        
            SubSection "Display"                                                 
                    Depth                15                                      
                    Modes                "800x600" "640x480"                     
            EndSubSection                                                        
            SubSection "Display"                                                 
                    Depth                16                                      
                    Modes                "800x600" "640x480"                     
            EndSubSection                                                        
            SubSection "Display"                                                 
                    Depth                24                                      
                    Modes                "800x600" "640x480"                     
            EndSubSection                                                        
    EndSection                                                                   
                                                                                 
    Section "ServerLayout"                                                       
            Identifier        "Default Layout"                                   
            Screen                "Default Screen"                               
            InputDevice        "Generic Keyboard"                                
            InputDevice        "Configured Mouse"                                
            InputDevice        "Generic Mouse"                                   
    EndSection                                                                   
                                                                                 
    Section "DRI"                                                                
            Mode        0666                                                     
    EndSection                                                                   
                                                                                 
    ### END DEBCONF SECTION                                                      
   
    As you can see, the layout of the file is quite simple and tends to be
    quite standard across most distributions. At the top are the locations of
    the various font files for X (note - X will not start if you do not
    specify a valid font), next is the "Modules" section. It details what
    modules are to be loaded upon startup. The most well known extensions are
    probably GLX (required for 3D rendering of graphics and games) and
    Xinerama which allows users to expand their desktop over several
    monitors. Next are the various "Device" sections which describe the type
    of hardware you have. Improper configuration of these subsections can
    lead to heartache and trauma with seemingly misplaced keys, bewitched
    mice and also constant flashing as X attempts to restart in a sometimes
    never ending loop. In most cases when all else fails the vesa driver
    seems to be able to initialise most modern video cards. In the "Screen"
    section it is possible to alter the default startup resolution and depth.
    Quite often it is possible to alter these attributes on the fly by using
    the alt-ctrl-+ or alt-ctrl- set of keystrokes. Lastly are the
    "ServerLayout" and "DRI" sections. Users will almost never touch the
    "DRI" section and only those who wish to utilise the Xinerama extensions
    of X will require having to change any of the ServerLayout options.
   
/etc/X11/Xmodmap
    In general your default keyboard mapping comes from your X server setup.
    If this setup is insufficient and you are unwilling to go through the
    process of reconfiguration and/or you are not the superuser you'll need
    to use the xmodmap program. This is the utility's global configuration
    file.
   
/etc/X11/xkb/
    The various symbols, types, geometries of keymaps that the X server
    supports can be found in this directory tree.
   
/etc/X11/lbxproxy/
    Low Bandwidth X (LBX) proxy server configuration files. Applications that
    would like to take advantage of the Low Bandwidth extension to X (LBX)
    must make their connections to an lbxproxy. These applications need know
    nothing about LBX, they simply connect to the lbxproxy as if it were a
    regular X server. The lbxproxy accepts client connections, multiplexes
    them over a single connection to the X server, and performs various
    optimizations on the X protocol to make it faster over low bandwidth and/
    or high latency connections. It should be noted that such compression
    will not increase the pace of rendering all that much. Its primary
    purpose is to reduce network load and thus increase overall network
    latency. A competing project called DXPC (Differential X Protocol
    Compression) has been found to be more efficient at this task. Studies
    have shown though that in almost all cases ssh tunneling of X will
    produce far better results than through any of these specialised pieces
    of software.
   
/etc/X11/proxymngr/
    X proxy services manager initialisation files. proxymngr is responsible
    for resolving requests from xfindproxy (in the xbase-clients package) and
    other similar clients, starting new proxies when appropriate, and keeping
    track of all the available proxy services.
   
/etc/X11/xdm/
    X display manager configuration files. xdm manages a collection of X
    servers, which may be on the local host or remote machines. It provides
    services similar to those provided by init, getty, and login on
    character-based terminals: prompting for login name and password,
    authenticating the user, and running a session. xdm supports XDMCP (X
    Display Manager Control Protocol) and can also be used to run a chooser
    process which presents the user with a menu of possible hosts that offer
    XDMCP display management. If the xutils package is installed, xdm can use
    the sessreg utility to register login sessions to the system utmp file;
    this, however, is not necessary for xdm to function.
   
/etc/X11/xdm/xdm-config
    This is the master 'xdm' configuration file. It determines where all
    other 'xdm' configuration files will be located. It is almost certain to
    be left undisturbed.
   
/etc/X11/gdm/
    GNOME Display Manager configuration files. gdm provides the equivalent of
    a "login:" prompt for X displays- it pops up a login window and starts an
    X session. It provides all the functionality of xdm, including XDMCP
    support for managing remote displays. The greeting window is written
    using the GNOME libraries and hence looks like a GNOME application- even
    to the extent of supporting themes! By default, the greeter is run as an
    unprivileged user for security.
   
/etc/X11/gdm/gdm.conf
    This is the primary configuration file for GDM. Through it, users can
    specify whether they would like their system to automatically login as a
    certain user, background startup image and also if they would like to run
    their machine as somewhat of a terminal server by using the XDMCP
    protocol.
   
/etc/X11/fonts
    Home of xfs fonts.
   
/etc/X11/fs/
    X font server configuration files. xfs is a daemon that listens on a
    network port and serves X fonts to X servers (and thus to X clients). All
    X servers have the ability to serve locally installed fonts for
    themselves, but xfs makes it possible to offload that job from the X
    server, and/or have a central repository of fonts on a networked machine
    running xfs so that all the machines running X servers on a network do
    not require their own set of fonts. xfs may also be invoked by users to,
    for instance, make available X fonts in user accounts that are not
    available to the X server or to an already running system xfs.
   
/etc/X11/fs/config
    This is the 'xfs' initialisation file. It specifies the number of clients
    that are allowed to connect to the 'xfs' server at any one time, the
    location of log files, default resolution, the location of the fonts,
    etc.
   
                                                                                
    # font server configuration file                                            
    # $Xorg: config.cpp,v 1.3 2000/08/17 19:54:19 cpqbld Exp $                  
                                                                                
    # allow a maximum of 10 clients to connect to this font server              
    client-limit = 10                                                           
    # when a font server reaches its limit, start up a new one                  
    clone-self = on                                                             
    # log messages to /var/log/xfs.log (if syslog is not used)                  
    error-file = /var/log/xfs.log                                               
    # log errors using syslog                                                   
    use-syslog = on                                                             
    # turn off TCP port listening (Unix domain connections are still permitted) 
    no-listen = tcp                                                             
    # paths to search for fonts                                                 
    catalogue = /usr/lib/X11/fonts/misc/,/usr/lib/X11/fonts/cyrillic/,          
    /usr/lib/X11/fonts/100dpi/:unscaled,/usr/lib/X11/fonts/75dpi/:unscaled,     
    /usr/lib/X11/fonts/Type1/,/usr/lib/X11/fonts/CID,                           
    /usr/lib/X11/fonts/Speedo/,/usr/lib/X11/fonts/100dpi/,                      
    /usr/lib/X11/fonts/75dpi/                                                   
    # in decipoints                                                             
    default-point-size = 120                                                    
    # x1,y1,x2,y2,...                                                           
    default-resolutions = 100,100,75,75                                         
                                                                                
    # font cache control, specified in kB                                       
    cache-hi-mark = 2048                                                        
    cache-low-mark = 1433                                                       
    cache-balance = 70                                                          
   
/etc/X11/twm
    Home of configuration files for twm. The original Tabbed Window Manager.
   
/etc/X11/xinit/
    xinit configuration files. 'xinit' is a configuration method of starting
    up an X session that is designed to used as part of a script. Normally,
    this is used at larger sites as part of a tailored login process.
   
/etc/X11/xinit/xinitrc
    Global xinitrc file, used by all X sessions started by xinit (startx).
    Its usage is of course overridden by a .xinitrc file located in the home
    directory of a user.
   
/etc/adduser.conf
    'adduser' configuration. The adduser command can create new users, groups
    and add existing users to existing groups. Adding users with adduser is
    much easier than adding them by hand. Adduser will choose appropriate UID
    and GID values, create a home directory, copy skeletal user configuration
    from /etc/skel, allow you to set an initial password and the GECOS field.
    Optionally a custom script can be executed after this commands. See
    adduser(8) and adduser.conf(5) for full documentation.
   
/etc/adjtime
    Has parameters to help adjust the software (kernel) time so that it
    matches the RTC.
   
/etc/aliases
    This is the aliases file - it says who gets mail for whom. It was
    originally generated by `eximconfig', part of the exim package
    distributed with Debian, but it may edited by the mail system
    administrator. See exim info section for details of the things that can
    be configured here. An aliases database file (aliases.db) is built from
    the entries in the aliases files by the newaliases utility.
   
/etc/alternatives
    It is possible for several programs fulfilling the same or similar
    functions to be installed on a single system at the same time. For
    example, many systems have several text editors installed at once. This
    gives choice to the users of a system, allowing each to use a different
    editor, if desired, but makes it difficult for a program to make a good
    choice of editor to invoke if the user has not specified a particular
    preference.
   
    The alternatives system aims to solve this problem. A generic name in the
    filesystem is shared by all files providing interchangeable
    functionality. The alternatives system and the system administrator
    together determine which actual file is referenced by this generic name.
    For example, if the text editors ed(1) and nvi(1) are both installed on
    the system, the alternatives system will cause the generic name /usr/bin/
    editor to refer to /usr/bin/nvi by default. The system administrator can
    override this and cause it to refer to /usr/bin/ed instead, and the
    alternatives system will not alter this setting until explicitly
    requested to do so.
   
    The generic name is not a direct symbolic link to the selected
    alternative. Instead, it is a symbolic link to a name in the alternatives
    directory, which in turn is a symbolic link to the actual file
    referenced. This is done so that the system administrator's changes can
    be confined within the /etc directory.
   
/etc/apt
     This is Debian's next generation front-end for the dpkg package manager.
    It provides the apt-get utility and APT dselect method that provides a
    simpler, safer way to install and upgrade packages. APT features complete
    installation ordering, multiple source capability and several other
    unique features, see the Users Guide in /usr/share/doc/apt/guide.text.gz
   
/etc/apt/sources.list
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-7 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-6 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-5 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-4 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-3 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-2 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
    deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-1 (20020718)]/  
              unstable contrib main non-US/contrib non-US/main                        
                                                                                      
    # deb http://security.debian.org/ stable/updates main                             
   
      Contains a list of apt-sources from which packages may be installed via
    APT.
   
/etc/asound.conf
    ALSA (Advanced Linux Sound Architecture) configuration file. It is
    normally created via alsactl or other third-party sound configuration
    utilities that may be specific to a distribution such as sndconfig from
    Redhat.
   
/etc/at.deny
    Users denied access to the at daemon. The 'at' command allows user to
    execute programs at an arbitrary time.
   
/etc/autoconf
    Configuration files for autoconf. 'autoconf' creates scripts to configure
    source code packages using templates. To create configure from
    configure.in, run the autoconf program with no arguments. autoconf
    processes configure.ac with the m4 macro processor, using the Autoconf
    macros. If you give autoconf an argument, it reads that file instead of
    configure.ac and writes the configuration script to the standard output
    instead of to configure. If you give autoconf the argument -, it reads
    the standard input instead of configure.ac and writes the configuration
    script on the standard output.
   
    The Autoconf macros are defined in several files. Some of the files are
    distributed with Autoconf; autoconf reads them first. Then it looks for
    the optional file acsite.m4 in the directory that contains the
    distributed Autoconf macro files, and for the optional file aclocal.m4 in
    the current directory. Those files can contain your site's or the
    package's own Autoconf macro definitions. If a macro is defined in more
    than one of the files that autoconf reads, the last definition it reads
    overrides the earlier ones.
   
/etc/bash.bashrc
    System wide functions and aliases' file for interactive bash shells.
   
/etc/bash_completion
    Programmable completion functions for bash 2.05a.
   
/etc/chatscripts/provider
    This is the chat script used to dial out to your default service
    provider.
   
/etc/cron.d, /etc/cron.daily, /etc/cron.weekly, /etc/cron.monthly
    These directories contain scripts to be executed on a regular basis by
    the cron daemon.
   
/etc/crontab
    'cron' configuration file. This file is for the cron table to setup the
    automatic running of system routines. A cron table can also be
    established for individual users. The location of these user cron table
    files will be explained later on.
   
    # /etc/crontab: system-wide crontab                                               
    # Unlike any other crontab you don't have to run the `crontab'                    
    # command to install the new version when you edit this file.                     
    # This file also has a username field, that none of the other crontabs do.        
                                                                                      
    SHELL=/bin/sh                                                                     
    PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin                 
                                                                                      
    # m h dom mon dow user command                                                    
    25 6 * * * root test -e /usr/sbin/anacron || run-parts --report /etc/cron.daily   
    47 6 * * 7 root test -e /usr/sbin/anacron || run-parts --report /etc/cron.weekly  
    52 6 1 * * root test -e /usr/sbin/anacron || run-parts --report /etc/cron.monthly 
    #                                                                                 
   
/etc/csh.login
    System-wide .login file for csh(1). This file is sourced on all
    invocations of the shell. It contains commands that are to be executed
    upon login and sometimes aliases also.
   
/etc/csh.logout
    System-wide .logout file for csh(1). This file is sourced on all
    invocations of the shell. It contains commands that are to be executed
    upon logout.
   
/etc/csh.cshrc
    System-wide .cshrc file for csh(1). This file is sourced on all
    invocations of the shell. This file should contain commands to set the
    command search path, plus other important environment variables. This
    file should not contain commands that produce output or assume the shell
    is attached to a tty.
   
/etc/cups
    Configuration files for the Common UNIX Printing System (CUPS). Files
    here are used to define client-specific parameters, such as the default
    server or default encryption settings.
   
/etc/deluser.conf
    'deluser' configuration files. The deluser command can remove users and
    groups and remove users from a given group. Deluser can optionally remove
    and backup the user's home directory and mail spool or all files on the
    system owned by him. Optionally a custom script can also be executed
    after each of the commands.
   
/etc/devfs
      This daemon sets up the /dev filesystem for use. It creates required
    symbolic links in /dev and also creates (if so configured, as is the
    default) symbolic links to the "old" names for devices.
   
/etc/devfs/conf.d/
    'devfsd' configuration files. This daemon sets up the /dev filesystem for
    use. It creates required symbolic links in /dev and also creates (if so
    configured, as is the default) symbolic links to the "old" names for
    devices.
   
/etc/dhclient.conf, /etc/dhclient-script
    'dhclient' configuration file and 'dhclient' script files respectively.
    It configures your system so that it may act as a client on a DHCP based
    network. It is essential to connect to the Internet nowadays.
   
/etc/dict.conf
    #  /etc/dict.conf Written by Bob Hilliard <hilliard@debian.org>          
    #  1998/03/20.  Last revised Sun, 22 Nov 1998 18:10:04 -0500 This is     
    #  the configuration file for /usr/bin/dict.  In most cases only the     
    #  server keyword need be specified.                                     
                                                                             
    #  This default configuration will try to access a dictd server on       
    #  the local host, failing that, it will try the public server.  In      
    #  many cases this will be slow, so you should comment out the line      
    #  for the server that you don't want to use. To use any other           
    #  server, enter its IP address in place of "dict.org".                  
                                                                             
    #  Refer to the dict manpage (man dict) for other options that could     
    #  be inserted in here.                                                  
                                                                             
    server localhost                                                         
    server dict.org                                                          
   
     dict is a client for the Dictionary Server Protocol (DICT), a TCP
    transaction based query/response protocol that provides access to
    dictionary definitions from a set of natural language dictionary
    databases.
   
/etc/dosemu.conf
    Configuration file for the Linux DOS Emulator. DOSEMU is a PC Emulator
    application that allows Linux to run a DOS operating system in a virtual
    x86 machine. This allows you to run many DOS applications. It includes
    the FreeDOS kernel, color text and full keyboard emulation (via hotkeys)
    via terminal, built-in X support, IBM character set font, graphics
    capability at the console with most compatible video cards, DPMI support
    so you can run DOOM, CDROM support, builtin IPX and pktdrvr support. Note
    - 'dosemu' is simply a ported version of Corel's own PC-DOS.
   
/etc/email-addresses
    Part of the exim package. This file contains email addresses to use for
    outgoing mail. Any local part not in here will be qualified by the system
    domain as normal. It should contain lines of the form:
   
   
          user: someone@isp.com                                              
          otheruser: someoneelse@anotherisp.com                              
                                                                             
       
   
    Exim is an MTA that is considered to be rather easier to configure than
    smail or sendmail. It is a drop-in replacement for sendmail, mailq and
    rsmtp. Advanced features include the ability to reject connections from
    known spam sites, and an extremely efficient queue processing algorithm.
/etc/esound.conf
    ESD configuration files. The Enlightened sound daemon is designed to mix
    together several digitized audio streams for playback by a single device.
    Like nasd, artsd and rplay it also has the capability to play sounds
    remotely.
   
/etc/exports
    The control list of systems who want to access the system via NFS, a the
    list of directories that you would like to share and the permissions
    allocated on each share.
   
      # /etc/exports: the access control list for filesystems which may be         
      # exported to NFS clients.  See exports(5).                                  
      ## LTS-begin ##                                                              
                                                                                   
      #                                                                            
      # The lines between the 'LTS-begin' and the 'LTS-end' were added             
      # on: Sun Feb 23 05:54:17 EST 2003 by the ltsp installation script.          
      # For more information, visit the ltsp homepage                              
      # at http://www.ltsp.org                                                     
      #                                                                            
                                                                                   
      /opt/ltsp/i386                  192.168.0.0/255.255.255.0(ro,no_root_squash) 
      /var/opt/ltsp/swapfiles         192.168.0.0/255.255.255.0(rw,no_root_squash) 
                                                                                   
      #                                                                            
      # The following entries need to be uncommented if you want                   
      # Local App support in ltsp                                                  
      #                                                                            
      #/home                  192.168.0.0/255.255.255.0(rw,no_root_squash)         
                                                                                   
      ## LTS-end ##                                                                
   
/etc/fdprm
    Floppy disk parameter table. Describes what different floppy disk formats
    look like. Used by setfdprm.
   
/etc/fstab
    The configuration file for 'mount' and now 'supermount'. It lists the
    filesystems mounted automatically at startup by the mount -a command (in
    /etc/rc or equivalent startup file). Under Linux, also contains
    information about swap areas used automatically by swapon -a.
   
   
         
          # /etc/fstab: static file system information.                              
          #                                                                          
          # The following is an example. Please see fstab(5) for further details.    
          # Please refer to mount(1) for a complete description of mount options.    
          #                                                                          
          # Format:                                                                  
          # <file system> <mount point> <type> <options> <dump> <pass>               
          #                                                                          
          # dump(8) uses the <dump> field to determine which file systems need       
          # to be dumped. fsck(8) uses the <pass> column to determine which file     
          # systems need to be checked--the root file system should have a 1 in      
          # this field, other file systems a 2, and any file systems that should     
          # not be checked (such as MS-DOS or NFS file systems) a 0.                 
          #                                                                          
          # The `sw' option indicates that the swap partition is to be activated     
          # with `swapon -a'.                                                        
          /dev/hda2 none swap sw 0 0                                                 
          # The `bsdgroups' option indicates that the file system is to be mounted   
          # with BSD semantics (files inherit the group ownership of the directory   
          # in which they live). `ro' can be used to mount a file system read-only.  
          /dev/hda3 / ext2 defaults 0 1                                              
          /dev/hda5 /home ext2 defaults 0 2                                          
          /dev/hda6 /var ext2 defaults 0 2                                           
          /dev/hda7 /usr ext2 defaults,ro 0 2                                        
          /dev/hda8 /usr/local ext2 defaults,bsdgroups 0 2                           
          # The `noauto' option indicates that the file system should not be mounted 
          # with `mount -a'. `user' indicates that normal users are allowed to mount 
          # the file system.                                                         
          /dev/cdrom /cdrom iso9660 defaults,noauto,ro,user 0 0                      
          /dev/fd0 /floppy minix defaults,noauto,user 0 0                            
          /dev/fd1 /floppy minix defaults,noauto,user 0 0                            
          # NFS file systems: server:                                                
          /export/usr /usr nfs defaults 0 0                                          
          # proc file system:                                                        
          proc /proc proc defaults 0 0                                               
                                                                                     
       
   
   
/etc/ftpaccess
    Determines who might get ftp-access to your machine.
   
/etc/ftpchroot
    List of ftp users that need to be chrooted.
   
/etc/ftpuser
    List of disallowed ftp users.
   
/etc/gateways
    Lists gateways for 'routed'.
   
/etc/gettydefs
    Configures console-logins.
   
/etc/gnome-vfs-mime-magic
    MIME magic patterns as used by the Gnome VFS library.
   
/etc/group
    Similar to /etc/passwd. It lists the configured user groups and who
    belongs to them.
   
/etc/group-
    Old /etc/group file.
   
/etc/gshadow
    Contains encrypted forms of group passwords.
   
/etc/gshadow-
    Old /etc/gshadow file.
   
/etc/hostname
    Contains the hostname of your machine (can be fully qualified or not).
   
/etc/host.conf
    Determines the search order for look-ups (usually hosts bind, i.e. "check
    /etc/hosts first and then look for a DNS").
   
/etc/hosts
    This file is used to define a system name and domain combination with a
    specific IP address. This file needs to always contain an entry for an IP
    address, if the machine is connected to the network.
   
      ### etherconf DEBCONF AREA. DO NOT EDIT THIS AREA OR INSERT TEXT BEFORE IT.  
      127.0.0.1 localhost ::1 localhost                                            
      ip6-localhost ip6-loopback                                                   
      fe00::0 ip6-localnet                                                         
      ff00::0 ip6-mcastprefix                                                      
      ff02::1 ip6-allnodes                                                         
      ff02::2 ip6-allrouters                                                       
      ff02::3 ip6-allhosts                                                         
      192.168.0.99 debian.localdomain.com debian                                   
      ### END OF DEBCONF AREA. PLACE YOUR EDITS BELOW; THEY WILL BE PRESERVED.     
      192.168.0.1 ws001                                                            
                                                                                   
   
/etc/hosts.allow
    Part of the tcp-wrappers system to control access to your machine's
    services. It lists hosts that are allowed to access the system and
    specific daemons.
   
      # /etc/hosts.allow: list of hosts that are allowed to access the       
      # system.                                                              
      # See the manual pages hosts_access(5), hosts_options(5)               
      # and /usr/doc/netbase/portmapper.txt.gz                               
      #                                                                      
      # Example: ALL: LOCAL @some_netgroup                                   
      # ALL: .foobar.edu EXCEPT terminalserver.foobar.edu                    
      #                                                                      
      # If you're going to protect the portmapper use the name "portmap"     
      # for the daemon name. Remember that you can only use the keyword      
      # "ALL" and IP addresses (NOT host or domain names) for the            
      # portmapper. See portmap(8) and /usr/doc/portmap/portmapper.txt.gz    
      # for further information.                                             
      bootpd: 0.0.0.0 in.tftpd: 192.168.0.                                   
      portmap: 192.168.0.                                                    
      rpc.mountd: 192.168.0.                                                 
      rpc.nfsd: 192.168.0.                                                   
      gdm: 192.168.0.                                                        
      nasd: 192.168.0.                                                       
                                                                             
   
/etc/hosts.deny
    part of the tcp-wrappers system to control access to your machine's
    services. It lists hosts that are not allowed to access the system.
   
      # Example: ALL: some.host.name, .some.domain                           
      # ALL EXCEPT in.fingerd: other.host.name, .other.domain                
      #                                                                      
      # If you're going to protect the portmapper use the name "portmap"     
      # for the daemon name. Remember that you can only use the keyword      
      # "ALL" and IP addresses (NOT host or domain names) for the            
      # portmapper. See portmap(8) and /usr/doc/portmap/portmapper.txt.gz    
      # for further information.                                             
      #                                                                      
      # The PARANOID wildcard matches any host whose name does not match     
      # its address. You may wish to enable this to ensure any programs      
      # that don't validate looked up hostnames still leave understandable   
      # logs. In past versions of Debian this has been the default.          
      # ALL: PARANOID                                                        
                                                                             
   
/etc/httpd
    Apache configuration files. Apache is a versatile, high-performance HTTP
    server. The most popular server in the world, Apache features a modular
    design and supports dynamic selection of extension modules at runtime.
    Its strong points are its range of possible customization, dynamic
    adjustment of the number of server processes, and a whole range of
    available modules including many authentication mechanisms, server-parsed
    HTML, server-side includes, access control, CERN httpd metafiles
    emulation, proxy caching, etc. Apache also supports multiple virtual
    homing.
   
/etc/identd.conf
    TCP/IP IDENT protocol server. It implements the TCP/IP proposed standard
    IDENT user identification protocol (RFC 1413). identd operates by looking
    up specific TCP/IP connections and returning the username of the process
    owning the connection. It can also return other information besides the
    username.
   
      # /etc/identd.conf - an example configuration file                         
                                                                                 
                                                                                 
      #-- The syslog facility for error messages                                 
      # syslog:facility = daemon                                                 
                                                                                 
                                                                                 
      #-- User and group (from passwd database) to run as                        
      server:user = nobody                                                       
                                                                                 
      #-- Override the group id                                                  
      # server:group = kmem                                                      
                                                                                 
      #-- What port to listen on when started as a daemon or from /etc/inittab   
      # server:port = 113                                                        
                                                                                 
      #-- The socket backlog limit                                               
      # server:backlog = 256                                                     
                                                                                 
      #-- Where to write the file containing our process id                      
      # server:pid-file = "/var/run/identd/identd.pid"                           
                                                                                 
      #-- Maximum number of concurrent requests allowed (0 = unlimited)          
      # server:max-requests = 0                                                  
                                                                                 
      #-- Enable some protocol extensions like "VERSION" or "QUIT"               
      protocol:extensions = enabled                                              
                                                                                 
      #-- Allow multiple queries per connection                                  
      protocol:multiquery = enabled                                              
                                                                                 
      #-- Timeout in seconds since connection or last query. Zero = disable      
      # protocol:timeout = 120                                                   
                                                                                 
      #-- Maximum number of threads doing kernel lookups                         
      # kernel:threads = 8                                                       
                                                                                 
      #-- Maximum number of queued kernel lookup requests                        
      # kernel:buffers = 32                                                      
                                                                                 
      #-- Maximum number of time to retry a kernel lookup in case of failure     
      # kernel:attempts = 5                                                      
                                                                                 
                                                                                 
                                                                                 
      #-- Disable username lookups (only return uid numbers)                     
      # result:uid-only = no                                                     
                                                                                 
      #-- Enable the ".noident" file                                             
      # result:noident = enabled                                                 
                                                                                 
      #-- Charset token to return in replies                                     
      # result:charset = "US-ASCII"                                              
                                                                                 
      #-- Opsys token to return in replies                                       
      # result:opsys = "UNIX"                                                    
                                                                                 
      #-- Log all request replies to syslog (none == don't)                      
      # result:syslog-level = none                                               
                                                                                 
                                                                                 
      #-- Enable encryption (only available if linked with a DES library)        
      # result:encrypt = no                                                      
                                                                                 
      #-- Path to the DES key file (only available if linked with a DES library) 
      # encrypt:key-file = "/usr/local/etc/identd.key"                           
                                                                                 
                                                                                 
      #-- Include a machine local configuration file                             
      # include = /etc/identd.conf                                               
                                                                                 
   
/etc/inetd.conf
    Configuration of services that are started by the INETD TCP/IP super
    server. 'inetd' is now deprecated. 'xinetd' has taken its place. See /etc
    /xinet.conf for further details.
   
      # /etc/inetd.conf:  see inetd(8) for further information.              
      #                                                                      
      # Internet server configuration database                               
      #                                                                      
      #                                                                      
      # Lines starting with "#:LABEL:" or "#<off>#" should not               
      # be changed unless you know what you are doing!                       
      #                                                                      
      # If you want to disable an entry so it isn't touched during           
      # package updates just comment it out with a single '#' character.     
      #                                                                      
      # Packages should modify this file by using update-inetd(8)            
      #                                                                      
      # <service_name> <sock_type> <proto>                                   
      # <flags> <user> <server_path>                                         
      # <args>                                                               
      #                                                                      
      #:INTERNAL: Internal services                                          
      #echo stream  tcp nowait root internal                                 
      #echo dgram   udp wait root internal                                   
      #chargen stream tcp   nowait root internal                             
      #chargen dgram udp    wait root internal                               
      discard stream tcp nowait root internal                                
      discard dgram udp wait root internal                                   
      daytime stream tcp nowait root internal                                
      #daytime dgram udp wait root internal                                  
      time stream tcp nowait root internal                                   
      #time dgram udp wait root internal                                     
                                                                             
      #:STANDARD: These are standard services.                               
      ftp stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.ftpd            
      telnet stream tcp nowait telnetd.telnetd /usr/sbin/tcpd                
                                               /usr/sbin/in.telnetd          
                                                                             
      #:MAIL: Mail, news and uucp services.                                  
      smtp stream tcp nowait mail /usr/sbin/exim exim -bs                    
      imap2  stream  tcp nowait root /usr/sbin/tcpd /usr/sbin/imapd          
      imap3  stream  tcp nowait root /usr/sbin/tcpd /usr/sbin/imapd          
                                                                             
      #:INFO: Info services                                                  
      ident stream tcp wait identd /usr/sbin/identd identd                   
      finger stream tcp nowait nobody /usr/sbin/tcpd                         
                                      /usr/sbin/in.fingerd                   
                                                                             
      #:BOOT: Tftp service is provided primarily for booting.                
      #Most sites run this only on machines acting as "boot servers."        
      tftp dgram udp wait nobody /usr/sbin/tcpd                              
                                 /usr/sbin/in.tftpd -s /tftpboot             
                                                                             
   
/etc/init.d
    Order of scripts run in /etc/rc?.d                                            
    ==================================                                            
                                                                                  
    0. Overview.                                                                  
                                                                                  
       All scripts executed by the init system are located in /etc/init.d.        
       The directories /etc/rc?.d (? = S, 0 .. 6) contain relative links to       
       those scripts. These links are named S<2-digit-number><                    
       original-name> or K<2-digit-number><original-name>.                        
                                                                                  
       If a scripts has the ".sh" suffix it is a bourne shell script and          
       MAY be handled in an optimized manner. The behaviour of executing the      
       script in an optimized way will not differ in any way from it being        
       forked and executed in the regular way.                                    
                                                                                  
       The following runlevels are defined:                                       
                                                                                  
       N       System bootup (NONE).                                              
       S       Single user mode (not to be switched to directly)                  
       0       halt                                                               
       1       single user mode                                                   
       2 .. 5  multi user mode                                                    
       6       reboot                                                             
                                                                                  
    1. Boot.                                                                      
                                                                                  
       When the systems boots, the /etc/init.d/rcS script is executed. It         
       in turn executes all the S* scripts in /etc/rcS.d in alphabetical          
       (and thus numerical) order. The first argument passed to the               
       executed scripts is "start". The runlevel at this point is                 
       "N" (none).                                                                
                                                                                  
       Only things that need to be run once to get the system in a consistent     
       state are to be run. The rcS.d directory is NOT meant to replace rc.local. 
       One should not start daemons in this runlevel unless absolutely            
       necessary. Eg, NFS might need the portmapper, so it is OK to start it      
       early in the boot process. But this is not the time to start the           
       squid proxy server.                                                        
                                                                                  
    2. Going multiuser.                                                           
                                                                                  
       After the rcS.d scripts have been executed, init switches to the           
       default runlevel as specified in /etc/inittab, usually "2".                
                                                                                  
       Init then executes the /etc/init.d/rc script which takes care of           
       starting the services in /etc/rc2.d.                                       
                                                                                  
       Because the previous runlevel is "N" (none) the /etc/rc2.d/KXXxxxx         
       scripts will NOT be executed - there is nothing to stop yet,               
       the system is busy coming up.                                              
                                                                                  
       If for example there is a service that wants to run in runlevel 4          
       and ONLY in that level, it will place a KXXxxxx script in                  
       /etc/rc{2,3,5}.d to stop the service when switching out of runlevel 4.     
       We do not need to run that script at this point.                           
                                                                                  
       The /etc.rc2.d/SXXxxxx scripts will be executed in alphabetical            
       order, with the first argument set to "start".                             
                                                                                  
    3. Switching runlevels.                                                       
                                                                                  
       When one switches from (for example) runlevel 2 to runlevel 3,             
       /etc/init.d/rc will first execute in alphabetical order all K              
       scripts for runlevel 3 (/etc/rc3.d/KXXxxxx) with as first argument         
       "stop" and then all S scripts for runlevel 3 (/etc/rc3.d/SXXxxxx)          
       with as first argument "start".                                            
                                                                                  
       As an optimization, a check is made for each "service" to see if           
       it was already running in the previous runlevel. If it was, and there      
       is no K (stop) script present for it in the new runlevel, there is         
       no need to start it a second time so that will not be done.                
                                                                                  
       On the other hand, if there was a K script present, it is assumed the      
       service was stopped on purpose first and so needs to be restarted.         
                                                                                  
       We MIGHT make the same optimization for stop scripts as well-              
       if no S script was present in the previous runlevel, we can assume         
       that service was not running and we don't need to stop it either.          
       In that case we can remove the "coming from level N" special case          
       mentioned above in 2). But right now that has not been implemented.        
                                                                                  
    4. Single user mode.                                                          
                                                                                  
       Switching to single user mode is done by switching to runlevel 1.          
       That will cause all services to be stopped (assuming they all have         
       a K script in /etc/rc1.d). The runlevel 1 scripts will then switch         
       to runlevel "S" which has no scripts - all it does is spawn                
       a shell directly on /dev/console for maintenance.                          
                                                                                  
    5. Halt/reboot                                                                
                                                                                  
       Going to runlevel 0 or 6 will cause the system to be halted or rebooted,   
       respectively. For example, if we go to runlevel 6 (reboot) first           
       all /etc/rc6.d/KXXxxxx scripts will be executed alphabetically with        
       "stop" as the first argument.                                              
                                                                                  
       Then the /etc/rc6.d/SXXxxxx scripts will be executed alphabetically        
       with "stop" as the first argument as well. The reason is that there        
       is nothing to start any more at this point - all scripts that are          
       run are meant to bring the system down.                                    
                                                                                  
       In the future, the /etc/rc6.d/SXXxxxx scripts MIGHT be moved to            
       /etc/rc6.d/K1XXxxxx for clarity.                                           
   
/etc/inittab
    Boot-time system configuration/initialization script. Tells init how to
    handle runlevels. It sets the default runlevel. This is run first except
    when booting in emergency (-b) mode. It also enables a user to startup a
    getty session on an external device such as the serial ports. To add
    terminals or dial-in modem lines to a system, just add more lines to /etc
    /inittab, one for each terminal or dial-in line. For more details, see
    the manual pages init, inittab, and getty. If a command fails when it
    starts, and init is configured to restart it, it will use a lot of system
    resources: init starts it, it fails, init starts it, it fails, and so on.
    To prevent this, init will keep track of how often it restarts a command,
    and if the frequency grows to high, it will delay for five minutes before
    restarting again. /etc/inittab also has some special features that allow
    init to react to special circumstances. powerwait Allows init to shut the
    system down, when the power fails. This assumes the use of a UPS, and
    software that watches the UPS and informs init that the power is off.
    ctrlaltdel Allows init to reboot the system, when the user presses
    ctrl-alt-del on the console keyboard. Note that the system administrator
    can configure the reaction to ctrl-alt-del to be something else instead,
    e.g., to be ignored, if the system is in a public location. sysinit
    Command to be run when the system is booted. This command usually cleans
    up /tmp, for example. The list above is not exhaustive. See your inittab
    manual page for all possibilities, and for details on how to use the ones
    above. To set (or reset) initial terminal colours. The following shell
    script should work for VGA consoles: for n in 1 2 4 5 6 7 8; do setterm
    -fore yellow -bold on -back blue -store > /dev/tty$n done Substitute your
    favorite colors, and use /dev/ttyS$n for serial terminals. To make sure
    they are reset when people log out (if they've been changed) replace the
    references to getty (or mingetty or uugetty or whatever) in /etc/inittab
    with references to /sbin/mygetty. #!/bin/sh setterm -fore yellow -bold on
    -back blue -store > $1 exec /sbin/mingetty $@ An example /etc/inittab is
    provided below.
   
      # /etc/inittab: init(8) configuration.                                       
      # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $                         
      # The default runlevel. id:2:initdefault:                                    
      # Boot-time system configuration/initialization script.                      
      # This is run first except when booting in emergency (-b) mode.              
      si::sysinit:/etc/init.d/rcS                                                  
      # What to do in single-user mode.                                            
      ~~:S:wait:/sbin/sulogin                                                      
      # /etc/init.d executes the S and K scripts upon change                       
      # of runlevel.                                                               
      #                                                                            
      # Runlevel 0 is halt.                                                        
      # Runlevel 1 is single-user.                                                 
      # Runlevels 2-5 are multi-user.                                              
      # Runlevel 6 is reboot.                                                      
      l0:0:wait:/etc/init.d/rc 0 l1:1:wait:/etc/init.d/rc 1                        
      l2:2:wait:/etc/init.d/rc 2 l3:3:wait:/etc/init.d/rc 3                        
      l4:4:wait:/etc/init.d/rc 4 l5:5:wait:/etc/init.d/rc 5                        
      l6:6:wait:/etc/init.d/rc 6                                                   
      # Normally not reached, but fallthrough in case of emergency.                
      z6:6:respawn:/sbin/sulogin                                                   
      # What to do when CTRL-ALT-DEL is pressed.                                   
      ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now                             
      # Action on special keypress (ALT-UpArrow).                                  
      #kb::kbrequest:/bin/echo "Keyboard Request                                   
      #--edit /etc/inittab to let this work."                                      
      # What to do when the power fails/returns.                                   
      pf::powerwait:/etc/init.d/powerfail start                                    
      pn::powerfailnow:/etc/init.d/powerfail now                                   
      po::powerokwait:/etc/init.d/powerfail stop                                   
      # /sbin/getty invocations for the runlevels.                                 
      #                                                                            
      # The "id" field MUST be the same as the last                                
      # characters of the device (after "tty").                                    
      #                                                                            
      # Format:                                                                    
      # <id>:<runlevels>:<action>:<process>                                        
      #                                                                            
      # Note that on most Debian systems tty7 is used by the X Window System,      
      # so if you want to add more getty's go ahead but skip tty7 if you run X.    
      #                                                                            
      1:2345:respawn:/sbin/getty 38400 tty1 2:23:respawn:/sbin/getty 38400 tty2    
      3:23:respawn:/sbin/getty 38400 tty3 4:23:respawn:/sbin/getty 38400 tty4      
      5:23:respawn:/sbin/getty 38400 tty5 6:23:respawn:/sbin/getty 38400 tty6      
      # Example how to put a getty on a serial line (for a terminal)               
      #                                                                            
      #T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100                               
      #T1:23:respawn:/sbin/getty -L ttyS1 9600 vt100                               
      # Example how to put a getty on a modem line.                                
      #                                                                            
      #T3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3                               
                                                                                   
      Undocumented features                                                        
                                                                                   
      The letters A-C can be used to spawn a daemon listed in /etc/inittab. For    
      example, assuming you want to start getty on a port to receive a call, but   
      only after receiving a voice call first (and not all the time). Furthermore, 
      you want to be able to receive a data or a fax call and that when you get    
      the voice message you'll know which you want. You insert two new lines       
      in /etc/inittab, each with its own ID, and each with a runlevel such as A    
      for data and B for fax. When you know which you need, you simply spawn the   
      appropriate daemon by calling 'telinit A' or 'telinit B'.                    
      The appropriate getty is put on the line until the first call is received.   
      When the caller terminates the connection, the getty drops because, by       
      definition, on demand will not respawn. The other two letters, S and Q, are  
      special. S brings you system to maintenance mode and is the same as changing 
      state to runlevel 1. The Q is used to tell init to reread inittab. The       
      /etc/inittab file can be changed as often as required, but will only be read 
      under certain circumstances: -One of its processes dies (do you need to      
      respawn another?) -On a powerful signal from a power daemon (or a command    
      line) -When told to change state by telinit The Q argument tells init to     
      reread the /etc/inittab file. Even though it is called the System V runlevel 
      system runlevels 7-9 are legitimate runlevels that can be used if necessary. 
      The administrator must remember to alter the inittab file though and also to 
      create the required rc?.d files.                                             
   
/etc/inputrc
    Global inputrc for libreadline. Readline is a function that gets a line
    from a user and automatically edits it.
   
/etc/isapnp.conf
    Configuration file for ISA based cards. This standard is virtually
    redundant in new systems. The 'isapnptools' suite of ISA Plug-And-Play
    configuration utilities is used to configure such devices. These programs
    are suitable for all systems, whether or not they include a PnP BIOS. In
    fact, PnP BIOS adds some complications because it may already activate
    some cards so that the drivers can find them, and these tools can
    unconfigure them, or change their settings causing all sorts of nasty
    effects.
   
/etc/isdn
    ISDN configuration files.
   
/etc/issue
    Output by getty before the login prompt. Usually contains a short
    description or welcoming message to the system. The contents are up to
    the system administrator. Debian GNU/\s 3.0 \n \l
   
/etc/issue.net
    Presents the welcome screen to users who login remotely to your machine
    (whereas /etc/issue determines what a local user sees on login). Debian
    GNU/%s 3.0 %h
   
/etc/kde
    KDE initialization scripts and KDM configuration.
   
/etc/kde/kdm
    Location for the K Desktop Manager files. kdm manages a collection of X
    servers, which may be on the local host or remote machines. It provides
    services similar to those provided by init, getty, and login on
    character-based terminals: prompting for login name and password,
    authenticating the user, and running a session. kdm supports XDMCP (X
    Display Manager Control Protocol) and can also be used to run a chooser
    process which presents the user with a menu of possible hosts that offer
    XDMCP display management.
   
/etc/kderc
    System wide KDE initialization script. Commands here executed every time
    the KDE environment is loaded. It's a link to /etc/kde2/system.kdeglobals
   
   
          [Directories]                                                      
          dir_config=/etc/kde2                                               
          dir_html=/usr/share/doc/kde/HTML                                   
          dir_cgi=/usr/lib/cgi-bin                                           
          dir_apps=/usr/share/applnk                                         
          dir_mime=/usr/share/mimelnk                                        
          dir_services=/usr/share/services                                   
          dir_servicetypes=/usr/share/servicetypes                           
          [General]                                                          
          TerminalApplication=x-terminal-emulator                            
                                                                             
       
   
   
/etc/ld.so.conf, /etc/ld.so.cache
     
   
   
        /etc/ld.so.conf is a file containing a list of colon, space, tab,
        newline, or comma separated directories in which to search for
        libraries. /etc/ld.so.cache containing an ordered list of libraries
        found in the directories specified in /etc/ld.so.conf. This file is
        not in human readable format, and is not intended to be edited.
       
   
        'ldconfig' creates the necessary links and cache (for use by the
        run-time linker, ld.so) to the most recent shared libraries found in
        the directories specified on the command line, in the file /etc/
        ld.so.conf, and in the trusted directories (/usr/lib and /lib).
        'ldconfig' checks the header and file names of the libraries it
        encounters when determining which versions should have their links
        updated. ldconfig ignores symbolic links when scanning for libraries.
       
   
        'ldconfig' will attempt to deduce the type of ELF libs (ie. libc5 or
        libc6/glibc) based on what C libs if any the library was linked
        against, therefore when making dynamic libraries, it is wise to
        explicitly link against libc (use -lc).
       
   
        Some existing libs do not contain enough information to allow the
        deduction of their type, therefore the /etc/ld.so.conf file format
        allows the specification of an expected type. This is only used for
        those ELF libs which we can not work out. The format is like this
        "dirname=TYPE", where type can be libc4, libc5 or libc6. (This syntax
        also works on the command line). Spaces are not allowed. Also see the
        -p option.
       
   
        Directory names containing an = are no longer legal unless they also
        have an expected type specifier.
       
   
        'ldconfig' should normally be run by the super-user as it may require
        write permission on some root owned directories and files. It is
        normally run automatically at bootup or manually whenever new shared
        libraries are installed.
       
   
   
/usr/X11R6/lib
    X libraries.
   
/usr/local/lib
    Local libraries.
   
/etc/lilo.conf
    Configuration file for the Linux boot loader 'lilo'. 'lilo' is the
    original OS loader and can load Linux and others. The 'lilo' package
    normally contains lilo (the installer) and boot-record-images to install
    Linux, OS/2, DOS and generic Boot Sectors of other Oses. You can use Lilo
    to manage your Master Boot Record (with a simple text screen, text menu
    or colorful splash graphics) or call 'lilo' from other boot-loaders to
    jump-start the Linux kernel.
   
   
          Prompt #Prompt user to select                                             
          OS choice at boot timeout=300  # Amount of time to wait before default OS 
                                         # started (in ms)                          
          default=Debian4 #Default OS to be loaded                                  
          vga=normal #VGA mode                                                      
          boot=/dev/had #location of MBR                                            
          map=/boot/map #location of kernel                                         
          install=/boot/boot-bmp.b #File to be installed as boot sector             
          bitmap=/boot/debian.bmp #LILO boot image                                  
          bmp-table=30p,100p,1,10 #Colours                                          
          selectable bmp-colors=13,,0,1,,0 #Colours chosen                          
          lba32 #Required on most new systems to overcome                           
                #1024 cylinder problem                                              
          image=/vmlinuz #name of kernel                                            
          image label=Debian #a label                                               
          read-only #file system to be mounted read only                            
          root=/dev/hda6 #location of root filesystem                               
                                                                                    
          image=/boot/bzImage                                                       
          label=Debian4                                                             
          read-only                                                                 
          root=/dev/hda6                                                            
                                                                                    
          image=/mnt/redhat/boot/vmlinuz                                            
          label=Redhat                                                              
          initrd=/mnt/redhat/boot/initrd-2.4.18-14.img                              
          read-only                                                                 
          root=/dev/hda5                                                            
          vga=788                                                                   
          append=" hdc=ide-scsi hdd=ide-scsi"                                       
                                                                                    
          image=/mnt/mandrake/boot/vmlinuz                                          
          label="Mandrake"                                                          
          root=/dev/hda7                                                            
          initrd=/mnt/mandrake/boot/initrd.img                                      
          append="devfs=mount hdc=ide-scsi                                          
          acpi=off quiet"                                                           
          vga=788                                                                   
          read-only                                                                 
                                                                                    
          other=/dev/hda2                                                           
          table=/dev/hda                                                            
          loader=/boot/chain.b                                                      
          label=FBSD                                                                
          other=/dev/hda1                                                           
          label=Windows                                                             
          table=/dev/hda                                                            
                                                                                    
          other=/dev/fd0                                                            
          label=floppy unsafe                                                       
                                                                                    
       
   
   
/etc/local.gen
    This file lists locales that you wish to have built. You can find a list
    of valid supported locales at /usr/share/i18n/SUPPORTED. Other
    combinations are possible, but may not be well tested. If you change this
    file, you need to re-run locale-gen.
   
/etc/locale.alias
    Locale name alias data base.
   
/etc/login.defs
    Configuration control definitions for the login package. An inordinate
    number of attributes can be altered via this single file such as the
    location of mail, delay in seconds after a failed login, enabling display
    of fail log information, display of unknown username login failures,
    shell environment variables, etc....
   
/etc/logrotate.conf
    The logrotate utility is designed to simplify the administration of log
    files on a system which generates a lot of log files. Logrotate allows
    for the automatic rotation compression, removal and mailing of log files.
    Logrotate can be set to handle a log file daily, weekly, monthly or when
    the log file gets to a certain size. Normally, logrotate runs as a daily
    cron job.
   
      # see "man logrotate" for details                                      
      # rotate log files weekly                                              
      weekly                                                                 
                                                                             
      # keep 4 weeks worth of backlogs                                       
      rotate 4                                                               
                                                                             
      # create new (empty) log files after rotating old ones                 
      create                                                                 
                                                                             
      # uncomment this if you want your log files compressed                 
      #compress                                                              
                                                                             
      # packages drop log rotation information into this directory           
      include /etc/logrotate.d                                               
                                                                             
      # no packages own wtmp, or btmp -- we'll rotate them here              
      /var/log/wtmp {                                                        
          monthly                                                            
          create 0664 root utmp                                              
          rotate 1                                                           
      }                                                                      
                                                                             
      /var/log/btmp {                                                        
          missingok                                                          
          monthly                                                            
          create 0664 root utmp                                              
          rotate 1                                                           
      }                                                                      
                                                                             
      # system-specific logs may be configured here                          
   
/etc/ltrace.conf
    Configuration file for ltrace (Library Call Tracer). It tracks runtime
    library calls in dynamically linked programs. 'ltrace' is a debugging
    program which runs a specified command until it exits. While the command
    is executing, ltrace intercepts and records the dynamic library calls
    which are called by the executed process and the signals received by that
    process. It can also intercept and print the system calls executed by the
    program. The program to be traced need not be recompiled for this, so you
    can use it on binaries for which you don't have the source handy. You
    should install ltrace if you need a sysadmin tool for tracking the
    execution of processes.
   
/etc/magic
    Magic local data and configuration file for the file(1) command. Contains
    the descriptions of various file formats based on which file guesses the
    type of the file. Insert here your local magic data. Format is described
    in magic(5).
   
/etc/mail.rc
    Initialization file for 'mail'. 'mail' is an intelligent mail processing
    system which has a command syntax reminiscent of ed with lines replaced
    by messages. It's basically a command line version of Microsoft Outlook.
   
/etc/mailcap
    'metamail' capabilities file. The mailcap file is read by the metamail
    program to determine how to display non-text at the local site. The
    syntax of a mailcap file is quite simple, at least compared to termcap
    files. Any line that starts with "#" is a comment. Blank lines are
    ignored. Otherwise, each line defines a single mailcap entry for a single
    content type. Long lines may be continued by ending them with a backslash
    character, \. Each individual mailcap entry consists of a content-type
    specification, a command to execute, and (possibly) a set of optional
    "flag" values.
   
/etc/mailcap.order
    The mailcap ordering specifications. The order of entries in the /etc/
    mailcap file can be altered by editing the /etc/mailcap.order file. Each
    line of that file specifies a package and an optional mime type. Mailcap
    entries that match will be placed in the order of this file. Entries that
    don't match will be placed later.
   
/etc/mailname
    Mail server hostname. Normally the same as the hostname.
   
/etc/menu, /etc/menu-methods
    The menu package was inspired by the install-fvwm2-menu program from the
    old fvwm2 package. However, menu tries to provide a more general
    interface for menu building. With the update-menus command from this
    package, no package needs to be modified for every X window manager
    again, and it provides a unified interface for both text-and X-oriented
    programs.
   
    When a package that wants to add something to the menu tree gets
    installed, it will run update-menus in its postinstall script.
    Update-menus then reads in all menu files in /etc/menu/ /usr/lib/menu and
    /usr/lib/menu/default, and stores the menu entries of all installed
    packages in memory. Once that has been done, it will run the menu-methods
    in /etc/menu-methods/*, and pipe the information about the menu entries
    to the menu-methods on stdout, so that the menu-methods can read this.
    Each Window Manager or other program that wants to have the debian menu
    tree, will supply a menu-method script in /etc/menu-methods/. This
    menu-method then knows how to generate the startup-file for that window
    manager. To facilitate this task for the window-manager maintainers, menu
    provides a install-menu program. This program can generate the startup
    files for just about every window manager.
   
/etc/mgetty+sendfax
    Configuration files for use of mgetty as the interface on the serial
    port. The mgetty routine special routine has special features for
    handling things such as dial up connections and fax connections.
   
/etc/mime.types
    MIME-TYPES and the extensions that represent them. This file is part of
    the "mime-support" package. Note: Compression schemes like "gzip",
    "bzip", and "compress" are not actually "mime-types". They are
    "encodings" and hence must _not_ have entries in this file to map their
    extensions. The "mime-type" of an encoded file refers to the type of data
    that has been encoded, not the type of the encoding.
   
/etc/minicom
    'minicom' configuration files. 'minicom' is a communication program which
    somewhat resembles the shareware program TELIX but is free with source
    code and runs under most unices. Features include dialling directory with
    auto-redial, support for UUCP-style lock files on serial devices, a
    separate script language interpreter, capture to file, multiple users
    with individual configurations, and more.
   
/etc/modules
    List of modules to be loaded at startup.
   
      # /etc/modules: kernel modules to load at boot time.                   
      #                                                                      
      # This file should contain the names of kernel modules that are        
      # to be loaded at boot time, one per line. Comments begin with         
      # a "#", and everything on the line after them are ignored.            
      unix                                                                   
      af_packet                                                              
      via-rhine                                                              
      cmpci                                                                  
      ne2k-pci                                                               
      nvidia                                                                 
                                                                             
   
/etc/modules.conf
      ### This file is automatically generated by update-modules"                  
      #                                                                            
      # Please do not edit this file directly. If you want to change or add        
      # anything please take a look at the files in /etc/modutils and read         
      # the manpage for update-modules.                                            
      #                                                                            
      ### update-modules: start processing /etc/modutils/0keep                     
      # DO NOT MODIFY THIS FILE!                                                   
      # This file is not marked as conffile to make sure if you upgrade modutils   
      # it will be restored in case some modifications have been made.             
      #                                                                            
      # The keep command is necessary to prevent insmod and friends from ignoring  
      # the builtin defaults of a path-statement is encountered. Until all other   
      # packages use the new `add path'-statement this keep-statement is essential 
      # to keep your system working                                                
      keep                                                                         
                                                                                   
      ### update-modules: end processing /etc/modutils/0keep                       
                                                                                   
      ### update-modules: start processing /etc/modutils/actions                   
      # Special actions that are needed for some modules                           
                                                                                   
      # The BTTV module does not load the tuner module automatically,              
      # so do that in here                                                         
      post-install bttv insmod tuner                                               
      post-remove bttv rmmod tuner                                                 
                                                                                   
                                                                                   
      ### update-modules: end processing /etc/modutils/actions                     
                                                                                   
      ### update-modules: start processing /etc/modutils/aliases                   
      # Aliases to tell insmod/modprobe which modules to use                       
                                                                                   
      # Uncomment the network protocols you don't want loaded:                     
      # alias net-pf-1 off          # Unix                                         
      # alias net-pf-2 off          # IPv4                                         
      # alias net-pf-3 off          # Amateur Radio AX.25                          
      # alias net-pf-4 off          # IPX                                          
      # alias net-pf-5 off          # DDP / appletalk                              
      # alias net-pf-6 off          # Amateur Radio NET/ROM                        
      # alias net-pf-9 off          # X.25                                         
      # alias net-pf-10 off         # IPv6                                         
      # alias net-pf-11 off         # ROSE / Amateur Radio X.25 PLP                
      # alias net-pf-19 off         # Acorn Econet                                 
                                                                                   
      alias char-major-10-175       agpgart                                        
      alias char-major-10-200       tun                                            
      alias char-major-81   bttv                                                   
      alias char-major-108  ppp_generic                                            
      alias /dev/ppp                ppp_generic                                    
      alias tty-ldisc-3     ppp_async                                              
      alias tty-ldisc-14    ppp_synctty                                            
      alias ppp-compress-21 bsd_comp                                               
      alias ppp-compress-24 ppp_deflate                                            
      alias ppp-compress-26 ppp_deflate                                            
                                                                                   
      # Crypto modules (see http://www.kerneli.org/)                               
      alias loop-xfer-gen-0 loop_gen                                               
      alias loop-xfer-3     loop_fish2                                             
      alias loop-xfer-gen-10        loop_gen                                       
      alias cipher-2                des                                            
      alias cipher-3                fish2                                          
      alias cipher-4                blowfish                                       
      alias cipher-6                idea                                           
      alias cipher-7                serp6f                                         
      alias cipher-8                mars6                                          
      alias cipher-11               rc62                                           
      alias cipher-15               dfc2                                           
      alias cipher-16               rijndael                                       
      alias cipher-17               rc5                                            
                                                                                   
                                                                                   
      ### update-modules: end processing /etc/modutils/aliases                     
                                                                                   
      ### update-modules: start processing /etc/modutils/ltmodem-2.4.18            
      # lt_drivers: autoloading and insertion parameter usage                      
      alias char-major-62 lt_serial                                                
      alias /dev/tts/LT0  lt_serial                                                
      alias /dev/modem lt_serial                                                   
      # options lt_modem vendor_id=0x115d device_id=0x0420 Forced=3,0x130,0x2f8    
      # section for lt_drivers ends                                                
                                                                                   
      ### update-modules: end processing /etc/modutils/ltmodem-2.4.18              
                                                                                   
      ### update-modules: start processing /etc/modutils/paths                     
      # This file contains a list of paths that modprobe should scan,              
      # beside the once that are compiled into the modutils tools                  
      # themselves.                                                                
                                                                                   
                                                                                   
      ### update-modules: end processing /etc/modutils/paths                       
                                                                                   
      ### update-modules: start processing /etc/modutils/ppp                       
      alias /dev/ppp          ppp_generic                                          
      alias char-major-108    ppp_generic                                          
      alias tty-ldisc-3       ppp_async                                            
      alias tty-ldisc-14      ppp_synctty                                          
      alias ppp-compress-21   bsd_comp                                             
      alias ppp-compress-24   ppp_deflate                                          
      alias ppp-compress-26   ppp_deflate                                          
                                                                                   
      ### update-modules: end processing /etc/modutils/ppp                         
                                                                                   
      ### update-modules: start processing /etc/modutils/setserial                 
      #                                                                            
      # This is what I wanted to do, but logger is in /usr/bin, which isn't        
      # loaded when the module is first loaded into the kernel at boot time!       
      #                                                                            
      #post-install serial /etc/init.d/setserial start |                           
      #logger -p daemon.info -t "setserial-module reload"                          
      #pre-remove serial /etc/init.d/setserial stop |                              
      #logger -p daemon.info -t "setserial-module uload"                           
      #                                                                            
      alias /dev/tts          serial                                               
      alias /dev/tts/0        serial                                               
      alias /dev/tts/1        serial                                               
      alias /dev/tts/2        serial                                               
      alias /dev/tts/3        serial                                               
      post-install serial /etc/init.d/setserial modload > /dev/null 2> /dev/null   
      pre-remove serial /etc/init.d/setserial modsave  > /dev/null 2> /dev/null    
                                                                                   
      ### update-modules: end processing /etc/modutils/setserial                   
                                                                                   
      ### update-modules: start processing /etc/modutils/arch/i386                 
      alias parport_lowlevel parport_pc                                            
      alias char-major-10-144 nvram                                                
      alias binfmt-0064 binfmt_aout                                                
      alias char-major-10-135 rtc                                                  
                                                                                   
      ### update-modules: end processing /etc/modutils/arch/i386                   
                                                                                   
   
/etc/modutils
    These utilities are intended to make a Linux modular kernel manageable
    for all users, administrators and distribution maintainers.
   
/etc/mtools
    Debian default mtools configuration file. The mtools series of commands
    work with MS-DOS files and directories on floppy disks. This allows you
    to use Linux with MS-DOS formatted diskettes on DOS and Windows systems.
   
/etc/manpath.conf
    This file is used by the man_db package to configure the man and cat
    paths. It is also used to provide a manpath for those without one by
    examining their PATH environment variable. For details see the manpath(5)
    man page.
   
/etc/mediaprm
    Was formally named /etc/fdprm. See /etc/fdprm for further details.
   
/etc/motd
    The message of the day, automatically output after a successful login.
    Contents are up to the system administrator. Often used for getting
    information to every user, such as warnings about planned downtimes.
    Linux debian.localdomain.com 2.4.18 #1 Sat Mar 15 00:17:39 EST 2003 i686
    unknown Most of the programs included with the Debian GNU/Linux system
    are freely redistributable; the exact distribution terms for each program
    are described in the individual files in /usr/share/doc/*/copyright
    Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
    permitted by applicable law.
   
/etc/mtab
    List of currently mounted filesystems. Initially set up by the bootup
    scripts, and updated automatically by the mount command. Used when a list
    of mounted filesystems is needed, e.g., by the df command. This file is
    sometimes a symbolic link to /proc/mounts.
   
/etc/networks
    List of networks that the system is currently located on. For example,
    192.168.0.0.
   
/etc/nsswitch.conf
    System Database/Name Service Switch configuration file.
   
/etc/oss.conf
    OSS (Open Sound System) configuration file.
   
/etc/pam.d/
    This directory is the home of the configuration files for PAMs, Pluggable
    Authentication Modules.
   
/etc/postfix/
    Holds your postfix configuration files. Postfix is now the MTA of choice
    among Linux distributions. It is sendmail-compatible, offers improved
    speed over sendmail, ease of administration and security. It was
    originally developed by IBM and was called the IBM Secure Mailer and is
    used in many large commercial networks. It is now the de-facto standard.
   
/etc/ppp/
    The place where your dial-up configuration files are placed. More than
    likely to be created by the text menu based pppconfig or other GUI based
    ppp configuration utilities such as kppp or gnome-ppp.
   
/etc/pam.conf
    Most programs use a file under the /etc/pam.d/ directory to setup their
    PAM service modules. This file is and can be used, but is not
    recommended.
   
/etc/paper.config
    Paper size configuration file.
   
/etc/papersize
    Default papersize.
   
/etc/passwd
    This is the 'old' password file, It is kept for compatibility and
    contains the user database, with fields giving the username, real name,
    home directory, encrypted password, and other information about each
    user. The format is documented in the passwd man(ual) page.
   
    root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/bin/sh      
    bin:x:2:2:bin:/bin:/bin/sh sys:x:3:3:sys:/dev:/bin/sh                      
    sync:x:4:100:sync:/bin:/bin/sync games:x:5:100:games:/usr/games:/bin/sh    
    man:x:6:100:man:/var/cache/man:/bin/sh lp:x:7:7:lp:/var/spool/lpd:/bin/sh  
    mail:x:8:8:mail:/var/mail:/bin/sh news:x:9:9:news:/var/spool/news:/bin/sh  
    uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh proxy:x:13:13:proxy:/bin:/bin/sh 
    postgres:x:31:32:postgres:/var/lib/postgres:/bin/sh                        
    www-data:x:33:33:www-data:/var/www:/bin/sh                                 
    backup:x:34:34:backup:/var/backups:/bin/sh                                 
    operator:x:37:37:Operator:/var:/bin/sh                                     
    list:x:38:38:SmartList:/var/list:/bin/sh irc:x:39:39:ircd:/var:/bin/sh     
    gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh    
    nobody:x:65534:65534:nobody:/home:/bin/sh                                  
    binh:x:1000:1000:,,,:/home/binh:/bin/bash                                  
    identd:x:100:65534::/var/run/identd:/bin/false                             
    sshd:x:101:65534::/var/run/sshd:/bin/false gdm:x:102:101:Gnome Display     
    Manager:/var/lib/gdm:/bin/false                                            
    telnetd:x:103:103::/usr/lib/telnetd:/bin/false                             
    dummy:x:1001:1001:,,,:/home/dummy:/bin/bash                                
   
/etc/passwd-
    Old /etc/passwd file.
   
/etc/printcap
    Printer configuration (capabilities) file. The definition of all system
    printers, whether local or remote, is stored in this file. Its layout is
    similar to that of /etc/termcap but it uses a different syntax.
   
/etc/profile
    Files and commands to be executed at login or startup time by the Bourne
    or C shells. These allow the system administrator to set global defaults
    for all users.
   
/etc/profile.d
    Shells scripts to be executed upon login to the Bourne or C shells. These
    scripts are normally called from the /etc/profile file.
   
/etc/protocols
    Protocols definitions file. It describes the various DARPA Internet
    protocols that are available from the TCP/IP subsystem. It should be
    consulted instead of using the numbers in the ARPA include files or
    resorting to guesstimation. This file should be left untouched since
    changes could result in incorrect IP packages.
   
/etc/pcmcia
    Configuration files for PCMCIA devices. Generally only useful to laptop
    users.
   
/etc/reportbug.conf
    Configuration file for reportbug. Reportbug is primarily designed to
    report bugs in the Debian distribution. By default it creates an e-mail
    to the Debian bug tracking system at mit@bugs.debian.org with information
    about the bug. Using the -bts option you can report bugs to other servers
    also using ddebbugs such as KDE.org. It is similar to bug but has far
    greater capabilities while still maintaining simplicity.
   
/etc/rc.boot or /etc/rc?.d
    These directories contain all the files necessary to control system
    services and configure runlevels. A skeleton file is provided in /etc/
    init.d/skeleton
   
/etc/rcS.d
    The scripts in this directory are executed once when booting the system,
    even when booting directly into single user mode. The files are all
    symbolic links, the real files are located in /etc/init.d/. For a more
    general discussion of this technique, see /etc/init.d/README.
   
/etc/resolv.conf
    Configuration of how DNS is to occur is defined in this file. It tells
    the name resolver libraries where they need to go to find information not
    found in the /etc/hosts file. This always has at least one nameserver
    line, but preferably three. The resolver uses each in turn. More than the
    first three can be included but anything beyond the first three will be
    ignored. Two lines that appear in the /etc/resolv.conf file are domain
    and search. Both of these are mutually exclusive options, and where both
    show up, the last one wins. Other entries beyond the three discussed here
    are listed in the man pages but aren't often used.
   
/etc/rmt
    This is not a mistake. This shell script (/etc/rmt) has been provided for
    compatibility with other Unix-like systems, some of which have utilities
    that expect to find (and execute) rmt in the /etc directory on remote
    systems.
   
/etc/rpc
    The rpc file contains user readable names that can be used in place of
    rpc program numbers. Each line has the following information: -name of
    server for the rpc program -rpc program number -aliases Items are
    separated by any number of blanks and/or tab characters. A ``#''
    indicates the beginning of a comment; characters up to the end of the
    line are not interpreted by routines which search the file.
   
      # /etc/rpc:                                                            
      # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $                   
      #                                                                      
      # rpc 88/08/01 4.0 RPCSRC; from 1.12   88/02/07 SMI                    
                                                                             
      portmapper    100000  portmap sunrpc                                   
      rstatd                100001  rstat rstat_svc rup perfmeter            
      rusersd               100002  rusers                                   
      nfs           100003  nfsprog                                          
      ypserv                100004  ypprog                                   
      mountd                100005  mount showmount                          
      ypbind                100007                                           
      walld         100008  rwall shutdown                                   
      yppasswdd     100009  yppasswd                                         
      etherstatd    100010  etherstat                                        
      rquotad               100011  rquotaprog quota rquota                  
      sprayd                100012  spray                                    
      3270_mapper   100013                                                   
      rje_mapper    100014                                                   
      selection_svc 100015  selnsvc                                          
      database_svc  100016                                                   
      rexd          100017  rex                                              
      alis          100018                                                   
      sched         100019                                                   
      llockmgr      100020                                                   
      nlockmgr      100021                                                   
      x25.inr               100022                                           
      statmon               100023                                           
      status                100024                                           
      bootparam     100026                                                   
      ypupdated     100028  ypupdate                                         
      keyserv               100029  keyserver                                
      tfsd          100037                                                   
      nsed          100038                                                   
      nsemntd               100039                                           
      pcnfsd                150001                                           
      amd           300019  amq                                              
      sgi_fam               391002                                           
      ugidd         545580417                                                
      bwnfsd          788585389                                              
                                                                             
   
/etc/samba
    Samba configuration files. A 'LanManager' like file and printer server
    for Unix. The Samba software suite is a collection of programs that
    implements the SMB protocol for unix systems, allowing you to serve files
    and printers to Windows, NT, OS/2 and DOS clients. This protocol is
    sometimes also referred to as the LanManager or NetBIOS protocol.
   
/etc/sane.d
    Sane configuration files. SANE stands for "Scanner Access Now Easy" and
    is an application programming interface (API) that provides standardized
    access to any raster image scanner hardware (flatbed scanner, hand-held
    scanner, video- and still-cameras, frame-grabbers, etc.). The SANE API is
    public domain and its discussion and development is open to everybody.
    The current source code is written for UNIX (including GNU/Linux) and is
    available under the GNU General Public License (the SANE API is available
    to proprietary applications and backends as well, however).
   
    SANE is a universal scanner interface. The value of such a universal
    interface is that it allows writing just one driver per image acquisition
    device rather than one driver for each device and application. So, if you
    have three applications and four devices, traditionally you'd have had to
    write 12 different programs. With SANE, this number is reduced to seven:
    the three applications plus the four drivers. Of course, the savings get
    even bigger as more and more drivers and/or applications are added.
   
    Not only does SANE reduce development time and code duplication, it also
    raises the level at which applications can work. As such, it will enable
    applications that were previously unheard of in the UNIX world. While
    SANE is primarily targeted at a UNIX environment, the standard has been
    carefully designed to make it possible to implement the API on virtually
    any hardware or operating system.
   
    While SANE is an acronym for ``Scanner Access Now Easy'' the hope is of
    course that SANE is indeed sane in the sense that it will allow easy
    implementation of the API while accommodating all features required by
    today's scanner hardware and applications. Specifically, SANE should be
    broad enough to accommodate devices such as scanners, digital still and
    video cameras, as well as virtual devices like image file filters.
   
    If you're familiar with TWAIN, you may wonder why there is a need for
    SANE. Simply put, TWAIN does not separate the user-interface from the
    driver of a device. This, unfortunately, makes it difficult, if not
    impossible, to provide network transparent access to image acquisition
    devices (which is useful if you have a LAN full of machines, but scanners
    connected to only one or two machines; it's obviously also useful for
    remote-controlled cameras and such). It also means that any particular
    TWAIN driver is pretty much married to a particular GUI API (be it Win32
    or the Mac API). In contrast, SANE cleanly separates device controls from
    their representation in a user-interface. As a result, SANE has no
    difficulty supporting command-line driven interfaces or
    network-transparent scanning. For these reasons, it is unlikely that
    there will ever be a SANE backend that can talk to a TWAIN driver. The
    converse is no problem though: it would be pretty straight forward to
    access SANE devices through a TWAIN source. In summary, if TWAIN had been
    just a little better designed, there would have been no reason for SANE
    to exist, but things being the way they are, TWAIN simply isn't SANE.
   
/etc/securetty
    Identifies secure terminals, i.e., the terminals from which root is
    allowed to log in. Typically only the virtual consoles are listed, so
    that it becomes impossible (or at least harder) to gain superuser
    privileges by breaking into a system over a modem or a network.
   
   
                                                                                 
          # /etc/securetty: list of terminals on which root is allowed to login. 
          # See securetty(5) and login(1).                                       
          console                                                                
                                                                                 
          # Standard consoles                                                    
          tty1                                                                   
          tty2                                                                   
          tty3                                                                   
          tty4                                                                   
          tty5                                                                   
          tty6                                                                   
          tty7                                                                   
          tty8                                                                   
          tty9                                                                   
          tty10                                                                  
          tty11                                                                  
          tty12                                                                  
                                                                                 
          # Same as above, but these only occur with devfs devices               
          vc/1                                                                   
          vc/2                                                                   
          vc/3                                                                   
          vc/4                                                                   
          vc/5                                                                   
          vc/6                                                                   
          vc/7                                                                   
          vc/8                                                                   
          vc/9                                                                   
          vc/10                                                                  
          vc/11                                                                  
          vc/12                                                                  
                                                                                 
       
   
   
/etc/sensors.conf
    Configuration file for libsensors. A set of libraries designed to
    ascertain current hardware states via motherboard sensor chips. Useful
    statistics such as core voltages, CPU temperature can be determined
    through third party utilities that make user of these libraries such as
    'gkrellm'. If you do not wish to install these packages you may also
    utilise the /proc filesystem real-time nature.
   
/etc/sudoers
    Sudoers file. This file must be edited with the 'visudo' command as root.
    The sudo command allows an authenticated user to execute an authorized
    command as root. Both the effective UID and GID are set to 0 (you are
    basically root). It determines which users are authorized and which
    commands they are authorized to use. Configuration of this command is via
    this file.
   
/etc/shadow
    Shadow password file on systems with shadow password software installed
    (PAMs). Shadow passwords move the encrypted password from /etc/passwd
    into /etc/shadow; the latter is not readable by anyone except root. This
    makes it more difficult to crack passwords.
   
/etc/shadow-
    Old /etc/shadow file.
   
/etc/sysctl.conf
    Configuration file for setting system variables, most notably kernel
    parameters. 'sysctl' is a means of configuring certain aspects of the
    kernel at run-time, and the /proc/sys/ directory is there so that you
    don't even need special tools to do it!
   
/etc/security
    Essential to security. This subdirectory allows administrators to impose
    quota limits, access limits and also to configure PAM environments.
   
/etc/serial.conf
    Serial port configuration. Changeable parameters include speed, baud
    rate, port, irq and type.
   
/etc/services
    A definition of the networks, services and the associated port for each
    protocol that are available on this system. For example, web services
    (http) are assigned to port 80 by default. # /etc/services: # $Id:
    etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $ # # Network services,
    Internet style # # Note that it is presently the policy of IANA to assign
    a single # well-known port number for both TCP and UDP; hence, most
    entries # here have two entries even if the protocol doesn't support UDP
    # operations. Updated from RFC 1700, ``Assigned Numbers'' (October #
    1994). Not all ports are included, only the more common ones. echo 7/tcp
    echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp
    users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp
    18/tcp # message send protocol msp 18/udp # message send protocol chargen
    19/tcp ttytst source chargen 19/udp ttytst source ftp-data 20/tcp ftp 21/
    tcp fsp 21/udp fspd ssh 22/tcp # SSH Remote Login Protocol ssh 22/udp #
    SSH Remote Login Protocol telnet 23/tcp # 24 - private smtp 25/tcp mail #
    26 - unassigned time 37/tcp timserver time 37/udp timserver rlp 39/udp
    resource # resource location nameserver 42/tcp name # IEN 116 whois 43/
    tcp nicname re-mail-ck 50/tcp # Remote Mail Checking Protocol re-mail-ck
    50/udp # Remote Mail Checking Protocol domain 53/tcp nameserver #
    name-domain server domain 53/udp nameserver netbios-ns 137/tcp # NETBIOS
    Name Service netbios-ns 137/udp netbios-dgm 138/tcp # NETBIOS Datagram
    Service netbios-dgm 138/udp netbios-ssn 139/tcp # NETBIOS session service
    netbios-ssn 139/udp x11 6000/tcp x11-0 # X windows system x11 6000/udp
    x11-0 # X windows system
   
/etc/shells
    Lists trusted shells. The chsh command allows users to change their login
    shell only to shells listed in this file. ftpd, the server process that
    provides FTP services for a machine, will check that the user's shell is
    listed in /etc/shells and will not let people log in unless the shell is
    listed there. There are also some display managers that will passively or
    actively (dependent upon on distribution and display manager being used)
    refuse a user access to the system unless their shell is one of those
    listed here.
   
   
          # /etc/shells: valid login shells                                  
          /bin/ash                                                           
          /bin/bash                                                          
          /bin/csh                                                           
          /bin/sh                                                            
          /usr/bin/es                                                        
          /usr/bin/ksh                                                       
          /bin/ksh                                                           
          /usr/bin/rc                                                        
          /usr/bin/tcsh                                                      
          /bin/tcsh                                                          
          /usr/bin/zsh                                                       
          /bin/sash                                                          
          /bin/zsh                                                           
          /usr/bin/esh                                                       
                                                                             
       
   
   
/etc/skel/
    The default files for each new user are stored in this directory. Each
    time a new user is added, these skeleton files are copied into their home
    directory. An average system would have: .alias, .bash_profile, .bashrc
    and .cshrc files. Other files are left up to the system administrator.
   
/etc/sysconfig/
    This directory contains configuration files and subdirectories for the
    setup of system configuration specifics and for the boot process, like
    'clock', which sets the timezone, or 'keyboard' which controls the
    keyboard map. The contents may vary drastically depending on which
    distribution and what utilities you have installed. For example, on a
    Redhat or Mandrake based system it is possible to alter an endless array
    of attributes from the default desktop to whether DMA should be enabled
    for your IDE devices. On our Debian reference system though this folder
    is almost expedient containing only two files hwconf and soundcard which
    are both configured by the Redhat utilities hwconf and sndconfig
    respectively.
   
/etc/slip
    Configuration files for the setup and operation of SLIP (serial line IP)
    interface. Generally unused nowadays. This protocol has been superceded
    by the faster and more efficient PPP protocol.
   
/etc/screenrc
    This is the system wide screenrc. You can use this file to change the
    default behavior of screen system wide or copy it to ~/.screenrc and use
    it as a starting point for your own settings. Commands in this file are
    used to set options, bind screen functions to keys, redefine terminal
    capabilities, and to automatically establish one or more windows at the
    beginning of your screen session. This is not a comprehensive list of
    options, look at the screen manual for details on everything that you can
    put in this file.
   
/etc/scrollkeeper.conf
    A free electronic cataloging system for documentation. It stores metadata
    specified by the http://www.ibiblio.org/osrt/omf/ (Open Source Metadata
    Framework) as well as certain metadata extracted directly from documents
    (such as the table of contents). It provides various functionality
    pertaining to this metadata to help browsers, such as sorting the
    registered documents or searching the metadata for documents which
    satisfy a set of criteria.
   
/etc/ssh
    'ssh' configuration files. 'ssh' is a secure rlogin/rsh/rcp replacement
    (OpenSSH). This is the portable version of OpenSSH, a free implementation
    of the Secure Shell protocol as specified by the IETF secsh working
    group. 'ssh' (Secure Shell) is a program for logging into a remote
    machine and for executing commands on a remote machine. It provides
    secure encrypted communications between two untrusted hosts over an
    insecure network. X11 connections and arbitrary TCP/IP ports can also be
    forwarded over the secure channel. It is intended as a replacement for
    rlogin, rsh and rcp, and can be used to provide applications with a
    secure communication channel. It should be noted that in some countries,
    particularly Iraq, and Pakistan, it may be illegal to use any encryption
    at all without a special permit.
   
/etc/syslog.conf
    Lists where log files should go, what messages are written to them and
    the level of verbosity. It is also now possible to filter based on
    message content, message integrity, message encryption (near future),
    portability and better network forwarding.
   
/etc/termcap
    The terminal capability database. Describes the "escape sequences" by
    which various terminals can be controlled. Programs are written so that
    instead of directly outputting an escape sequence that only works on a
    particular brand of terminal, they look up the correct sequence to do
    whatever it is they want to do in /etc/termcap. As a result most programs
    work with most kinds of terminals.
   
/etc/timezone
    local timezone.
   
/etc/updatedb.conf
    Sets environment variables that are used by updatedb which therefore
    configures the database for 'locate', a utility that locates a pattern in
    a database of filenames and returns the filenames that match.
   
      # This file sets environment variables which are used by updatedb            
                                                                                   
      # filesystems which are pruned from updatedb database                        
      PRUNEFS="NFS nfs afs proc smbfs autofs auto iso9660 ncpfs coda devpts ftpfs" 
      export PRUNEFS                                                               
      # paths which are pruned from updatedb database                              
      PRUNEPATHS="/tmp /usr/tmp /var/tmp /afs /amd /alex /var/spool"               
      export PRUNEPATHS                                                            
      # netpaths which are added                                                   
      NETPATHS=""                                                                  
      export NETPATHS                                                              
                                                                                   
   
/etc/vga
    The configuration file for the svgalib is stored in this directory.
    svgalib provides graphics capabilities to programs running on the system
    console, without going through the X Window System. It uses direct access
    to the video hardware to provide low-level access to the standard VGA and
    SVGA graphics modes. It only works with some video hardware; so use with
    caution.
   
/etc/vim
    Contains configuration files for both vim and its X based counterpart
    gvim. A wide range of options can be accessed though these two files such
    as automatic indentation, syntax highlighting, etc....
   
/etc/xinetd.d/
    The original 'inetd' daemon has now been superceded by the much improved
    'xinetd'. 'inetd' should be run at boot time by /etc/init.d/inetd (or /
    etc/rc.local on some systems). It then listens for connections on certain
    Internet sockets. When a connection is found on one of its sockets, it
    decides what service the socket corresponds to, and invokes a program to
    service the request. After the program is finished, it continues to
    listen on the socket (except in some cases). Essentially, inetd allows
    running one daemon to invoke several others, reducing load on the system.
    Services controlled via xinetd put their configuration files here.
   
/etc/zlogin
    System-wide .zlogin file for zsh(1). This file is sourced only for login
    shells. It should contain commands that should be executed only in login
    shells. It should be used to set the terminal type and run a series of
    external commands (fortune, msgs, from, etc.)
   
/etc/zlogout
    Commands to be executed upon user exit from the zsh. Its control is
    system-wide but the .zlogout file for zsh(1) does override it in terms of
    importance.
   
/etc/zprofile
    System-wide .zprofile file for zsh(1). This file is sourced only for
    login shells (i.e. Shells invoked with "-" as the first character of argv
    [0], and shells invoked with the -l flag.)
   
/etc/zshenv
    System-wide .zshenv file for zsh(1). This file is sourced on all
    invocations of the shell. If the -f flag is present or if the NO_RCS
    option is set within this file, all other initialization files are
    skipped. This file should contain commands to set the command search
    path, plus other important environment variables. This file should not
    contain commands that produce output or assume the shell is attached to a
    tty.
   
/etc/zshrc
    System-wide .zshrc file for zsh(1). This file is sourced only for
    interactive shells. It should contain commands to set up aliases,
    functions, options, key bindings, etc.
   

Compliance with the FSSTND requires that the following directories, or
symbolic links to directories are required in /etc:

  opt       Configuration for /opt                                                
  X11       Configuration for the X Window system (optional)                      
  sgml      Configuration for SGML (optional)                                     
  xml       Configuration for XML (optional)                                      
                                                                                  
  The following directories, or symbolic links to directories must be in /etc,    
  if the corresponding subsystem is installed:                                    
                                                                                  
  opt       Configuration for /opt                                                
                                                                                  
  The following files, or symbolic links to files, must be in /etc if the         
  corresponding subsystem is installed (it is recommended that files be           
  stored in subdirectories of /etc/ rather than directly in /etc:                 
                                                                                  
  csh.login   Systemwide initialization file for C shell logins (optional)        
  exports     NFS filesystem access control list (optional)                       
  fstab       Static information about filesystems (optional)                     
  ftpusers    FTP daemon user access control list (optional)                      
  gateways    File which lists gateways for routed (optional)                     
  gettydefs   Speed and terminal settings used by getty (optional)                
  group       User group file (optional)                                          
  host.conf   Resolver configuration file (optional)                              
  hosts       Static information about host names (optional)                      
  hosts.allow Host access file for TCP wrappers (optional)                        
  hosts.deny  Host access file for TCP wrappers (optional)                        
  hosts.equiv List of trusted hosts for rlogin, rsh, rcp (optional)               
  hosts.lpd   List of trusted hosts for lpd (optional)                            
  inetd.conf  Configuration file for inetd (optional)                             
  inittab     Configuration file for init (optional)                              
  issue       Pre-login message and identification file (optional)                
  ld.so.conf  List of extra directories to search for shared libraries            
              (optional)                                                          
  motd        Post-login message of the day file (optional)                       
  mtab        Dynamic information about filesystems (optional)                    
  mtools.conf Configuration file for mtools (optional)                            
  networks    Static information about network names (optional)                   
  passwd      The password file (optional)                                        
  printcap    The lpd printer capability database (optional)                      
  profile     Systemwide initialization file for sh shell logins (optional)       
  protocols   IP protocol listing (optional)                                      
  resolv.conf Resolver configuration file (optional)                              
  rpc         RPC protocol listing (optional)                                     
  securetty   TTY access control for root login (optional)                        
  services    Port names for network services (optional)                          
  shells      Pathnames of valid login shells (optional)                          
  syslog.conf Configuration file for syslogd (optional)                           
                                                                                  
  mtab does not fit the static nature of /etc: it is excepted for historical      
  reasons. On some Linux systems, this may be a symbolic link to /proc/mounts,    
  in which case this exception is not required.                                   
                                                                                  
  /etc/opt : Configuration files for /opt                                         
  Host-specific configuration files for add-on application software packages      
  must be installed within the directory /etc/opt/&60;subdir&62;, where           
  &60;subdir&62; is the name of the subtree in /opt where the static data         
  from that package is stored.                                                    
                                                                                  
  No structure is imposed on the internal arrangement of /etc/opt/&60;subdir&62;. 
  If a configuration file must reside in a different location in order for the    
  package or system to function properly, it may be placed in a location other    
  than /etc/opt/&60;subdir&62;.                                                   
                                                                                  
  The rationale behind this subtree is best explained by refering to the          
  rationale for /opt.                                                             
                                                                                  
  /etc/X11 : Configuration for the X Window System (optional)                     
  /etc/X11 is the location for all X11 host-specific configuration. This          
  directory is necessary to allow local control if /usr is mounted read only.     
                                                                                  
  The following files, or symbolic links to files, must be in /etc/X11 if the     
  corresponding subsystem is installed:                                           
                                                                                  
  Xconfig    The configuration file for early versions of XFree86 (optional)      
  XF86Config The configuration file for XFree86 versions 3 and 4 (optional)       
  Xmodmap    Global X11 keyboard modification file (optional)                     
                                                                                  
  Subdirectories of /etc/X11 may include those for xdm and for any other          
  programs (some window managers, for example) that need them.                    
                                                                                  
  /etc/X11/xdm holds the configuration files for xdm. These are most of the       
  files previously found in /usr/lib/X11/xdm. Some local variable data for        
  xdm is stored in /var/lib/xdm.                                                  
                                                                                  
  It is recommended that window managers with only one configuration file         
  which is a default .*wmrc file must name it system.*wmrc (unless there is       
  a widely-accepted alternative name) and not use a subdirectory. Any window      
  manager subdirectories must be identically named to the actual window           
  manager binary.                                                                 
                                                                                  
  /etc/sgml : Configuration files for SGML (optional)                             
  Generic configuration files defining high-level parameters of the SGML          
  systems are installed here. Files with names *.conf indicate generic            
  configuration files. File with names *.cat are the DTD-specific centralized     
  catalogs, containing references to all other catalogs needed to use the         
  given DTD. The super catalog file catalog references all the centralized        
  catalogs.                                                                       
                                                                                  
  /etc/xml : Configuration files for XML (optional)                               
  Generic configuration files defining high-level parameters of the XML           
  systems are installed here. Files with names *.conf indicate generic            
  configuration files. The super catalog file catalog references all the          
  centralized catalogs.                                                           
                                                                                  
-----------------------------------------------------------------------------

1.7. /home

Linux is a multi-user environment so each user is also assigned a specific
directory that is accessible only to them and the system administrator. These
are the user home directories, which can be found under '/home/$USER' (~/).
It is your playground: everything is at your command, you can write files,
delete them, install programs, etc.... Your home directory contains your
personal configuration files, the so-called dot files (their name is preceded
by a dot). Personal configuration files are usually 'hidden', if you want to
see them, you either have to turn on the appropriate option in your file
manager or run ls with the -a switch. If there is a conflict between personal
and system wide configuration files, the settings in the personal file will
prevail.

Dotfiles most likely to be altered by the end user are probably your
.xsession and .bashrc files. The configuration files for X and Bash
respectively. They allow you to be able to change the window manager to be
startup upon login and also aliases, user-specified commands and environment
variables respectively. Almost always when a user is created their dotfiles
will be taken from the /etc/skel directory where system administrators place
a sample file that user's can modify to their hearts content.

/home can get quite large and can be used for storing downloads, compiling,
installing and running programs, your mail, your collection of image or sound
files etc.

The FSSTND states that:

  /home is a fairly standard concept, but it is clearly a site-specific      
  filesystem.                                                                
                                                                             
  Different people prefer to place user accounts in a variety of places.     
  This section describes only a suggested placement for user home            
  directories; nevertheless we recommend that all FHS-compliant              
  distributions use this as the default location for home directories.       
  On small systems, each user's directory is typically one of the many       
  subdirectories of /home such as /home/smith, /home/torvalds,               
  /home/operator, etc. On large systems (especially when the /home           
  directories are shared amongst many hosts using NFS) it is useful          
  to subdivide user home directories. Subdivision may be accomplished by     
  using subdirectories such as /home/staff, /home/guests, /home/students,    
  etc.                                                                       
                                                                             
  The setup will differ from host to host. Therefore, no program             
  should rely on this location.                                              
                                                                             
  If you want to find out a user's home directory, you should use the        
  getpwent(3) library function rather than relying on /etc/passwd because    
  user information may be stored remotely using systems such as NIS.         
                                                                             
  User specific configuration files for applications are stored in the       
  user's home directory in a file that starts with the '.' character         
  (a "dot file"). If an application needs to create more than one dot        
  file then they should be placed in a subdirectory with a name starting     
  with a '.' character, (a "dot directory"). In this case the                
  configuration files should not start with the '.' character.               
                                                                             
  It is recommended that apart from autosave and lock files programs         
  should refrain from creating non dot files or directories in a home        
  directory without user intervention.                                       
                                                                             
-----------------------------------------------------------------------------

1.8. /initrd

 
initrd provides the capability to load a RAM disk by the boot                
loader. This RAM disk can then be mounted as the root file                   
system and programs can be run from it. Afterwards, a new                    
root file system can be mounted from a different device. The                 
previous root (from initrd) is then moved to a directory and                 
can be subsequently unmounted.                                               
                                                                             
initrd is mainly designed to allow system startup to occur                   
in two phases, where the kernel comes up with a minimum set                  
of compiled-in drivers, and where additional modules are                     
loaded from initrd.                                                          
                                                                             
Operation                                                                    
---------                                                                    
                                                                             
When using initrd, the system typically boots as follows:                    
                                                                             
 1) the boot loader loads the kernel and the initial RAM disk                
 2) the kernel converts initrd into a "normal" RAM disk and                  
    frees the memory used by initrd                                          
 3) initrd is mounted read-write as root                                     
 4) /linuxrc is executed (this can be any valid executable,                  
 including shell scripts; it is run with uid 0 and can do                    
 basically everything init can do)                                           
 5) linuxrc mounts the "real" root file system                               
 6) linuxrc places the root file system at the root directory                
    using the pivot_root system call                                         
 7) the usual boot sequence (e.g. invocation of /sbin/init) is               
    performed on the root file system                                        
 8) the initrd file system is removed                                        
                                                                             
Note that changing the root directory does not involve unmounting            
it. It is therefore possible to leave processes running on initrd            
during that procedure. Also note that file systems mounted under             
initrd continue to be accessible.                                            
                                                                             
Usage scenarios                                                              
---------------                                                              
                                                                             
The main motivation for implementing initrd was to allow                     
for modular kernel configuration at system installation.                     
The procedure would work as follows:                                         
                                                                             
 1) system boots from floppy or other media with a minimal kernel            
    (e.g. support for RAM disks, initrd, a.out, and the Ext2 FS)             
    and loads initrd                                                         
 2) /linuxrc determines what is needed to (1) mount the "real" root          
    FS (i.e. device type, device drivers, file system) and (2) the           
    distribution media (e.g. CD-ROM, network, tape, ...). This can           
    be done by asking the user, by auto-probing, or by using a               
    hybrid approach.                                                         
 3) /linuxrc loads the necessary kernel modules                              
 4) /linuxrc creates and populates the root file system (this                
    doesn't have to be a very usable system yet)                             
 5) /linuxrc invokes pivot_root to change the root file system and           
    execs - via chroot - a program that continues the installation           
 6) the boot loader is installed                                             
 7) the boot loader is configured to load an initrd with the set of          
    modules that was used to bring up the system (e.g. /initrd can           
    be modified, then unmounted, and finally, the image is written           
    from /dev/ram0 or /dev/rd/0 to a file)                                   
 8) now the system is bootable and additional installation tasks             
    can be performed                                                         
                                                                             
The key role of initrd here is to re-use the configuration data              
during normal system operation without requiring the use of a                
bloated "generic" kernel or re-compiling or re-linking the kernel.           
                                                                             
A second scenario is for installations where Linux runs on systems           
with different hardware configurations in a single administrative            
domain. In such cases, it is desirable to generate only a small set          
of kernels (ideally only one) and to keep the system-specific part           
of configuration information as small as possible. In this case, a           
common initrd could be generated with all the necessary modules.             
Then, only /linuxrc or a file read by it would have to be different.         
                                                                             
A third scenario are more convenient recovery disks, because                 
information like the location of the root FS partition doesn't have          
to be provided at boot time, but the system loaded from initrd can           
invoke a user-friendly dialog and it can also perform some sanity            
checks (or even some form of auto-detection).                                
                                                                             
Last not least, CD-ROM distributors may use it for better installation       
from CD, e.g. by using a boot floppy and bootstrapping a bigger RAM disk     
via initrd from CD; or by booting via a loader like LOADLIN or directly      
from the CD-ROM, and loading the RAM disk from CD without need of floppies.  
-----------------------------------------------------------------------------

1.9. /lib

 The /lib directory contains kernel modules and those shared library images
(the C programming code library) needed to boot the system and run the
commands in the root filesystem, ie. by binaries in /bin and /sbin. Libraries
are readily identifiable through their filename extension of *.so. Windows
equivalent to a shared library would be a DLL (dynamically linked library)
file. They are essential for basic system functionality. Kernel modules
(drivers) are in the subdirectory /lib/modules/'kernel-version'. To ensure
proper module compilation you should ensure that /lib/modules/
'kernel-version'/kernel/build points to /usr/src/'kernel-version' or ensure
that the Makefile knows where the kernel source itself are located.

 

/lib/'machine-architecture'
    Contains platform/architecture dependent libraries.
   
/lib/iptables
    iptables shared library files.
   
/lib/kbd
    Contains various keymaps.
   
/lib/modules/'kernel-version'
    The home of all the kernel modules. The organisation of files here is
    reasonably clear so no requires no elaboration.
   
/lib/modules/'kernel-version'/isapnpmap.dep
      has details on ISA based cards, the modules that they require and
    various other attributes.
   
/lib/modules/'kernel-version'/modules.dep
      lists all modules dependencies. This file can be updated using the
    depmod command.
   
/lib/modules/'kernel-version'/pcimap
    is the PCI equivalent of the /lib/modules/'kernel-version'/isapnpmap.dep
    file.
   
/lib/modules/'kernel-version'/usbmap
    is the USB equivalent of the /lib/modules/'kernel-version'/isapnpmap.dep
    file.
   
/lib/oss
      All OSS (Open Sound System) files are installed here by default.
   
/lib/security
    PAM library files.
   

 
The FSSTND states that the /lib directory contains those shared library        
images needed to boot the system and run the commands in the root filesystem,  
ie. by binaries in /bin and /sbin.                                             
                                                                               
Shared libraries that are only necessary for binaries in /usr (such as any     
X Window binaries) must not be in /lib. Only the shared libraries required     
to run binaries in /bin and /sbin may be here. In particular, the library      
libm.so.* may also be placed in /usr/lib if it is not required by anything     
in /bin or /sbin.                                                              
                                                                               
At least one of each of the following filename patterns are required (they     
may be files, or symbolic links):                                              
                                                                               
libc.so.* The dynamically-linked C library (optional)                          
ld*       The execution time linker/loader (optional)                          
                                                                               
If a C preprocessor is installed, /lib/cpp must be a reference to it, for      
historical reasons. The usual placement of this binary is /usr/bin/cpp.        
                                                                               
The following directories, or symbolic links to directories, must be in        
/lib, if the corresponding subsystem is installed:                             
                                                                               
modules   Loadable kernel modules (optional)                                   
                                                                               
/lib<qual> : Alternate format essential shared libraries (optional)            
                                                                               
There may be one or more variants of the /lib directory on systems which       
support more than one binary format requiring separate libraries.              
                                                                               
This is commonly used for 64-bit or 32-bit support on systems which support    
multiple binary formats, but require libraries of the same name. In this       
case, /lib32 and /lib64 might be the library directories, and /lib a symlink   
to one of them.                                                                
                                                                               
If one or more of these directories exist, the requirements for their contents 
are the same as the normal /lib directory, except that /lib<qual>/cpp is       
not required.                                                                  
                                                                               
/lib<qual>/cpp is still permitted: this allows the case where /lib and         
/lib<qual> are the same (one is a symbolic link to the other).                 
-----------------------------------------------------------------------------

1.10. /lost+found

  As was explained earlier during the overview of the FSSTND, Linux should
always go through a proper shutdown. Sometimes your system might crash or a
power failure might take the machine down. Either way, at the next boot, a
lengthy filesystem check (the speed of this check is dependent on the type of
filesystem that you actually use. ie. ext3 is faster than ext2 because it is
a journalled filesystem) using fsck will be done. Fsck will go through the
system and try to recover any corrupt files that it finds. The result of this
recovery operation will be placed in this directory. The files recovered are
not likely to be complete or make much sense but there always is a chance
that something worthwhile is recovered. Each partition has its own lost+found
directory. If you find files in there, try to move them back to their
original location. If you find something like a broken symbolic link to
'file', you have to reinstall the file/s from the corresponding RPM, since
your file system got damaged so badly that the files were mutilated beyond
recognition. Below is an example of a /lost+found directory. As you can see,
the vast majority of files contained here are in actual fact sockets. As for
the rest of the other files they were found to be damaged system files and
personal files. These files were not able to be recovered.

 
      total 368                                                              
      -rw-r--r-- 1 root root 110891 Oct 5 14:14 #388200                      
      -rw-r--r-- 1 root root 215 Oct 5 14:14 #388201                         
      -rw-r--r-- 1 root root 110303 Oct 6 23:09 #388813                      
      -rw-r--r-- 1 root root 141 Oct 6 23:09 #388814                         
      -rw-r--r-- 1 root root 110604 Oct 6 23:09 #388815a                     
      -rw-r--r-- 1 root root 194 Oct 6 23:09 #388816                         
      srwxr-xr-x 1 root root 0 Oct 6 13:00 #51430                            
      srwxr-xr-x 1 root root 0 Oct 6 00:23 #51433                            
      -rw------- 1 root root 63 Oct 6 00:23 #51434                           
      srwxr-xr-x 1 root root 0 Oct 6 13:00 #51436                            
      srwxrwxrwx 1 root root 0 Oct 6 00:23 #51437                            
      srwx------ 1 root root 0 Oct 6 00:23 #51438                            
      -rw------- 1 root root 63 Oct 6 13:00 #51439                           
      srwxrwxrwx 1 root root 0 Oct 6 13:00 #51440                            
      srwx------ 1 root root 0 Oct 6 13:00 #51442                            
      -rw------- 1 root root 63 Oct 6 23:09 #51443                           
      srwx------ 1 root root 0 Oct 6 10:40 #51445                            
      srwxrwxrwx 1 root root 0 Oct 6 23:09 #51446                            
      srwx------ 1 root root 0 Oct 6 23:09 #51448                            
                                                                             
-----------------------------------------------------------------------------

1.11. /media

 Amid much controversy and consternation on the part of system and network
administrators a directory containing mount points for removable media has
now been created. Funnily enough, it has been named /media.

 
This directory contains subdirectories which are used as mount points for       
removeable media such as floppy disks, cdroms and zip disks.                    
                                                                                
The motivation for the creation of this directory has been that historically    
there have been a number of other different places used to mount removeable     
media such as /cdrom, /mnt or /mnt/cdrom. Placing the mount points for all      
removeable media directly in the root directory would potentially result in     
a large number of extra directories in /. Although the use of subdirectories    
in /mnt as a mount point has recently been common, it conflicts with a much     
older tradition of using /mnt directly as a temporary mount point.              
                                                                                
The following directories, or symbolic links to directories, must be in /media, 
if the corresponding subsystem is installed:                                    
                                                                                
floppy     Floppy drive (optional)                                              
cdrom      CD-ROM drive (optional)                                              
cdrecorder CD writer (optional)                                                 
zip        Zip drive (optional)                                                 
                                                                                
On systems where more than one device exists for mounting a certain type of     
media, mount directories can be created by appending a digit to the name of     
those available above starting with '0', but the unqualified name must also     
exist.                                                                          
                                                                                
A compliant implementation with two CDROM drives might have /media/cdrom0       
and /media/cdrom1 with /media/cdrom a symlink to either of these.               

 Please see the section on the /mnt directory to achieve a better
understanding of the process on mounting and unmounting filesystems.
-----------------------------------------------------------------------------

1.12. /mnt

This is a generic mount point under which you mount your filesystems or
devices. Mounting is the process by which you make a filesystem available to
the system. After mounting your files will be accessible under the
mount-point. This directory usually contains mount points or sub-directories
where you mount your floppy and your CD. You can also create additional
mount-points here if you wish. Standard mount points would include /mnt/cdrom
and /mnt/floppy. There is no limitation to creating a mount-point anywhere on
your system but by convention and for sheer practicality do not litter your
file system with mount-points. It should be noted that some distributions
like Debian allocate /floppy and /cdrom as mount points while Redhat and
Mandrake puts them in /mnt/floppy and /mnt/cdrom respectively.

  However, it should be noted that as of FSSTND version 2.3 the purpose of
this directory has changed.

 
  This directory is provided so that the system administrator may temporarily    
  mount a filesystem as needed. The content of this directory is a local issue   
  and should not affect the manner in which any program is run.                  
                                                                                 
  This directory must not be used by installation programs: a suitable temporary 
  directory not in use by the system must be used instead.                       
                                                                                 
-----------------------------------------------------------------------------

1.12.1. Mounting and unmounting

Before one can use a filesystem, it has to be mounted. The operating system
then does various bookkeeping things to make sure that everything works.
Since all files in UNIX are in a single directory tree, the mount operation
will make it look like the contents of the new filesystem are the contents of
an existing subdirectory in some already mounted filesystem.

The mounts could be done as in the following example:
                                                                             
  $ mount /dev/hda2 /home                                                    
  $ mount /dev/hda3 /usr                                                     
  $                                                                          
                                                                             
The mount command takes two arguments. The first one is the device file
corresponding to the disk or partition containing the filesystem. The second
one is the directory below which it will be mounted. After these commands the
contents of the two filesystems look just like the contents of the /home and
/usr directories, respectively. One would then say that ``/dev/hda2 is
mounted on /home'', and similarly for /usr. To look at either filesystem, one
would look at the contents of the directory on which it has been mounted,
just as if it were any other directory. Note the difference between the
device file, /dev/hda2, and the mounted-on directory, /home. The device file
gives access to the raw contents of the disk, the mounted-on directory gives
access to the files on the disk. The mounted-on directory is called the mount
point.

Linux supports many filesystem types. mount tries to guess the type of the
filesystem. You can also use the -t fstype option to specify the type
directly; this is sometimes necessary, since the heuristics mount uses do not
always work. For example, to mount an MS-DOS floppy, you could use the
following command:
  $ mount -t msdos /dev/fd0 /floppy                                          
   $                                                                         
                                                                             

The mounted-on directory need not be empty, although it must exist. Any files
in it, however, will be inaccessible by name while the filesystem is mounted.
(Any files that have already been opened will still be accessible. Files that
have hard links from other directories can be accessed using those names.)
There is no harm done with this, and it can even be useful. For instance,
some people like to have /tmp and /var/tmp synonymous, and make /tmp be a
symbolic link to /var/tmp. When the system is booted, before the /var
filesystem is mounted, a /var/tmp directory residing on the root filesystem
is used instead. When /var is mounted, it will make the /var/tmp directory on
the root filesystem inaccessible. If /var/tmp didn't exist on the root
filesystem, it would be impossible to use temporary files before mounting /
var.

If you don't intend to write anything to the filesystem, use the -r switch
for mount to do a read-only mount. This will make the kernel stop any
attempts at writing to the filesystem, and will also stop the kernel from
updating file access times in the inodes. Read-only mounts are necessary for
unwritable media, e.g., CD-ROMs.

The alert reader has already noticed a slight logistical problem. How is the
first filesystem (called the root filesystem, because it contains the root
directory) mounted, since it obviously can't be mounted on another
filesystem? Well, the answer is that it is done by magic.

For more information, see the kernel source or the Kernel Hackers' Guide.

The root filesystem is magically mounted at boot time, and one can rely on it
to always be mounted. If the root filesystem can't be mounted, the system
does not boot. The name of the filesystem that is magically mounted as root
is either compiled into the kernel, or set using LILO or rdev.

The root filesystem is usually first mounted read-only. The startup scripts
will then run fsck to verify its validity, and if there are no problems, they
will re-mount it so that writes will also be allowed. fsck must not be run on
a mounted filesystem, since any changes to the filesystem while fsck is
running will cause trouble. Since the root filesystem is mounted read-only
while it is being checked, fsck can fix any problems without worry, since the
remount operation will flush any metadata that the filesystem keeps in
memory.

On many systems there are other filesystems that should also be mounted
automatically at boot time. These are specified in the /etc/fstab file; see
the fstab man page for details on the format. The details of exactly when the
extra filesystems are mounted depend on many factors, and can be configured
by each administrator if need be.

When a filesystem no longer needs to be mounted, it can be unmounted with 
umount.

It should of course be unmount, but the n mysteriously disappeared in the
70s, and hasn't been seen since. Please return it to Bell Labs, NJ, if you
find it.

umount takes one argument: either the device file or the mount point. For
example, to unmount the directories of the previous example, one could use
the commands
  $ umount /dev/hda2                                                         
  $ umount /usr                                                              
  $                                                                          
                                                                             

See the man page for further instructions on how to use the command. It is
imperative that you always unmount a mounted floppy. Don't just pop the
floppy out of the drive! Because of disk caching, the data is not necessarily
written to the floppy until you unmount it, so removing the floppy from the
drive too early might cause the contents to become garbled. If you only read
from the floppy, this is not very likely, but if you write, even
accidentally, the result may be catastrophic.

Mounting and unmounting requires super user privileges, i.e., only root can
do it. The reason for this is that if any user can mount a floppy on any
directory, then it is rather easy to create a floppy with, say, a Trojan
horse disguised as /bin/sh, or any other often used program. However, it is
often necessary to allow users to use floppies, and there are several ways to
do this:

  * Give the users the root password. This is obviously bad security, but is
    the easiest solution. It works well if there is no need for security
    anyway, which is the case on many non-networked, personal systems.
   
  * Use a program such as sudo to allow users to use mount. This is still bad
    security, but doesn't directly give super user privileges to everyone. 
    [1]
   
  * Make the users use mtools, a package for manipulating MS-DOS filesystems,
    without mounting them. This works well if MS-DOS floppies are all that is
    needed, but is rather awkward otherwise.
   
  * List the floppy devices and their allowable mount points together with
    the suitable options in /etc/fstab.
   

The last alternative can be implemented by adding a line like the following
to the /etc/fstab file:

  /dev/fd0 /floppy                                                           
  msdos user,noauto 0 0                                                      
                                                                             

The columns are: device file to mount, directory to mount on, filesystem
type, options, backup frequency (used by dump), and fsck pass number (to
specify the order in which filesystems should be checked upon boot; 0 means
no check).

The noauto option stops this mount to be done automatically when the system
is started (i.e., it stops mount -a from mounting it). The user option allows
any user to mount the filesystem, and, because of security reasons, disallows
execution of programs (normal or setuid) and interpretation of device files
from the mounted filesystem. After this, any user can mount a floppy with an
msdos filesystem with the following command:

 
                                                                             
  $ mount /floppy                                                            
  $                                                                          
                                                                             

The floppy can (and needs to, of course) be unmounted with the corresponding 
umount command.

If you want to provide access to several types of floppies, you need to give
several mount points. The settings can be different for each mount point. For
example, to give access to both MS-DOS and ext2 floppies, you could have the
following to lines in /etc/fstab:

  /dev/fd0 /dosfloppy msdos user,noauto 0 0 /dev/fd0                         
  /ext2floppy ext2 user,noauto 0 0                                           
                                                                             

For MS-DOS filesystems (not just floppies), you probably want to restrict
access to it by using the uid, gid, and umask filesystem options, described
in detail on the mount manual page. If you aren't careful, mounting an MS-DOS
filesystem gives everyone at least read access to the files in it, which is
not a good idea.
-----------------------------------------------------------------------------

1.13. /opt

  This directory is reserved for all the software and add-on packages that
are not part of the default installation. For example, StarOffice, Kylix,
Netscape Communicator and WordPerfect packages are normally found here. To
comply with the FSSTND, all third party applications should be installed in
this directory. Any package to be installed here must locate its static files
(ie. extra fonts, clipart, database files) must locate its static files in a
separate /opt/'package' or /opt/'provider' directory tree (similar to the way
in which Windows will install new software to its own directory tree C:\
Windows\Progam Files\"Program Name"), where 'package' is a name that
describes the software package and 'provider' is the provider's LANANA
registered name.

  Although most distributions neglect to create the directories /opt/bin, /
opt/doc, /opt/include, /opt/info, /opt/lib, and /opt/man they are reserved
for local system administrator use. Packages may provide "front-end" files
intended to be placed in (by linking or copying) these reserved directories
by the system administrator, but must function normally in the absence of
these reserved directories. Programs to be invoked by users are located in
the directory /opt/'package'/bin. If the package includes UNIX manual pages,
they are located in /opt/'package'/man and the same substructure as /usr/
share/man must be used. Package files that are variable must be installed in
/var/opt. Host-specific configuration files are installed in /etc/opt.

  Under no circumstances are other package files to exist outside the /opt, /
var/opt, and /etc/opt hierarchies except for those package files that must
reside in specific locations within the filesystem tree in order to function
properly. For example, device lock files in /var/lock and devices in /dev.
Distributions may install software in /opt, but must not modify or delete
software installed by the local system administrator without the assent of
the local system administrator.

  The use of /opt for add-on software is a well-established practice in the
UNIX community. The System V Application Binary Interface [AT&T 1990], based
on the System V Interface Definition (Third Edition) and the Intel Binary
Compatibility Standard v. 2 (iBCS2) provides for an /opt structure very
similar to the one defined here.

  Generally, all data required to support a package on a system must be
present within /opt/'package', including files intended to be copied into /
etc/opt/'package' and /var/opt/'package' as well as reserved directories in /
opt. The minor restrictions on distributions using /opt are necessary because
conflicts are possible between distribution installed and locally installed
software, especially in the case of fixed pathnames found in some binary
software.

  The structure of the directories below /opt/'provider' is left up to the
packager of the software, though it is recommended that packages are
installed in /opt/'provider'/'package' and follow a similar structure to the
guidelines for /opt/package. A valid reason for diverging from this structure
is for support packages which may have files installed in /opt/ 'provider'/
lib or /opt/'provider'/bin.
-----------------------------------------------------------------------------

1.14. /proc

/proc is very special in that it is also a virtual filesystem. It's sometimes
referred to as a process information pseudo-file system. It doesn't contain
'real' files but runtime system information (e.g. system memory, devices
mounted, hardware configuration, etc). For this reason it can be regarded as
a control and information centre for the kernel. In fact, quite a lot of
system utilities are simply calls to files in this directory. For example,
'lsmod' is the same as 'cat /proc/modules' while 'lspci' is a synonym for
'cat /proc/pci'. By altering files located in this directory you can even
read/change kernel parameters (sysctl) while the system is running.

The most distinctive thing about files in this directory is the fact that all
of them have a file size of 0, with the exception of kcore, mtrr and self. A
directory listing looks similar to the following:

total 525256                                                                 
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 1                    
dr-xr-xr-x    3 daemon   root            0 Jan 19 15:00 109                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 170                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 173                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 178                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 2                    
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 3                    
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 4                    
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 421                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 425                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 433                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 439                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 444                  
dr-xr-xr-x    3 daemon   daemon          0 Jan 19 15:00 446                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 449                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 453                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 456                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 458                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 462                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 463                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 464                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 465                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 466                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 467                  
dr-xr-xr-x    3 gdm      gdm             0 Jan 19 15:00 472                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 483                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 5                    
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 6                    
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 7                    
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 8                    
-r--r--r--    1 root     root            0 Jan 19 15:00 apm                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 bus                  
-r--r--r--    1 root     root            0 Jan 19 15:00 cmdline              
-r--r--r--    1 root     root            0 Jan 19 15:00 cpuinfo              
-r--r--r--    1 root     root            0 Jan 19 15:00 devices              
-r--r--r--    1 root     root            0 Jan 19 15:00 dma                  
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 driver               
-r--r--r--    1 root     root            0 Jan 19 15:00 execdomains          
-r--r--r--    1 root     root            0 Jan 19 15:00 fb                   
-r--r--r--    1 root     root            0 Jan 19 15:00 filesystems          
dr-xr-xr-x    2 root     root            0 Jan 19 15:00 fs                   
dr-xr-xr-x    4 root     root            0 Jan 19 15:00 ide                  
-r--r--r--    1 root     root            0 Jan 19 15:00 interrupts           
-r--r--r--    1 root     root            0 Jan 19 15:00 iomem                
-r--r--r--    1 root     root            0 Jan 19 15:00 ioports              
dr-xr-xr-x   18 root     root            0 Jan 19 15:00 irq                  
-r--------    1 root     root     536809472 Jan 19 15:00 kcore               
-r--------    1 root     root            0 Jan 19 14:58 kmsg                 
-r--r--r--    1 root     root            0 Jan 19 15:00 ksyms                
-r--r--r--    1 root     root            0 Jan 19 15:00 loadavg              
-r--r--r--    1 root     root            0 Jan 19 15:00 locks                
-r--r--r--    1 root     root            0 Jan 19 15:00 mdstat               
-r--r--r--    1 root     root            0 Jan 19 15:00 meminfo              
-r--r--r--    1 root     root            0 Jan 19 15:00 misc                 
-r--r--r--    1 root     root            0 Jan 19 15:00 modules              
-r--r--r--    1 root     root            0 Jan 19 15:00 mounts               
-rw-r--r--    1 root     root          137 Jan 19 14:59 mtrr                 
dr-xr-xr-x    3 root     root            0 Jan 19 15:00 net                  
dr-xr-xr-x    2 root     root            0 Jan 19 15:00 nv                   
-r--r--r--    1 root     root            0 Jan 19 15:00 partitions           
-r--r--r--    1 root     root            0 Jan 19 15:00 pci                  
dr-xr-xr-x    4 root     root            0 Jan 19 15:00 scsi                 
lrwxrwxrwx    1 root     root           64 Jan 19 14:58 self -> 483          
-rw-r--r--    1 root     root            0 Jan 19 15:00 slabinfo             
-r--r--r--    1 root     root            0 Jan 19 15:00 stat                 
-r--r--r--    1 root     root            0 Jan 19 15:00 swaps                
dr-xr-xr-x   10 root     root            0 Jan 19 15:00 sys                  
dr-xr-xr-x    2 root     root            0 Jan 19 15:00 sysvipc              
dr-xr-xr-x    4 root     root            0 Jan 19 15:00 tty                  
-r--r--r--    1 root     root            0 Jan 19 15:00 uptime               
-r--r--r--    1 root     root            0 Jan 19 15:00 version              

Each of the numbered directories corresponds to an actual process ID. Looking
at the process table, you can match processes with the associated process ID.
For example, the process table might indicate the following for the secure
shell server:

# ps ax | grep sshd                                                          
439 ? S 0:00 /usr/sbin/sshd                                                  

Details of this process can be obtained by looking at the associated files in
the directory for this process, /proc/460. You might wonder how you can see
details of a process that has a file size of 0. It makes more sense if you
think of it as a window into the kernel. The file doesn't actually contain
any data; it just acts as a pointer to where the actual process information
resides. For example, a listing of the files in the /proc/460 directory looks
similar to the following:

total 0                                                                       
-r--r--r--    1 root     root            0 Jan 19 15:02 cmdline               
lrwxrwxrwx    1 root     root            0 Jan 19 15:02 cwd -> /              
-r--------    1 root     root            0 Jan 19 15:02 environ               
lrwxrwxrwx    1 root     root            0 Jan 19 15:02 exe -> /usr/sbin/sshd 
dr-x------    2 root     root            0 Jan 19 15:02 fd                    
-r--r--r--    1 root     root            0 Jan 19 15:02 maps                  
-rw-------    1 root     root            0 Jan 19 15:02 mem                   
lrwxrwxrwx    1 root     root            0 Jan 19 15:02 root -> /             
-r--r--r--    1 root     root            0 Jan 19 15:02 stat                  
-r--r--r--    1 root     root            0 Jan 19 15:02 statm                 
-r--r--r--    1 root     root            0 Jan 19 15:02 status                

The purpose and contents of each of these files is explained below:

/proc/PID/cmdline
    Command line arguments.
   
/proc/PID/cpu
    Current and last cpu in which it was executed.
   
/proc/PID/cwd
    Link to the current working directory.
   
/proc/PID/environ
    Values of environment variables.
   
/proc/PID/exe
    Link to the executable of this process.
   
/proc/PID/fd
    Directory, which contains all file descriptors.
   
/proc/PID/maps
    Memory maps to executables and library files.
   
/proc/PID/mem
    Memory held by this process.
   
/proc/PID/root
    Link to the root directory of this process.
   
/proc/PID/stat
    Process status.
   
/proc/PID/statm
    Process memory status information.
   
/proc/PID/status
    Process status in human readable form.
   

Should you wish to know more, the man page for proc describes each of the
files associated with a running process ID in far greater detail.

Even though files appear to be of size 0, examining their contents reveals
otherwise:

# cat status                                                                 

Name: sshd                                                                   
State: S (sleeping)                                                          
Tgid: 439                                                                    
Pid: 439                                                                     
PPid: 1                                                                      
TracerPid: 0                                                                 
Uid: 0 0 0 0                                                                 
Gid: 0 0 0 0                                                                 
FDSize: 32                                                                   
Groups:                                                                      
VmSize:     2788 kB                                                          
VmLck:        0 kB                                                           
VmRSS:     1280 kB                                                           
VmData:      252 kB                                                          
VmStk:       16 kB                                                           
VmExe:      268 kB                                                           
VmLib:     2132 kB                                                           
SigPnd: 0000000000000000                                                     
SigBlk: 0000000000000000                                                     
SigIgn: 8000000000001000                                                     
SigCgt: 0000000000014005                                                     
CapInh: 0000000000000000                                                     
CapPrm: 00000000fffffeff                                                     
CapEff: 00000000fffffeff                                                     

The files in the /proc directory act very similar to the process ID
subdirectory files. For example, examining the contents of the /proc/
interrupts file displays something like the following:

# cat interrupts                                                             

           CPU0                                                              
  0:      32657          XT-PIC  timer                                       
  1:       1063          XT-PIC  keyboard                                    
  2:          0          XT-PIC  cascade                                     
  8:          3          XT-PIC  rtc                                         
  9:          0          XT-PIC  cmpci                                       
 11:        332          XT-PIC  nvidia                                      
 14:       5289          XT-PIC  ide0                                        
 15:         13          XT-PIC  ide1                                        
NMI:          0                                                              
ERR:          0                                                              

Each of the numbers down the left-hand column represents the interrupt that
is in use. Examining the contents of the file dynamically gathers the
associated data and displays it to the screen. Most of the /proc file system
is read-only; however, some files allow kernel variable to be changed. This
provides a mechanism to actually tune the kernel without recompiling and
rebooting.

The procinfo utility summarizes /proc file system information into a display
similar to the following:

# /usr/bin/procinfo                                                          

Linux 2.4.18 (root@DEB) (gcc 2.95.4 20011002 ) #2 1CPU [DEB.(none)]             
                                                                                
Memory:      Total        Used        Free      Shared     Buffers      Cached  
Mem:        513908      107404      406504           0        2832       82180  
Swap:       265032           0      265032                                      
                                                                                
Bootup: Sun Jan 19 14:58:27 2003    Load average: 0.29 0.13 0.05 1/30 566       
                                                                                
user  :       0:00:10.26   2.3%  page in :    74545  disk 1:     6459r     796w 
nice  :       0:00:00.00   0.0%  page out:     9416  disk 2:       19r       0w 
system:       0:00:19.55   4.5%  swap in :        1                             
idle  :       0:06:48.30  93.2%  swap out:        0                             
uptime:       0:07:18.11         context :    22059                             
                                                                                
irq  0:     43811 timer                 irq  9:         0 cmpci                 
irq  1:      1427 keyboard              irq 11:       332 nvidia                
irq  2:         0 cascade [4]           irq 12:         2                       
irq  6:         2                       irq 14:      7251 ide0                  
irq  8:         3 rtc                   irq 15:        83 ide1                  

/proc/apm
      Advanced power management info.
   
/proc/bus
    Directory containing bus specific information.
   
/proc/cmdline
    Kernel command line.
   
/proc/cpuinfo
      Information about the processor, such as its type, make, model, and
    performance.
   
/proc/devices
      List of device drivers configured into the currently running kernel
    (block and character).
   
/proc/dma
    Shows which DMA channels are being used at the moment.
   
/proc/driver
    Various drivers grouped here, currently rtc
   
/proc/execdomains
    Execdomains, related to security.
   
/proc/fb
    Frame Buffer devices.
   
/proc/filesystems
    Filesystems configured/supported into/by the kernel.
   
/proc/fs
    File system parameters, currently nfs/exports.
   
/proc/ide
    This subdirectory contains information about all IDE devices of which the
    kernel is aware. There is one subdirectory for each IDE controller, the
    file drivers and a link for each IDE device, pointing to the device
    directory in the controller-specific subtree. The file drivers contains
    general information about the drivers used for the IDE devices. More
    detailed information can be found in the controller-specific
    subdirectories. These are named ide0, ide1 and so on. Each of these
    directories contains the files shown here:
   
    /proc/ide/ide?/channel
        IDE channel (0 or 1)
       
    /proc/ide/ide?/config
          Configuration (only for PCI/IDE bridge)
       
    /proc/ide/ide?/mate
        Mate name (onchip partnered controller)
       
    /proc/ide/ide?/model
        Type/Chipset of IDE controller
       
   
          Each device connected to a controller has a separate subdirectory
        in the controllers directory. The following files listed are
        contained in these directories:
       
    /proc/ide/ide?/model/cache
        The cache.
       
    /proc/ide/ide?/model/capacity
          Capacity of the medium (in 512Byte blocks)
       
    /proc/ide/ide?/model/driver
          driver and version
       
    /proc/ide/ide?/model/geometry
          physical and logical geometry
       
    /proc/ide/ide?/model/identify
          device identify block
       
    /proc/ide/ide?/model/media
        media type
       
    /proc/ide/ide?/model/model
          device identifier
       
    /proc/ide/ide?/model/settings
          device setup
       
    /proc/ide/ide?/model/smart_thresholds
          IDE disk management thresholds
       
    /proc/ide/ide?/model/smart_values
          IDE disk management values
       
   
   
/proc/interrupts
    Shows which interrupts are in use, and how many of each there have been.
   
   
        You can, for example, check which interrupts are currently in use and
        what they are used for by looking in the file /proc/interrupts:
       
   
        # cat /proc/interrupts                                               
       
   
                                                                             
          CPU0 0: 8728810                                                    
          XT-PIC timer 1: 895                                                
          XT-PIC keyboard 2:                                                 
          0 XT-PIC cascade 3: 531695                                         
          XT-PIC aha152x 4: 2014133                                          
          XT-PIC serial 5: 44401                                             
          XT-PIC pcnet_cs 8: 2                                               
          XT-PIC rtc 11: 8                                                   
          XT-PIC i82365 12: 182918                                           
          XT-PIC PS/2 Mouse 13: 1                                            
          XT-PIC fpu 14: 1232265                                             
          XT-PIC ide0 15: 7                                                  
          XT-PIC ide1 NMI: 0                                                 
                                                                             
       
   
        In 2.4 based kernels a couple of lines were added to this file LOC &
        ERR (this is the output of an SMP machine):
       
   
        # cat /proc/interrupts                                               
       
   
         
                                                                             
          CPU0 CPU1                                                          
          0: 1243498 1214548 IO-APIC-edge timer                              
          1: 8949 8958 IO-APIC-edge keyboard                                 
          2: 0 0 XT-PIC cascade                                              
          5: 11286 10161 IO-APIC-edge soundblaster                           
          8: 1 0 IO-APIC-edge rtc                                            
          9: 27422 27407 IO-APIC-edge 3c503                                  
          12: 113645 113873 IO-APIC-edge PS/2 Mouse                          
          13: 0 0 XT-PIC fpu 14: 22491 24012 IO-APIC-edge ide0               
          15: 2183 2415 IO-APIC-edge ide1                                    
          17: 30564 30414 IO-APIC-level eth0                                 
          18: 177 164 IO-APIC-level bttv NMI: 2457961 2457959                
                      LOC: 2457882 2457881 ERR: 2155                         
                                                                             
       
   
        NMI is incremented in this case because every timer interrupt
        generates a NMI (Non Maskable Interrupt) which is used by the NMI
        Watchdog to detect lookups.
       
   
        LOC is the local interrupt counter of the internal APIC of every CPU.
       
   
        ERR is incremented in the case of errors in the IO-APIC bus (the bus
        that connects the CPUs in an SMP system. This means that an error has
        been detected, the IO-APIC automatically retries the transmission, so
        it should not be a big problem, but you should read the SMP-FAQ.
       
   
        In this context it could be interesting to note the new irq directory
        in 2.4. It could be used to set IRQ to CPU affinity, this means that
        you can "hook" an IRQ to only one CPU, or to exclude a CPU from
        handling IRQs. The contents of the irq subdir is one subdir for each
        IRQ, and one file; prof_cpu_mask. For example,
       
   
                                                                             
          # ls /proc/irq/ 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask             
                          1 11 13 15 17 19 3 5 7 9                           
                                                                             
       
   
                                                                             
          # ls /proc/irq/0/ smp_affinity                                     
                                                                             
       
   
        The contents of the prof_cpu_mask file and each smp_affinity file for
        each IRQ is the same by default:
       
   
         
          # cat /proc/irq/0/smp_affinity                                     
          ffffffff                                                           
                                                                             
       
   
        It's a bitmask, in which you can specify which CPUs can handle the
        IRQ, you can set it by doing:
       
   
        # echo 1 > /proc/irq/prof_cpu_mask                                   
       
   
        This means that only the first CPU will handle the IRQ, but you can
        also echo 5 which means that only the first and fourth CPU can handle
        the IRQ. The way IRQs are routed is handled by the IO-APIC, and its
        Round Robin between all the CPUs which are allowed to handle it. As
        usual the kernel has more info than you and does a better job than
        you, so the defaults are the best choice for almost everyone.
       
   
   
/proc/iomem
    Memory map.
   
/proc/ioports
    Which I/O ports are in use at the moment.
   
/proc/irq
    Masks for irq to cpu affinity.
   
/proc/isapnp
      ISA PnP (Plug&Play) Info.
   
/proc/kcore
    An image of the physical memory of the system (can be ELF or A.OUT
    (deprecated in 2.4)). This is exactly the same size as your physical
    memory, but does not really take up that much memory; it is generated on
    the fly as programs access it. (Remember: unless you copy it elsewhere,
    nothing under /proc takes up any disk space at all.)
   
/proc/kmsg
    Messages output by the kernel. These are also routed to syslog.
   
/proc/ksyms
    Kernel symbol table.
   
/proc/loadavg
    The 'load average' of the system; three indicators of how much work the
    system has done during the last 1, 5 & 15 minutes.
   
/proc/locks
    Kernel locks.
   
/proc/meminfo
    Information about memory usage, both physical and swap. Concatenating
    this file produces similar results to using 'free' or the first few lines
    of 'top'.
   
/proc/misc
    Miscellaneous pieces of information. This is for information that has no
    real place within the rest of the proc filesystem.
   
/proc/modules
    Kernel modules currently loaded. Typically its output is the same as that
    given by the 'lsmod' command.
   
/proc/mounts
    Mounted filesystems
   
/proc/mtrr
    Information regarding mtrrs. (On Intel P6 family processors (Pentium Pro,
    Pentium II and later) the Memory Type Range Registers (MTRRs) may be used
    to control processor access to memory ranges. This is most useful when
    you have a video (VGA) card on a PCI or AGP bus. Enabling write-combining
    allows bus write transfers to be combined into a larger transfer before
    bursting over the PCI/AGP bus. This can increase performance of image
    write operations 2.5 times or more. The Cyrix 6x86, 6x86MX and M II
    processors have Address Range Registers (ARRs) which provide a similar
    functionality to MTRRs. For these, the ARRs are used to emulate the
    MTRRs. The AMD K6-2 (stepping 8 and above) and K6-3 processors have two
    MTRRs. These are supported. The AMD Athlon family provide 8 Intel style
    MTRRs. The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining.
    These are also supported. The VIA Cyrix III and VIA C3 CPUs offer 8 Intel
    style MTRRs.) For more details regarding mtrr technology see /usr/src/
    linux/Documentation/mtrr.txt.
   
/proc/net
    Status information about network protocols.
   
IPv6 information
     
   
    /proc/net/udp6
          UDP sockets (IPv6).
       
    /proc/net/tcp6
        TCP sockets (IPv6).
       
    /proc/net/raw6
          Raw device statistics (IPv6).
       
    /proc/net/igmp6
        IP multicast addresses, which this host joined (IPv6).
       
    /proc/net/if_inet6
        List of IPv6 interface addresses.
       
    /proc/net/ipv6_route
        Kernel routing table for IPv6.
       
    /proc/net/rt6_stats
        Global IPv6 routing tables statistics.
       
    /proc/net/sockstat6
        Socket statistics (IPv6).
       
    /proc/net/snmp6
        Snmp data (IPv6).
       
   
   
General Network information
     
   
    /proc/net/arp
          Kernel ARP table.
       
    /proc/net/dev
        network devices with statistics.
       
    /proc/net/dev_mcast
        the Layer2 multicast groups which a device is listening to (interface
        index, label, number of references, number of bound addresses).
       
    /proc/net/dev_stat
        network device status.
       
    /proc/net/ip_fwchains
          Firewall chain linkage.
       
    /proc/net/ip_fwnames
        Firewall chain names.
       
    /proc/net/ip_masq
          Directory containing the masquerading tables.
       
    /proc/net/ip_masquerade
        Major masquerading table.
       
    /proc/net/netstat
        Network statistics.
       
    /proc/net/raw
          raw device statistics.
       
    /proc/net/route
        Kernel routing table.
       
    /proc/net/rpc
          Directory containing rpc info.
       
    /proc/net/rt_cache
        Routing cache.
       
    /proc/net/snmp
        SNMP data.
       
    /proc/net/sockstat
        Socket statistics.
       
    /proc/net/tcp
          TCP sockets.
       
    /proc/net/tr_rif
          Token ring RIF routing table.
       
    /proc/net/udp
        UDP sockets.
       
    /proc/net/unix
        UNIX domain sockets.
       
    /proc/net/wireless
          Wireless interface data (Wavelan etc).
       
    /proc/net/igmp
        IP multicast addresses, which this host joined.
       
    /proc/net/psched
        Global packet scheduler parameters.
       
    /proc/net/netlink
        List of PF_NETLINK sockets.
       
    /proc/net/ip_mr_vifs
        List of multicast virtual interfaces.
       
    /proc/net/ip_mr_cache
        List of multicast routing cache.
       
        You can use this information to see which network devices are
        available in your system and how much traffic was routed over those
        devices. In addition, each Channel Bond interface has its own
        directory. For example, the bond0 device will have a directory called
        /proc/net/bond0/. It will contain information that is specific to
        that bond, such as the current slaves of the bond, the link status of
        the slaves, and how many times the slaves link has failed.
       
   
   
/proc/parport
      The directory /proc/parport contains information about the parallel
    ports of your system. It has one subdirectory for each port, named after
    the port number (0,1,2,...).
   
    /proc/parport/autoprobe
          Any IEEE-1284 device ID information that has been acquired.
       
    /proc/parport/devices
        list of the device drivers using that port. A + will appear by the
        name of the device currently using the port (it might not appear
        against any).
       
    /proc/parport/hardware
        Parallel port's base address, IRQ line and DMA channel.
       
    /proc/parport/irq
        IRQ that parport is using for that port. This is in a separate file
        to allow you to alter it by writing a new value in (IRQ number or
        none).
       
   
   
/proc/partitions
    Table of partitions known to the system
   
/proc/pci, /proc/bus/pci
      Depreciated info of PCI bus.
   
/proc/rtc
    Real time clock
   
/proc/scsi
    If you have a SCSI host adapter in your system, you'll find a
    subdirectory named after the driver for this adapter in /proc/scsi.
    You'll also see a list of all recognized SCSI devices in /proc/scsi. The
    directory named after the driver has one file for each adapter found in
    the system. These files contain information about the controller,
    including the used IRQ and the IO address range. The amount of
    information shown is dependent on the adapter you use.
   
/proc/self
    A symbolic link to the process directory of the program that is looking
    at /proc. When two processes look at /proc, they get different links.
    This is mainly a convenience to make it easier for programs to get at
    their process directory.
   
/proc/slabinfo
      The slabinfo file gives information about memory usage at the slab
    level. Linux uses slab pools for memory management above page level in
    version 2.2. Commonly used objects have their own slab pool (such as
    network buffers, directory cache, and so on).
   
/proc/stat
    Overall/various statistics about the system, such as the number of page
    faults since the system was booted.
   
/proc/swaps
    Swap space utilization
   
/proc/sys
      This is not only a source of information, it also allows you to change
    parameters within the kernel without the need for recompilation or even a
    system reboot. Take care when attempting this as it can both optimize
    your system and also crash it. It is advisable to read both documentation
    and source before actually making adjustments. The entries in /proc may
    change slightly between kernel versions, so if there is any doubt review
    the kernel documentation in the directory /usr/src/linux/Documentation.
    Under some circumstances, you may have no alternative but to reboot the
    machine once an error occurs. To change a value, simply echo the new
    value into the file. An example is given below in the section on the file
    system data. Of course, you need to be 'root' to do any of this. You can
    create your own boot script to perform this every time your system boots.
   
/proc/sys/fs
    Contains file system data. This subdirectory contains specific file
    system, file handle, inode, dentry and quota information.
   
    dentry-state
        Status of the directory cache. Since directory entries are
        dynamically allocated and deallocated, this file indicates the
        current status. It holds six values, in which the last two are not
        used and are always zero. The others are listed below:
       
   
                                                                             
          File      Content                                                  
          nr_dentry Almost always zero                                       
          nr_unused Number of unused cache entries                           
          age_limit in seconds after the entry may be                        
                    reclaimed, when memory is short want_pages internally    
                                                                             
       
    dquot-max
          The file dquot-max shows the maximum number of cached disk quota
        entries.
       
    dquot-nr
          shows the number of allocated disk quota entries and the number of
        free disk quota entries. If the number of available cached disk
        quotas is very low and you have a large number of simultaneous system
        users, you might want to raise the limit.
       
    file-nr and file-max
        The kernel allocates file handles dynamically, but doesn't free them
        again at this time. The value in file-max denotes the maximum number
        of file handles that the Linux kernel will allocate. When you get a
        lot of error messages about running out of file handles, you might
        want to raise this limit. The default value is 4096. To change it,
        just write the new number into the file:
       
   
          # cat /proc/sys/fs/file-max                                        
          4096                                                               
          # echo 8192 > /proc/sys/fs/file-max                                
          # cat /proc/sys/fs/file-max                                        
          8192                                                               
                                                                             
       
   
        This method of revision is useful for all customizable parameters of
        the kernel - simply echo the new value to the corresponding file.
       
   
        The three values in file-nr denote the number of allocated file
        handles, the number of used file handles, and the maximum number of
        file handles. When the allocated file handles come close to the
        maximum, but the number of actually used handles is far behind,
        you've encountered a peak in your usage of file handles and you don't
        need to increase the maximum.
       
    inode-state, inode-nr and inode-max
        As with file handles, the kernel allocates the inode structures
        dynamically, but can't free them yet.
       
   
        The value in inode-max denotes the maximum number of inode handlers.
        This value should be 3 to 4 times larger than the value in file-max,
        since stdin, stdout, and network sockets also need an inode struct to
        handle them. If you regularly run out of inodes, you should increase
        this value.
       
   
        The file inode-nr contains the first two items from inode-state, so
        we'll skip to that file...
       
   
        inode-state contains three actual numbers and four dummy values. The
        numbers are nr_inodes, nr_free_inodes, and preshrink (in order of
        appearance).
       
    nr_inodes
        Denotes the number of inodes the system has allocated. This can be
        slightly more than inode-max because Linux allocates them one pageful
        at a time.
       
    nr_free_inodes
        Represents the number of free inodes and preshrink is nonzero when
        nr_inodes is greater than inode-max and the system needs to prune the
        inode list instead of allocating more.
       
    super-nr and super-max
          Again, super block structures are allocated by the kernel, but not
        freed. The file super-max contains the maximum number of super block
        handlers, where super-nr shows the number of currently allocated
        ones. Every mounted file system needs a super block, so if you plan
        to mount lots of file systems, you may want to increase these
        numbers.
       
    binfmt_misc
          This handles the kernel support for miscellaneous binary formats.
        binfmt_misc provides the ability to register additional binary
        formats to the kernel without compiling an additional module/kernel.
        Therefore, binfmt_misc needs to know magic numbers at the beginning
        or the filename extension of the binary. It works by maintaining a
        linked list of structs that contain a description of a binary format,
        including a magic with size (or the filename extension), offset and
        mask, and the interpreter name. On request it invokes the given
        interpreter with the original program as argument, as binfmt_java and
        binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any
        default binary-formats, you have to register an additional
        binary-format. There are two general files in binfmt_misc and one
        file per registered format. The two general files are register and
        status. To register a new binary format you have to issue the command
        echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/
        binfmt_misc/register with appropriate name (the name for the /
        proc-dir entry), offset (defaults to 0, if omitted), magic, mask
        (which can be omitted, defaults to all 0xff) and last but not least,
        the interpreter that is to be invoked (for example and testing /bin/
        echo). Type can be M for usual magic matching or E for filename
        extension matching (give extension in place of magic). If you do a
        cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
        current status (enabled/disabled) of binfmt_misc. Change the status
        by echoing 0 (disables) or 1 (enables) or -1 (caution: this clears
        all previously registered binary formats) to status. For example echo
        0 > status to disable binfmt_misc (temporarily). Each registered
        handler has an entry in /proc/sys/fs/binfmt_misc. These files perform
        the same function as status, but their scope is limited to the actual
        binary format. By 'cating' this file, you also receive all related
        information about the interpreter/magic of the binfmt. An example of
        the usage of binfmt_misc (emulate binfmt_java) follows:
       
   
          cd /proc/sys/fs/binfmt_misc                                         
          echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:'  
          > register                                                          
          echo ':HTML:E::html::/usr/local/java/bin/appletviewer:'             
          > register                                                          
          echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' >   
          register                                                            
          echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' < register               
                                                                              
       
   
          These four lines add support for Java executables and Java applets
        (like binfmt_java, additionally recognizing the .html extension with
        no need to put <!--applet> to every applet file). You have to install
        the JDK and the shell-script /usr/local/java/bin/javawrapper too. It
        works around the brokenness of the Java filename handling. To add a
        Java binary, just create a link to the class-file somewhere in the
        path.
       
   
   
/proc/sys/kernel
    This directory reflects general kernel behaviors and the contents will be
    dependent upon your configuration. Here you'll find the most important
    files, along with descriptions of what they mean and how to use them.
   
    /proc/sys/kernel/acct
        The file contains three values; highwater, lowwater, and frequency.
        It exists only when BSD-style process accounting is enabled. These
        values control its behavior. If the free space on the file system
        where the log lives goes below lowwater percentage, accounting
        suspends. If it goes above highwater percentage, accounting resumes.
        Frequency determines how often you check the amount of free space
        (value is in seconds). Default settings are: 4, 2, and 30. That is,
        suspend accounting if there is less than 2 percent free; resume it if
        we have a value of 3 or more percent; consider information about the
        amount of free space valid for 30 seconds
       
    /proc/sys/kernel/ctrl-alt-del
          When the value in this file is 0, ctrl-alt-del is trapped and sent
        to the init program to handle a graceful restart. However, when the
        value is greater that zero, Linux's reaction to this key combination
        will be an immediate reboot, without syncing its dirty buffers. It
        should be noted that when a program (like dosemu) has the keyboard in
        raw mode, the ctrl-alt-del is intercepted by the program before it
        ever reaches the kernel tty layer, and it is up to the program to
        decide what to do with it.
       
    /proc/sys/kernel/domainname, /proc/sys/kernel/hostname
          These files can be controlled to set the NIS domainname and
        hostname of your box. For the classic darkstar.frop.org a simple: #
        echo "darkstar" > /proc/sys/kernel/hostname # echo "frop.org" > /proc
        /sys/kernel/domainname would suffice to set your hostname and NIS
        domainname. /proc/sys/kernel/osrelease, /proc/sys/kernel/ostype, /
        proc/sys/kernel/version The names make it pretty obvious what these
        fields contain: # cat /proc/sys/kernel/osrelease 2.2.12 # cat /proc/
        sys/kernel/ostype Linux # cat /proc/sys/kernel/version #4 Fri Oct 1
        12:41:14 PDT 1999 The files osrelease and ostype should be clear
        enough. Version needs a little more clarification. The #4 means that
        this is the 4th kernel built from this source base and the date after
        it indicates the time the kernel was built. The only way to tune
        these values is to rebuild the kernel.
       
    /proc/sys/kernel/panic
          The value in this file represents the number of seconds the kernel
        waits before rebooting on a panic. When you use the software
        watchdog, the recommended setting is 60. If set to 0, the auto reboot
        after a kernel panic is disabled, which is the default setting.
       
    /proc/sys/kernel/printk
        The four values in printk denote * console_loglevel, *
        default_message_loglevel, * minimum_console_level and *
        default_console_loglevel respectively. These values influence printk
        () behavior when printing or logging error messages, which come from
        inside the kernel. See syslog(2) for more information on the
        different log levels.
       
    /proc/sys/kernel/console_loglevel
          Messages with a higher priority than this will be printed to the
        console.
       
    /proc/sys/kernel/default_message_level
          Messages without an explicit priority will be printed with this
        priority.
       
    /proc/sys/kernel/minimum_console_loglevel
          Minimum (highest) value to which the console_loglevel can be set.
       
    /proc/sys/kernel/default_console_loglevel
          Default value for console_loglevel.
       
    /proc/sys/kernel/sg-big-buff
        This file shows the size of the generic SCSI (sg) buffer. At this
        point, you can't tune it yet, but you can change it at compile time
        by editing include/scsi/sg.h and changing the value of SG_BIG_BUFF.
        If you use a scanner with SANE (Scanner Access Now Easy) you might
        want to set this to a higher value. Refer to the SANE documentation
        on this issue.
       
    /proc/sys/kernel/modprobe
        The location where the modprobe binary is located. The kernel uses
        this program to load modules on demand.
       
   
   
/proc/sys/vm
    The files in this directory can be used to tune the operation of the
    virtual memory (VM) subsystem of the Linux kernel. In addition, one of
    the files (bdflush) has some influence on disk usage.
   
nfract
    This parameter governs the maximum number of dirty buffers in the buffer
    cache. Dirty means that the contents of the buffer still have to be
    written to disk (as opposed to a clean buffer, which can just be
    forgotten about). Setting this to a higher value means that Linux can
    delay disk writes for a long time, but it also means that it will have to
    do a lot of I/O at once when memory becomes short. A lower value will
    spread out disk I/O more evenly.
   
ndirty
      Ndirty gives the maximum number of dirty buffers that bdflush can write
    to the disk at one time. A high value will mean delayed, bursty I/O,
    while a small value can lead to memory shortage when bdflush isn't woken
    up often enough.
   
nrefill
    This is the number of buffers that bdflush will add to the list of free
    buffers when refill_freelist() is called. It is necessary to allocate
    free buffers beforehand, since the buffers are often different sizes than
    the memory pages and some bookkeeping needs to be done beforehand. The
    higher the number, the more memory will be wasted and the less often
    refill_freelist() will need to run.
   
nref_dirt
    When refill_freelist() comes across more than nref_dirt dirty buffers, it
    will wake up bdflush.
   
age_buffer, age_super
    Finally, the age_buffer and age_super parameters govern the maximum time
    Linux waits before writing out a dirty buffer to disk. The value is
    expressed in jiffies (clockticks), the number of jiffies per second is
    100. Age_buffer is the maximum age for data blocks, while age_super is
    for filesystems meta data.
   
buffermem
    The three values in this file control how much memory should be used for
    buffer memory. The percentage is calculated as a percentage of total
    system memory.
   
   
        The values are:
       
    min_percent
        This is the minimum percentage of memory that should be spent on
        buffer memory.
       
    borrow_percent
          When Linux is short on memory, and the buffer cache uses more than
        it has been allotted, the memory management (MM) subsystem will prune
        the buffer cache more heavily than other memory to compensate.
       
    max_percent
        This is the maximum amount of memory that can be used for buffer
        memory.
       
   
   
freepages
   
        This file contains three values: min, low and high:
       
    min
        When the number of free pages in the system reaches this number, only
        the kernel can allocate more memory.
       
    low
        If the number of free pages falls below this point, the kernel starts
        swapping aggressively.
       
    high
          The kernel tries to keep up to this amount of memory free; if
        memory falls below this point, the kernel starts gently swapping in
        the hopes that it never has to do really aggressive swapping.
       
   
   
kswapd
    Kswapd is the kernel swap out daemon. That is, kswapd is that piece of
    the kernel that frees memory when it gets fragmented or full. Since every
    system is different, you'll probably want some control over this piece of
    the system.
   
   
        The file contains three numbers:
       
    tries_base
        The maximum number of pages kswapd tries to free in one round is
        calculated from this number. Usually this number will be divided by 4
        or 8 (see mm/vmscan.c), so it isn't as big as it looks. When you need
        to increase the bandwidth to/from swap, you'll want to increase this
        number.
       
    tries_min
        This is the minimum number of times kswapd tries to free a page each
        time it is called. Basically it's just there to make sure that kswapd
        frees some pages even when it's being called with minimum priority.
       
    swap_cluster
        This is probably the greatest influence on system performance.
        swap_cluster is the number of pages kswapd writes in one turn. You'll
        want this value to be large so that kswapd does its I/O in large
        chunks and the disk doesn't have to seek as often, but you don't want
        it to be too large since that would flood the request queue.
       
   
   
overcommit_memory
    This file contains one value. The following algorithm is used to decide
    if there's enough memory: if the value of overcommit_memory is positive,
    then there's always enough memory. This is a useful feature, since
    programs often malloc() huge amounts of memory 'just in case', while they
    only use a small part of it. Leaving this value at 0 will lead to the
    failure of such a huge malloc(), when in fact the system has enough
    memory for the program to run. On the other hand, enabling this feature
    can cause you to run out of memory and thrash the system to death, so
    large and/or important servers will want to set this value to 0.
   
pagecache
    This file does exactly the same job as buffermem, only this file controls
    the amount of memory allowed for memory mapping and generic caching of
    files. You don't want the minimum level to be too low, otherwise your
    system might thrash when memory is tight or fragmentation is high.
   
pagetable_cache
    The kernel keeps a number of page tables in a per-processor cache (this
    helps a lot on SMP systems). The cache size for each processor will be
    between the low and the high value. On a low-memory, single CPU system,
    you can safely set these values to 0 so you don't waste memory. It is
    used on SMP systems so that the system can perform fast pagetable
    allocations without having to acquire the kernel memory lock. For large
    systems, the settings are probably fine. For normal systems they won't
    hurt a bit. For small systems ( less than 16MB ram) it might be
    advantageous to set both values to 0.
   
swapctl
   
        This file contains no less than 8 variables. All of these values are
        used by kswapd. The first four variables sc_max_page_age,
        sc_page_advance, sc_page_decline and sc_page_initial_age are used to
        keep track of Linux's page aging. Page ageing is a bookkeeping method
        to track which pages of memory are often used, and which pages can be
        swapped out without consequences.
       
   
        When a page is swapped in, it starts at sc_page_initial_age (default
        3) and when the page is scanned by kswapd, its age is adjusted
        according to the following scheme.
       
   
        If the page was used since the last time we scanned, its age is
        increased by sc_page_advance (default 3). Where the maximum value is
        given by sc_max_page_age (default 20). Otherwise (meaning it wasn't
        used) its age is decreased by sc_page_decline (default 1).
       
   
        When a page reaches age 0, it's ready to be swapped out.
       
   
        The variables sc_age_cluster_fract, sc_age_cluster_min,
        sc_pageout_weight and sc_bufferout_weight, can be used to control
        kswapd's aggressiveness in swapping out pages.
       
   
        Sc_age_cluster_fract is used to calculate how many pages from a
        process are to be scanned by kswapd. The formula used is
       
   
        (sc_age_cluster_fract divided by 1024) times resident set size
       
   
        So if you want kswapd to scan the whole process, sc_age_cluster_fract
        needs to have a value of 1024. The minimum number of pages kswapd
        will scan is represented by sc_age_cluster_min, which is done so that
        kswapd will also scan small processes. The values of
        sc_pageout_weight and sc_bufferout_weight are used to control how
        many tries kswapd will make in order to swap out one page/buffer.
        These values can be used to fine-tune the ratio between user pages
        and buffer/cache memory. When you find that your Linux system is
        swapping out too many process pages in order to satisfy buffer memory
        demands, you may want to either increase sc_bufferout_weight, or
        decrease the value of sc_pageout_weight.
       
   
   
/proc/sys/dev
    Device specific parameters. Currently there is only support for CDROM
    drives, and for those, there is only one read-only file containing
    information about the CD-ROM drives attached to the system: >cat /proc/
    sys/dev/cdrom/info CD-ROM information, Id: cdrom.c 2.55 1999/04/25 drive
    name: sr0 hdb drive speed: 32 40 drive # of slots: 1 0 Can close tray: 1
    1 Can open tray: 1 1 Can lock tray: 1 1 Can change speed: 1 1 Can select
    disk: 0 1 Can read multisession: 1 1 Can read MCN: 1 1 Reports media
    changed: 1 1 Can play audio: 1 1 You see two drives, sr0 and hdb, along
    with a list of their features.
   
SUNRPC
     
   
    /proc/sys/sunrpc
          This directory contains four files, which enable or disable
        debugging for the RPC functions NFS, NFS-daemon, RPC and NLM. The
        default values are 0. They can be set to one to turn debugging on.
        (The default value is 0 for each)
       
    /proc/sys/net
          The interface to the networking parts of the kernel is located in /
        proc/sys/net. The following table shows all possible subdirectories.
        You may see only some of them, depending on your kernel's
        configuration. Our main focus will be on IP networking since AX15,
        X.25, and DEC Net are only minor players in the Linux world. Should
        you wish review the online documentation and the kernel source to get
        a detailed view of the parameters for those protocols not covered
        here. In this section we'll discuss the subdirectories listed above.
        As default values are suitable for most needs, there is no need to
        change these values.
       
   
   
GENERAL PARAMETERS
     
   
    /proc/sys/net/core
          Network core options
       
    rmem_default
        The default setting of the socket receive buffer in bytes.
       
    rmem_max
        The maximum receive socket buffer size in bytes.
       
    wmem_default
        The default setting (in bytes) of the socket send buffer.
       
    wmem_max
        The maximum send socket buffer size in bytes.
       
    message_burst and message_cost
          These parameters are used to limit the warning messages written to
        the kernel log from the networking code. They enforce a rate limit to
        make a denial-of-service attack impossible. A higher message_cost
        factor, results in fewer messages that will be written. Message_burst
        controls when messages will be dropped. The default settings limit
        warning messages to one every five seconds.
       
    netdev_max_backlog
          Maximum number of packets, queued on the INPUT side, when the
        interface receives packets faster than kernel can process them.
       
    optmem_max
        Maximum ancillary buffer size allowed per socket. Ancillary data is a
        sequence of struct cmsghdr structures with appended data.
       
   
   
UNIX DOMAIN SOCKETS
     
   
    /proc/sys/net/unix
          Parameters for Unix domain sockets
       
   
        There are only two files in this subdirectory. They control the
        delays for deleting and destroying socket descriptors.
       
   
   
IPv4
    /proc/sys/net/ipv4
        IPV4 settings. IP version 4 is still the most used protocol in Unix
        networking. It will be replaced by IP version 6 in the next couple of
        years, but for the moment it's the de facto standard for the internet
        and is used in most networking environments around the world. Because
        of the importance of this protocol, we'll have a deeper look into the
        subtree controlling the behavior of the Ipv4 subsystem of the Linux
        kernel.
       
   
        Let's start with the entries in /proc/sys/net/ipv4.
       
   
   
ICMP settings
     
   
    icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
        Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO
        requests, or just those to broadcast and multicast addresses.
       
   
        Please note that if you accept ICMP echo requests with a broadcast/
        multi\-cast destination address your network may be used as an
        exploder for denial of service packet flooding attacks to other
        hosts.
       
    icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and
        icmp_timeexeed_rate
          Sets limits for sending ICMP packets to specific targets. A value
        of zero disables all limiting. Any positive value sets the maximum
        package rate in hundredth of a second (on Intel systems).
       
   
   
IP settings
     
   
    ip_autoconfig
        This file contains the number one if the host received its IP
        configuration by RARP, BOOTP, DHCP or a similar mechanism. Otherwise
        it is zero.
       
    ip_default_ttl
        TTL (Time To Live) for IPv4 interfaces. This is simply the maximum
        number of hops a packet may travel.
       
    ip_dynaddr
          Enable dynamic socket address rewriting on interface address
        change. This is useful for dialup interface with changing IP
        addresses.
       
    ip_forward
        Enable or disable forwarding of IP packages between interfaces.
        Changing this value resets all other parameters to their default
        values. They differ if the kernel is configured as host or router.
       
    ip_local_port_range
        Range of ports used by TCP and UDP to choose the local port. Contains
        two numbers, the first number is the lowest port, the second number
        the highest local port. Default is 1024-4999. Should be changed to
        32768-61000 for high-usage systems.
       
    ip_no_pmtu_disc
          Global switch to turn path MTU discovery off. It can also be set on
        a per socket basis by the applications or on a per route basis.
       
    ip_masq_debug
        Enable/disable debugging of IP masquerading.
       
   
   
IP fragmentation settings
     
   
    ipfrag_high_trash and ipfrag_low_trash
        Maximum memory used to reassemble IP fragments. When
        ipfrag_high_thrash bytes of memory is allocated for this purpose, the
        fragment handler will toss packets until ipfrag_low_thrash is
        reached.
       
    ipfrag_time
          Time in seconds to keep an IP fragment in memory.
       
   
   
TCP settings
     
   
    tcp_ecn
          This file controls the use of the ECN bit in the IPv4 headers, this
        is a new feature about Explicit Congestion Notification, but some
        routers and firewalls block traffic that has this bit set, so it
        could be necessary to echo 0 to /proc/sys/net/ipv4/tcp_ecn, if you
        want to talk to this sites. For more info you could read RFC2481.
       
    tcp_retrans_collapse
        Bug-to-bug compatibility with some broken printers. On retransmit,
        try to send larger packets to work around bugs in certain TCP stacks.
        Can be turned off by setting it to zero.
       
    tcp_keepalive_probes
        Number of keep alive probes TCP sends out, until it decides that the
        connection is broken.
       
    tcp_keepalive_time
          How often TCP sends out keep alive messages, when keep alive is
        enabled. The default is 2 hours.
       
    tcp_syn_retries
        Number of times initial SYNs for a TCP connection attempt will be
        retransmitted. Should not be higher than 255. This is only the
        timeout for outgoing connections, for incoming connections the number
        of retransmits is defined by tcp_retries1.
       
    tcp_sack
        Enable select acknowledgments after RFC2018.
       
    tcp_timestamps
        Enable timestamps as defined in RFC1323.
       
    tcp_stdurg
        Enable the strict RFC793 interpretation of the TCP urgent pointer
        field. The default is to use the BSD compatible interpretation of the
        urgent pointer pointing to the first byte after the urgent data. The
        RFC793 interpretation is to have it point to the last byte of urgent
        data. Enabling this option may lead to interoperability problems.
        Disabled by default.
       
    tcp_syncookies
        Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send
        out syncookies when the syn backlog queue of a socket overflows. This
        is to ward off the common 'syn flood attack'. Disabled by default.
        Note that the concept of a socket backlog is abandoned. This means
        the peer may not receive reliable error messages from an over loaded
        server with syncookies enabled.
       
    tcp_window_scaling
        Enable window scaling as defined in RFC1323.
       
    tcp_fin_timeout
        The length of time in seconds it takes to receive a final FIN before
        the socket is always closed. This is strictly a violation of the TCP
        specification, but required to prevent denial-of-service attacks.
       
    tcp_max_ka_probes
        Indicates how many keep alive probes are sent per slow timer run.
        Should not be set too high to prevent bursts.
       
    tcp_max_syn_backlog
        Length of the per socket backlog queue. Since Linux 2.2 the backlog
        specified in listen(2) only specifies the length of the backlog queue
        of already established sockets. When more connection requests arrive
        Linux starts to drop packets. When syncookies are enabled the packets
        are still answered and the maximum queue is effectively ignored.
       
    tcp_retries1
        Defines how often an answer to a TCP connection request is
        retransmitted before giving up.
       
    tcp_retries2
        Defines how often a TCP packet is retransmitted before giving up.
       
   
   
/proc/sys/net/ipv4/conf
     
   
   
        Here you'll find one subdirectory for each interface the system knows
        about and one directory called all. Changes in the all subdirectory
        affect all interfaces, whereas changes in the other subdirectories
        affect only one interface. All directories have the same entries:
       
    accept_redirects
        This switch decides if the kernel accepts ICMP redirect messages or
        not. The default is 'yes' if the kernel is configured for a regular
        host and 'no' for a router configuration.
       
    accept_source_route
        Should source routed packages be accepted or declined. The default is
        dependent on the kernel configuration. It's 'yes' for routers and
        'no' for hosts.
       
    bootp_relay
          Accept packets with source address 0.b.c.d with destinations not to
        this host as local ones. It is supposed that a BOOTP relay daemon
        will catch and forward such packets. The default is 0.
       
    forwarding
        Enable or disable IP forwarding on this interface.
       
    log_martians
        Log packets with source addresses with no known route to kernel log.
       
    mc_forwarding
        Do multicast routing. The kernel needs to be compiled with
        CONFIG_MROUTE and a multicast routing daemon is required.
       
    proxy_arp
        Does (1) or does not (0) perform proxy ARP.
       
    rp_filter
        Integer value determines if a source validation should be made. 1
        means yes, 0 means no. Disabled by default, but local/broadcast
        address spoofing is always on. If you set this to 1 on a router that
        is the only connection for a network to the net, it will prevent
        spoofing attacks against your internal networks (external addresses
        can still be spoofed), without the need for additional firewall
        rules.
       
    secure_redirects
        Accept ICMP redirect messages only for gateways, listed in default
        gateway list. Enabled by default.
       
    shared_media
          If it is not set the kernel does not assume that different subnets
        on this device can communicate directly. Default setting is 'yes'.
       
    send_redirects
        Determines whether to send ICMP redirects to other hosts.
       
    Routing settings
        The directory /proc/sys/net/ipv4/route contains several file to
        control routing issues.
       
    error_burst and error_cost
        These parameters are used to limit the warning messages written to
        the kernel log from the routing code. The higher the error_cost
        factor is, the fewer messages will be written. Error_burst controls
        when messages will be dropped. The default settings limit warning
        messages to one every five seconds.
       
    flush
          Writing to this file results in a flush of the routing cache.
       
    gc_elastic, gc_interval, gc_min_interval, gc_tresh, gc_timeout
        Values to control the frequency and behavior of the garbage
        collection algorithm for the routing cache.
       
    max_size
        Maximum size of the routing cache. Old entries will be purged once
        the cache reached has this size.
       
    max_delay, min_delay
        Delays for flushing the routing cache.
       
    redirect_load, redirect_number
          Factors which determine if more ICPM redirects should be sent to a
        specific host. No redirects will be sent once the load limit or the
        maximum number of redirects has been reached.
       
    redirect_silence
        Timeout for redirects. After this period redirects will be sent
        again, even if this has been stopped, because the load or number
        limit has been reached.
       
    /proc/sys/net/ipv4/neigh
        Network Neighbor handling. It contains settings about how to handle
        connections with direct neighbors (nodes attached to the same link).
        As we saw it in the conf directory, there is a default subdirectory
        which holds the default values, and one directory for each interface.
        The contents of the directories are identical, with the single
        exception that the default settings contain additional options to set
        garbage collection parameters.
       
   
        In the interface directories you'll find the following entries:
       
    base_reachable_time
        A base value used for computing the random reachable time value as
        specified in RFC2461.
       
    retrans_time
        The time, expressed in jiffies (1/100 sec), between retransmitted
        Neighbor Solicitation messages. Used for address resolution and to
        determine if a neighbor is unreachable.
       
    unres_qlen
          Maximum queue length for a pending arp request - the number of
        packets which are accepted from other layers while the ARP address is
        still resolved.
       
    anycast_delay
        Maximum for random delay of answers to neighbor solicitation messages
        in jiffies (1/100 sec). Not yet implemented (Linux does not have
        anycast support yet).
       
    ucast_solicit
        Maximum number of retries for unicast solicitation.
       
    mcast_solicit
        Maximum number of retries for multicast solicitation.
       
    delay_first_probe_time
        Delay for the first time probe if the neighbor is reachable. (see
        gc_stale_time)
       
    locktime
        An ARP/neighbor entry is only replaced with a new one if the old is
        at least locktime old. This prevents ARP cache thrashing.
       
    proxy_delay
        Maximum time (real time is random [0..proxytime]) before answering to
        an ARP request for which we have an proxy ARP entry. In some cases,
        this is used to prevent network flooding.
       
    proxy_qlen
          Maximum queue length of the delayed proxy arp timer. (see
        proxy_delay).
       
    app_solcit
        Determines the number of requests to send to the user level ARP
        daemon. Use 0 to turn off.
       
    gc_stale_time
        Determines how often to check for stale ARP entries. After an ARP
        entry is stale it will be resolved again (which is useful when an IP
        address migrates to another machine). When ucast_solicit is greater
        than 0 it first tries to send an ARP packet directly to the known
        host When that fails and mcast_solicit is greater than 0, an ARP
        request is broadcasted.
       
   
   
APPLETALK
     
   
    /proc/sys/net/appletalk
          Holds the Appletalk configuration data when Appletalk is loaded.
        The configurable parameters are:
       
    aarp-expiry-time
          The amount of time we keep an ARP entry before expiring it. Used to
        age out old hosts.
       
    aarp-resolve-time
          The amount of time we will spend trying to resolve an Appletalk
        address.
       
    aarp-retransmit-limit
          The number of times we will retransmit a query before giving up.
       
    aarp-tick-time
          Controls the rate at which expires are checked.
       
    /proc/net/appletalk
        Holds the list of active Appletalk sockets on a machine. The fields
        indicate the DDP type, the local address (in network:node format) the
        remote address, the size of the transmit pending queue, the size of
        the received queue (bytes waiting for applications to read) the state
        and the uid owning the socket.
       
    /proc/net/atalk_iface
        lists all the interfaces configured for appletalk. It shows the name
        of the interface, its Appletalk address, the network range on that
        address (or network number for phase 1 networks), and the status of
        the interface.
       
    /proc/net/atalk_route
        lists each known network route. It lists the target (network) that
        the route leads to, the router (may be directly connected), the route
        flags, and the device the route is using.
       
   
   
IPX
     
   
   
        The IPX protocol has no tunable values in proc/sys/net, it does,
        however, provide proc/net/ipx. This lists each IPX socket giving the
        local and remote addresses in Novell format (that is network:node:
        port). In accordance with the strange Novell tradition, everything
        but the port is in hex. Not_Connected is displayed for sockets that
        are not tied to a specific remote address. The Tx and Rx queue sizes
        indicate the number of bytes pending for transmission and reception.
        The state indicates the state the socket is in and the uid is the
        owning uid of the socket.
       
    ipx_interface
        Lists all IPX interfaces. For each interface it gives the network
        number, the node number, and indicates if the network is the primary
        network. It also indicates which device it is bound to (or Internal
        for internal networks) and the Frame Type if appropriate. Linux
        supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet
        framing for IPX.
       
    ipx_route
        Table holding a list of IPX routes. For each route it gives the
        destination network, the router node (or Directly) and the network
        address of the router (or Connected) for internal networks.
       
   
   
/proc/sysvipc
    Info of SysVIPC Resources (msg, sem, shm) (2.4)
   
/proc/tty
    Information about the available and actually used tty's can be found in
    the directory /proc/tty. You'll find entries for drivers and line
    disciplines in this directory.
   
/proc/tty/drivers
      list of drivers and their usage.
   
/proc/tty/ldiscs
    registered line disciplines.
   
/proc/tty/driver/serial
      usage statistic and status of single tty lines.
   
   
        To see which tty's are currently in use, you can simply look into the
        file /proc/tty/drivers:
       
   
          # cat /proc/tty/drivers                                            
          serial               /dev/cua        5  64-127 serial:callout      
          serial               /dev/ttyS       4  64-127 serial              
          pty_slave            /dev/pts      143   0-255 pty:slave           
          pty_master           /dev/ptm      135   0-255 pty:master          
          pty_slave            /dev/pts      142   0-255 pty:slave           
          pty_master           /dev/ptm      134   0-255 pty:master          
          pty_slave            /dev/pts      141   0-255 pty:slave           
          pty_master           /dev/ptm      133   0-255 pty:master          
          pty_slave            /dev/pts      140   0-255 pty:slave           
          pty_master           /dev/ptm      132   0-255 pty:master          
          pty_slave            /dev/pts      139   0-255 pty:slave           
          pty_master           /dev/ptm      131   0-255 pty:master          
          pty_slave            /dev/pts      138   0-255 pty:slave           
          pty_master           /dev/ptm      130   0-255 pty:master          
          pty_slave            /dev/pts      137   0-255 pty:slave           
          pty_master           /dev/ptm      129   0-255 pty:master          
          pty_slave            /dev/pts      136   0-255 pty:slave           
          pty_master           /dev/ptm      128   0-255 pty:master          
          pty_slave            /dev/ttyp       3   0-255 pty:slave           
          pty_master           /dev/pty        2   0-255 pty:master          
          /dev/vc/0            /dev/vc/0       4       0 system:vtmaster     
          /dev/ptmx            /dev/ptmx       5       2 system              
          /dev/console         /dev/console    5       1 system:console      
          /dev/tty             /dev/tty        5       0 system:/dev/tty     
          unknown              /dev/vc/%d      4    1-63 console             
                                                                             
       
   
        Note that while the above files tend to be easily readable text
        files, they can sometimes be formatted in a way that is not easily
        digestible. There are many commands that do little more than read the
        above files and format them for easier understanding. For example,
        the free program reads /proc/meminfo and converts the amounts given
        in bytes to kilobytes (and adds a little more information, as well).
       
   
   
/proc/uptime
    The time the system has been up.
   
/proc/version
      The kernel version.
   
/proc/video
    BTTV info of video resources.
   

-----------------------------------------------------------------------------
1.15. /root

  This is the home directory of the System Administrator, 'root'. This may be
somewhat confusing ('root on root') but in former days, '/' was root's home
directory (hence the name of the Administrator account). To keep things
tidier, 'root' got his own home directory. Why not in '/home'? Because '/
home' is often located on a different partition or even on another system and
would thus be inaccessible to 'root' when - for some reason - only '/' is
mounted.

  The FSSTND merely states that this is the recommended location for the home
directory of 'root'. It is left up to the end user to determine the home
directory of 'root'. However, the FSSTND also says that:

 
                                                                              
  If the home directory of the root account is not stored on the root         
  partition it will be necessary to make certain it will default to           
  / if it can not be located.                                                 
                                                                              
  We recommend against using the root account for tasks that can be           
  performed as an unprivileged user, and that it be used solely for           
  system administration. For this reason, we recommend that subdirectories    
  for mail and other applications not appear in the root account's home       
  directory, and that mail for administration roles such as root, postmaster, 
  and webmaster be forwarded to an appropriate user.                          
                                                                              
-----------------------------------------------------------------------------

1.16. /sbin

  Linux discriminates between 'normal' executables and those used for system
maintenance and/or administrative tasks. The latter reside either here or -
the less important ones - in /usr/sbin. Locally installed system
administration programs should be placed into /usr/local/sbin.

  Programs executed after /usr is known to be mounted (when there are no
problems) are generally placed into /usr/sbin. This directory contains
binaries that are essential to the working of the system. These include
system administration as well as maintenance and hardware configuration
programs. You may find lilo, fdisk, init, ifconfig, etc.... here.

  Another directory that contains system binaries is /usr/sbin. This
directory contains other binaries of use to the system administrator. This is
where you will find the network daemons for your system along with other
binaries that (generally) only the system administrator has access to, but
which are not required for system maintenance and repair. Normally, these
directories are never part of normal user's $PATHs, only of roots (PATH is an
environment variable that controls the sequence of locations that the system
will attempt to look in for commands).

  The FSSTND states that:

 
                                                                             
  /sbin should contain only binaries essential for booting, restoring,       
  recovering, and/or repairing the system in addition to the binaries        
  in /bin.                                                                   
                                                                             

  A particular eccentricity of the Linux filesystem hierarchy is that
originally /sbin binaries were kept in /etc.

 
  Deciding what things go into "sbin" directories is simple: if a normal     
  (not a system administrator) user will ever run it directly, then it       
  must be placed in one of the "bin" directories. Ordinary users should      
  not have to place any of the sbin directories in their path.               
                                                                             
  For example, files such as chfn which users only occasionally use must     
  still be placed in /usr/bin. ping, although it is absolutely necessary     
  for root (network recovery and diagnosis) is often used by users and       
  must live in /bin for that reason.                                         
                                                                             
  We recommend that users have read and execute permission for everything    
  in /sbin except, perhaps, certain setuid and setgid programs. The          
  division between /bin and /sbin was not created for security reasons or    
  to prevent users from seeing the operating system, but to provide a        
  good partition between binaries that everyone uses and ones that are       
  primarily used for administration tasks. There is no inherent security     
  advantage in making /sbin off-limits for users.                            
                                                                             

  FSSTND compliance requires that the following commands, or symbolic links
to commands, are required in /sbin.

 
       shutdown Command to bring the system down.                            
                                                                             

  The following files, or symbolic links to files, must be in /sbin if the
corresponding subsystem is installed:

 
       fastboot   Reboot the system without checking the disks (optional)                   
       fasthalt   Stop the system without checking the disks (optional)                     
       fdisk      Partition table manipulator (optional)                                    
       fsck       File system check and repair utility (optional)                           
       fsck.*     File system check and repair utility for a specific filesystem (optional) 
       getty      The getty program (optional)                                              
       halt       Command to stop the system (optional)                                     
       ifconfig   Configure a network interface (optional)                                  
       init       Initial process (optional)                                                
       mkfs       Command to build a filesystem (optional)                                  
       mkfs.*     Command to build a specific filesystem (optional)                         
       mkswap     Command to set up a swap area (optional)                                  
       reboot     Command to reboot the system (optional)                                   
       route      IP routing table utility (optional)                                       
       swapon     Enable paging and swapping (optional)                                     
       swapoff    Disable paging and swapping (optional)                                    
       update     Daemon to periodically flush filesystem buffers (optional)                
                                                                                            
-----------------------------------------------------------------------------

1.17. /usr

 /usr usually contains by far the largest share of data on a system. Hence,
this is one of the most important directories in the system as it contains
all the user binaries, their documentation, libraries, header files, etc....
X and its supporting libraries can be found here. User programs like telnet,
ftp, etc.... are also placed here. In the original Unix implementations, /usr
was where the home directories of the users were placed (that is to say, /usr
/someone was then the directory now known as /home/someone). In current
Unices, /usr is where user-land programs and data (as opposed to 'system
land' programs and data) are. The name hasn't changed, but it's meaning has
narrowed and lengthened from "everything user related" to "user usable
programs and data". As such, some people may now refer to this directory as
meaning 'User System Resources' and not 'user' as was originally intended.

 
/usr is shareable, read-only data. That means that /usr should                 
be shareable between various FHS-compliant hosts and must not be written to.   
Any information that is host-specific or varies with time is stored elsewhere. 
                                                                               
Large software packages must not use a direct subdirectory under the /usr      
hierarchy.                                                                     

/usr/X11R6
     
   
   
         Another large subdirectory structure begins here, containing
        libraries, executables, docs, fonts and much more concerning the X
        Window System. Its inclusion here is somewhat inconsistent and so is
        the difference between '/usr' and '/usr/X11R6' directories. One would
        assume that programs that run on X only have their files in the '/usr
        /X11R6' hierarchy, while the others use '/usr'. Regrettably, it isn't
        so. KDE and GNOME put their files in the '/usr' hierarchy, whereas
        the window manager Window Maker uses '/usr/X11R6'. Documentation
        files for X11R6 are not in '/usr/X11R6/doc', but primarily in '/usr/
        X11R6/lib/X11/doc'. This mess is due to the fact that in contrast to
        other operating systems, the graphical desktop isn't an integral part
        of the system. Linux is still primarily used on servers, where
        graphical systems don't make sense.
       
   
         This hierarchy is reserved for the X Window System, version 11
        release 6, and related files. To simplify matters and make XFree86
        more compatible with the X Window System on other systems, the
        following symbolic links must be present if /usr/X11R6 exists:
       
   
          /usr/bin/X11 -> /usr/X11R6/bin                                     
          /usr/lib/X11 -> /usr/X11R6/lib/X11                                 
          /usr/include/X11 -> /usr/X11R6/include/X11                         
       
   
         In general, software must not be installed or managed via the above
        symbolic links. They are intended for utilization by users only. The
        difficulty is related to the release version of the X Window System -
        in transitional periods, it is impossible to know what release of X11
        is in use.
       
   
   
/usr/X11R6/bin
     XFree86 system binaries. These are necessary for the initialisation,
    configuration and running of the X windowing system. X, xf86config,
    xauth, xmodmap and even xpenguin are located here.
   
/usr/X11R6/include
     XFree86 system header files. There are required for the compilation of
    some applications that utilise the X toolkit.
   
/usr/X11R6/lib
     XFree86 system libraries.
   
/usr/X11R6/lib/modules
     XFree86 system modules. These are the modules that X loads upon startup.
    Without these modules video4linux, DRI and GLX extensions and drivers for
    certain input devices would cease to function.
   
/usr/X11R6/lib/X11/fonts
     XFree86 system fonts. Fonts that are utilised by 'xfs' (the X Font
    Server) and programs of that ilk.
   
/usr/bin
     This directory contains the vast majority of binaries on your system.
    Executables in this directory vary widely. For instance vi, gcc,
    gnome-session and mozilla and are all found here.
   
/usr/doc
     The central documentation directory. Documentation is actually located
    in /usr/share/doc and linked from here.
   
/usr/etc
     Theoretically, that's another directory for configuration files.
    Virtually unused now.
   
/usr/games
     Once upon a time, this directory contained network games files. Rarely
    used now.
   
/usr/include
     The directory for 'header files', needed for compiling user space source
    code.
   
/usr/include/'package-name'
     Application specific header files.
   
/usr/info
     This directory used to contain the files for the info documentation
    system. Now they are in '/usr/share/info'.
   
/usr/lib
     This directory contains program libraries. Libraries are collections of
    frequently used program routines.
   
/usr/local
     The original idea behind '/usr/local' was to have a separate ('local') '
    /usr' directory on every machine besides '/usr', which might be just
    mounted read-only from somewhere else. It copies the structure of '/usr'.
    These days, '/usr/local' is widely regarded as a good place in which to
    keep self-compiled or third-party programs. The /usr/local hierarchy is
    for use by the system administrator when installing software locally. It
    needs to be safe from being overwritten when the system software is
    updated. It may be used for programs and data that are shareable amongst
    a group of hosts, but not found in /usr. Locally installed software must
    be placed within /usr/local rather than /usr unless it is being installed
    to replace or upgrade software in /usr.
   
/usr/man
     It once held the man pages. It has been moved to /usr/share/man.
   
/usr/sbin
     This directory contains programs for administering a system, meant to be
    run by 'root'. Like '/sbin', it's not part of a user's $PATH. Examples of
    included binaries here are chroot, useradd, in.tftpd and pppconfig.
   
/usr/share
     This directory contains 'shareable', architecture-independent files
    (docs, icons, fonts etc). Note, however, that '/usr/share' is generally
    not intended to be shared by different operating systems or by different
    releases of the same operating system. Any program or package which
    contains or requires data that doesn't need to be modified should store
    that data in '/usr/share' (or '/usr/local/share', if installed locally).
    It is recommended that a subdirectory be used in /usr/share for this
    purpose."
   
/usr/share/doc
     Location of package specific documentation files. These directories
    often contain useful information that might not be in the man pages. They
    may also contain templates and configuration files for certain utilities
    making configuration that much easier.
   
/usr/share/info
     Location of 'info' pages. This style of documentation seems to be
    largely ignored now. Manual pages are in far greater favour.
   
/usr/share/man
     Manual pages. They are organised into 8 sections, which are explained
    below.
   
   
         
        man1: User programs                                                      
        Manual pages that describe publicly accessible commands are contained    
        in this chapter. Most program documentation that a user will need to     
        use is located here.                                                     
                                                                                 
        man2: System calls                                                       
        This section describes all of the system calls (requests for the kernel  
        to perform operations).                                                  
                                                                                 
        man3: Library functions and subroutines                                  
        Section 3 describes program library routines that are not direct calls   
        to kernel services. This and chapter 2 are only really of interest to    
        programmers.                                                             
                                                                                 
        man4: Special files                                                      
        Section 4 describes the special files, related driver functions, and     
        networking support available in the system. Typically, this includes     
        the device files found in /dev and the kernel interface to networking    
        protocol support.                                                        
                                                                                 
        man5: File formats                                                       
        The formats for many data files are documented in the section 5. This    
        includes various include files, program output files, and system files.  
                                                                                 
        man6: Games                                                              
        This chapter documents games, demos, and generally trivial programs.     
        Different people have various notions about how essential this is.       
                                                                                 
        man7: Miscellaneous Manual pages that are difficult to classify are      
        designated as being section 7. The troff and other text processing       
        macro packages are found here.                                           
                                                                                 
        man8: System administration Programs used by system administrators       
        for system operation and maintenance are documented here. Some of        
        these programs are also occasionally useful for normal users.            
       
   
   
/usr/src
     The 'linux' sub-directory holds the Linux kernel sources, header-files
    and documentation.
   
/usr/src/RPM
     RPM provides a substructure for building RPMs from SRPMs. Organisation
    of this branch is fairly logical with packages being organised according
    to a package's architecture.
   
/usr/src/RPM/BUILD
     A temporary store for RPM binary files that are being built from source
    code.
   
/usr/src/RPM/RPMS/athlon, /usr/src/RPM/RPMS/i386, /usr/src/RPM/RPMS/i486, /
    usr/src/RPM/RPMS/i586, /usr/src/RPM/RPMS/i686, /usr/src/RPM/RPMS/noarch
     These directories contain architecture dependant RPM source files.
   
/usr/src/RPM/SOURCES
     This directory contains the source TAR files, patches, and icon files
    for software to be packaged.
   
/usr/src/RPM/SPECS
     RPM SPEC files. A SPEC file is a file that contains information as well
    as scripts that are necessary to build a package.
   
/usr/src/RPM/SRPMS
     Contains the source RPM files which result from a build.
   
/usr/src/linux
    Contains the source code for the Linux kernel.
   
/usr/src/linux/.config
     The last kernel source configuration. This file is normally created
    through the 'make config', 'make menuconfig' or 'make xconfig' steps
    during kernel compilation.
   
/usr/src/linux/.depend, /usr/src/linux/.hdepend
     'make dep' checks the dependencies of the selections you made when you
    created your .config file. It ensures that the required files can be
    found and it builds a list that is to be used during compilation. Should
    this process be successful these two files are created.
   
/usr/src/linux/COPYING
     GNU License
   
/usr/src/linux/CREDITS
     A partial credits-file of people that have contributed to the Linux
    project. It is sorted by name and formatted to allow easy grepping and
    beautification by scripts. The fields are: name (N), email (E),
    web-address (W), PGP key ID and fingerprint (P), description (D), and
    snail-mail address (S).
   
/usr/src/linux/MAINTAINERS
     List of maintainers and details on how to submit kernel changes.
   
/usr/src/linux/Makefile
     Contains data necessary for compilation of a working kernel. It allows
    developers and end-users to compile a kernel with a few simple steps (ie.
    make dep, make clean, make bzImage, make modules, make modules_install)
    and also not have to worry about re-compiling everything from scratch if
    parts of it have already been done so and are up to date.
   
/usr/src/linux/README
     These are the release notes for Linux version 2.4. Read them carefully,
    as they tell you what this is all about, explain how to install the
    kernel, and what to do if something goes wrong.
   
/usr/src/linux/REPORTING-BUGS
     A suggested procedure for reporting Linux bugs. You aren't obliged to
    use the bug reporting format, it is provided as a guide to the kind of
    information that can be useful to developers - no more.
   
/usr/src/linux/Rules.make
     This file contains rules which are shared between multiple Makefiles.
   
/usr/src/linux/Documentation
    Contains documentation that may be necessary in order to re-compile a
    kernel. However, it also provides quite a lot of information about your
    Linux system in general as well. For those who wish to seek further
    information on the contents of this directory you may consult the /usr/
    src/linux/Documentation/00-INDEX file. Further, more detailed
    documentation may be found in /usr/src/linux/Documentation/Docbook. Of
    course, the contents of this directory is written in Docbook but may be
    converted to pdf, ps or html using the make targets of 'pdfdocs',
    'psdocs' and 'htmldocs' respectively.
   
/usr/tmp
     User space temporary files. This directory is not found on modern
    distributions at all and was most likely created as a consequence of
    Linux's UNIX heritage.
   

-----------------------------------------------------------------------------
1.18. /var

  Contains variable data like system logging files, mail and printer spool
directories, and transient and temporary files. Some portions of /var are not
shareable between different systems. For instance, /var/log, /var/lock, and /
var/run. Other portions may be shared, notably /var/mail, /var/cache/man, /
var/cache/fonts, and /var/spool/news. Why not put it into /usr? Because there
might be circumstances when you may want to mount /usr as read-only, e.g. if
it is on a CD or on another computer. '/var' contains variable data, i.e.
files and directories the system must be able to write to during operation,
whereas /usr should only contain static data. Some directories can be put
onto separate partitions or systems, e.g. for easier backups, due to network
topology or security concerns. Other directories have to be on the root
partition, because they are vital for the boot process. 'Mountable'
directories are: '/home', '/mnt', '/tmp', '/usr' and '/var'. Essential for
booting are: '/bin', '/boot', '/dev', '/etc', '/lib', '/proc' and '/sbin'.

 
If /var cannot be made a separate partition, it is often preferable to move /   
var out of the root partition and into the /usr partition. (This is sometimes   
done to reduce the size of the root partition or when space runs low in the     
root partition.) However, /var must not be linked to /usr because this makes    
separation of /usr and /var more difficult and is likely to create a naming     
conflict. Instead, link /var to /usr/var.                                       
                                                                                
Applications must generally not add directories to the top level of /var. Such  
directories should only be added if they have some system-wide implication, and 
in consultation with the FHS mailing list.                                      
                                                                                

/var/backups
    Directory containing backups of various key system files such as /etc/
    shadow, /etc/group, /etc/inetd.conf and dpkg.status. They are normally
    renamed to something like dpkg.status.0, group.bak, gshadow.bak,
    inetd.conf.bak, passwd.bak, shadow.bak
   
/var/cache
    Is intended for cached data from applications. Such data is locally
    generated as a result of time-consuming I/O or calculation. This data can
    generally be regenerated or be restored. Unlike /var/spool, files here
    can be deleted without data loss. This data remains valid between
    invocations of the application and rebooting of the system. The existence
    of a separate directory for cached data allows system administrators to
    set different disk and backup policies from other directories in /var.
   
/var/cache/fonts
    Locally-generated fonts. In particular, all of the fonts which are
    automatically generated by mktexpk must be located in appropriately-named
    subdirectories of /var/cache/ fonts.
   
/var/cache/man
    A cache for man pages that are formatted on demand. The source for manual
    pages is usually stored in /usr/share/man/; some manual pages might come
    with a pre-formatted version, which is stored in /usr/share/man/cat*
    (this is fairly rare now). Other manual pages need to be formatted when
    they are first viewed; the formatted version is then stored in /var/man
    so that the next person to view the same page won't have to wait for it
    to be formatted (/var/catman is often cleaned in the same way temporary
    directories are cleaned).
   
/var/cache/'package-name'
    Package specific cache data.
   
/var/cache/www
    WWW proxy or cache data.
   
/var/crash
    This directory will eventually hold system crash dumps. Currently, system
    crash dumps are not supported under Linux. However, development is
    already complete and is awaiting unification into the Linux kernel.
   
/var/db
    Data bank store.
   
/var/games
    Any variable data relating to games in /usr is placed here. It holds
    variable data that was previously found in /usr. Static data, such as
    help text, level descriptions, and so on, remains elsewhere though, such
    as in /usr/share/games. The separation of /var/games and /var/lib as in
    release FSSTND 1.2 allows local control of backup strategies,
    permissions, and disk usage, as well as allowing inter-host sharing and
    reducing clutter in /var/lib. Additionally, /var/games is the path
    traditionally used by BSD.
   
/var/lib
    Holds dynamic data libraries/files like the rpm/dpkg database and game
    scores. Furthermore, this hierarchy holds state information pertaining to
    an application or the system. State information is data that programs
    modify while they run, and that pertains to one specific host. Users
    shouldn't ever need to modify files in /var/lib to configure a package's
    operation. State information is generally used to preserve the condition
    of an application (or a group of inter-related applications) between
    invocations and between different instances of the same application. An
    application (or a group of inter-related applications) use a subdirectory
    of /var/lib for their data. There is one subdirectory, /var/lib/misc,
    which is intended for state files that don't need a subdirectory; the
    other subdirectories should only be present if the application in
    question is included in the distribution. /var/lib/'name' is the location
    that must be used for all distribution packaging support. Different
    distributions may use different names, of course.
   
/var/local
    Variable data for local programs (i.e., programs that have been installed
    by the system administrator) that are installed in /usr/local (as opposed
    to a remotely mounted '/var' partition). Note that even locally installed
    programs should use the other /var directories if they are appropriate,
    e.g., /var/lock.
   
/var/lock
    Many programs follow a convention to create a lock file in /var/lock to
    indicate that they are using a particular device or file. This directory
    holds those lock files (for some devices) and hopefully other programs
    will notice the lock file and won't attempt to use the device or file.
   
    Lock files should be stored within the /var/lock directory structure.
    Lock files for devices and other resources shared by multiple
    applications, such as the serial device lock files that were originally
    found in either /usr/spool/locks or /usr/spool/uucp, must now be stored
    in /var/lock. The naming convention which must be used is LCK.. followed
    by the base name of the device file. For example, to lock /dev/ttyS0 the
    file LCK..ttyS0 would be created. The format used for the contents of
    such lock files must be the HDB UUCP lock file format. The HDB format is
    to store the process identifier (PID) as a ten byte ASCII decimal number,
    with a trailing newline. For example, if process 1230 holds a lock file,
    it would contain the eleven characters: space, space, space, space,
    space, space, one, two, three, zero, and newline.
   
/var/log
    Log files from the system and various programs/services, especially login
    (/var/log/wtmp, which logs all logins and logouts into the system) and
    syslog (/var/log/messages, where all kernel and system program message
    are usually stored). Files in /var/log can often grow indefinitely, and
    may require cleaning at regular intervals. Something that is now normally
    managed via log rotation utilities such as 'logrotate'. This utility also
    allows for the automatic rotation compression, removal and mailing of log
    files. Logrotate can be set to handle a log file daily, weekly, monthly
    or when the log file gets to a certain size. Normally, logrotate runs as
    a daily cron job. This is a good place to start troubleshooting general
    technical problems.
   
/var/log/auth.log
    Record of all logins and logouts by normal users and system processes.
   
/var/log/btmp
    Log of all attempted bad logins to the system. Accessed via the lastb
    command.
   
/var/log/debug
    Debugging output from various packages.
   
/var/log/dmesg
    Kernel ring buffer. The content of this file is referred to by the dmesg
    command.
   
/var/log/gdm/
    GDM log files. Normally a subset of the last X log file. See /var/log/
    xdm.log for mode details.
   
/var/log/kdm.log
    KDM log file. Normally a subset of the last X log file. See /var/log/
    xdm.log for more details.
   
/var/log/messages
    System logs.
   
/var/log/pacct
    Process accounting is the bookkeeping of process activity. The raw data
    of process activity is maintained here. Three commands can be used to
    access the contents of this file dump-acct, sa (summary of process
    accounting) and lastcomm (list the commands executed on the system).
   
/var/log/utmp
    Active user sessions. This is a data file and as such it can not be
    viewed normally. A human-readable form can be created via the dump-utmp
    command or through the w, who or users commands.
   
/var/log/wtmp
    Log of all users who have logged into and out of the system. The last
    command can be used to access a human readable form of this file. It also
    lists every connection and run-level change.
   
/var/log/xdm.log
    XDM log file. Normally subset of the last X startup log and pretty much
    useless in light of the details the X logs is able to provide us with.
    Only consult this file if you have XDM specific issues otherwise just use
    the X logfile.
   
/var/log/XFree86.0.log, /var/log/XFree86.?.log
    X startup logfile. An excellent resource for uncovering problems with X
    configuration. Log files are numbered according to when they were last
    used. For example, the last log file would be stored in /var/log/
    XFree86.0.log, the next /var/log/XFree86.9.log, so on and so forth.
   
/var/log/syslog
    The 'system' log file. The contents of this file is managed via the
    syslogd daemon which more often than not takes care of all log
    manipulation on most systems.
   
/var/mail
    Contains user mailbox files. The mail files take the form /var/mail/
    'username' (Note that /var/mail may be a symbolic link to another
    directory). User mailbox files in this location are stored in the
    standard UNIX mailbox format. The reason for the location of this
    directory was to bring the FHS inline with nearly every UNIX
    implementation (it was previously located in /var/spool/mail). This
    change is important for inter-operability since a single /var/mail is
    often shared between multiple hosts and multiple UNIX implementations
    (despite NFS locking issues).
   
/var/opt
    Variable data of the program packages in /opt must be installed in /var/
    opt/'package-name', where 'package-name' is the name of the subtree in /
    opt where the static data from an add-on software package is stored,
    except where superceded by another file in /etc. No structure is imposed
    on the internal arrangement of /var/opt/'package-name'.
   
/var/run
    Contains the process identification files (PIDs) of system services and
    other information about the system that is valid until the system is next
    booted. For example, /var/run/utmp contains information about users
    currently logged in.
   
/var/spool
    Holds spool files, for instance for mail, news, and printing (lpd) and
    other queued work. Spool files store data to be processed after the job
    currently occupying a device is finished or the appropriate cron job is
    started. Each different spool has its own subdirectory below /var/spool,
    e.g., the cron tables are stored in /var/spool/cron/crontabs.
   
/var/tmp
    Temporary files that are large or that need to exist for a longer time
    than what is allowed for /tmp. (Although the system administrator might
    not allow very old files in /var/tmp either.)
   
/var/named
    Database for BIND. The Berkeley Internet Name Domain (BIND) implements an
    Internet domain name server. BIND is the most widely used name server
    software on the Internet, and is supported by the Internet Software
    Consortium, www.isc.org.
   
/var/yp
    Database for NIS (Network Information Services). NIS is mostly used to
    let several machines in a network share the same account information (eg.
    /etc/passwd). NIS was formerly called Yellow Pages (YP).
   

The following directories, or symbolic links to directories, are required in
/var for FSSTND compliance:

  /var/cache    Application cache data                                       
  /var/lib      Variable state information                                   
  /var/local    Variable data for /usr/local                                 
  /var/lock     Lock files                                                   
  /var/log      Log files and directories                                    
  /var/opt      Variable data for /opt                                       
  /var/run      Data relevant to running processes                           
  /var/spool    Application spool data                                       
  /var/tmp      Temporary files preserved between system reboots             
                                                                             

Several directories are 'reserved' in the sense that they must not be used
arbitrarily by some new application, since they would conflict with
historical and/or local practice. They are:

  /var/backups                                                               
  /var/cron                                                                  
  /var/msgs                                                                  
  /var/preserve                                                              
                                                                             

The following directories, or symbolic links to directories, must be in /var,
if the corresponding subsystem is installed:

  account   Process accounting logs (optional)                               
  crash     System crash dumps (optional)                                    
  games     Variable game data (optional)                                    
  mail      User mailbox files (optional)                                    
  yp        Network Information Service (NIS) database files (optional)      
                                                                             
-----------------------------------------------------------------------------

1.19. /srv

 
  /srv contains site-specific data which is served by this system.            
                                                                              
  This main purpose of specifying this is so that users may find              
  the location of the data files for particular service, and so that          
  services which require a single tree for readonly data, writable data       
  and scripts (such as cgi scripts) can be reasonably placed. Data that       
  is only of interest to a specific user should go in that users'             
  home directory.                                                             
                                                                              
  The methodology used to name subdirectories of /srv is unspecified as there 
  is currently no consensus on how this should be done. One method for        
  structuring data under /srv is by protocol, eg. ftp, rsync, www, and cvs.   
  On large systems it can be useful to structure /srv by administrative       
  context, such as /srv/physics/www, /srv/compsci/cvs, etc. This setup will   
  differ from host to host. Therefore, no program should rely on a specific   
  subdirectory structure of /srv existing or data necessarily being stored in 
  /srv. However /srv should always exist on FHS compliant systems and should  
  be used as the default location for such data.                              
                                                                              
  Distributions must take care not to remove locally placed files in these    
  directories without administrator permission.                               
                                                                              
  This is particularly important as these areas will often contain both       
  files initially installed by the distributor, and those added by the        
  administrator.                                                              
                                                                              
-----------------------------------------------------------------------------

1.20. /tmp

  This directory contains mostly files that are required temporarily. Many
programs use this to create lock files and for temporary storage of data. Do
not remove files from this directory unless you know exactly what you are
doing! Many of these files are important for currently running programs and
deleting them may result in a system crash. Usually it won't contain more
than a few KB anyway. On most systems, this directory is cleared out at boot
or at shutdown by the local system. The basis for this was historical
precedent and common practice. However, it was not made a requirement because
system administration is not within the scope of the FSSTND. For this reason
people and programs must not assume that any files or directories in /tmp are
preserved between invocations of the program. The reasoning behind this is
for compliance with IEEE standard P1003.2 (POSIX, part 2).

Glossary

 ARPA
     The Advanced Research and Projects Agency of the United States
    Department of Defense. Also known as DARPA (the "D" stands for
    "Defense"), it originated in the late 1960s and early 1970s the proposal
    and standards for the Internet. For this reason, the Internet was
    initially referred to as ARPANet, and connected the military with the
    various centers of research around the United States in a way that was
    intended to have a high degree of survivability against a nuclear attack.
   
 BASH
     The Bourne Again Shell and is based on the Bourne shell, sh, the
    original command interpreter.
   
 Bourne Shell
     The Bourne shell is the original Unix shell (command execution program,
    often called a command interpreter) that was developed at AT&T. Named for
    its developer, Stephen Bourne, the Bourne shell is also known by its
    program name, sh. The shell prompt (character displayed to indicate
    readiness for input) used is the $ symbol. The Bourne shell family
    includes the Bourne, Korn shell, bash, and zsh shells. Bourne Again Shell
    (bash) is the free version of the Bourne shell distributed with Linux
    systems. Bash is similar to the original, but has added features such as
    command line editing. Its name is sometimes spelled as Bourne Again
    SHell, the capitalized Hell referring to the difficulty some people have
    with it.
   
 CLI
     A CLI (command line interface) is a user interface to a computer's
    operating system or an application in which the user responds to a visual
    prompt by typing in a command on a specified line, receives a response
    back from the system, and then enters another command, and so forth. The
    MS-DOS Prompt application in a Windows operating system is an example of
    the provision of a command line interface. Today, most users prefer the
    graphical user interface (GUI) offered by Windows, Mac OS, BeOS, and
    others. Typically, most of today's Unix-based systems offer both a
    command line interface and a graphical user interface.
   
 core
     A core file is created when a program terminates unexpectedly, due to a
    bug, or a violation of the operating system's or hardware's protection
    mechanisms. The operating system kills the program and creates a core
    file that programmers can use to figure out what went wrong. It contains
    a detailed description of the state that the program was in when it died.
    If would like to determine what program a core file came from, use the
    file command, like this: $ file core That will tell you the name of the
    program that produced the core dump. You may want to write the maintainer
    (s) of the program, telling them that their program dumped core. To
    Enable or Disable Core Dumps you must use the ulimit command in bash, the
    limit command in tcsh, or the rlimit command in ksh. See the appropriate
    manual page for details. This setting affects all programs run from the
    shell (directly or indirectly), not the whole system. If you wish to
    enable or disable core dumping for all processes by default, you can
    change the default setting in /usr/include/linux/sched.h. Refer to
    definition of INIT_TASK, and look also in /usr/include/linux/resource.h.
    PAM support optimizes the system's environment, including the amount of
    memory a user is allowed. In some distributions this parameter is
    configurable in the /etc/security/limits.conf file. For more information,
    refer to the Linux Administrator's Security Guide.
   
 daemon
     A process lurking in the background, usually unnoticed, until something
    triggers it into action. For example, the \cmd{update} daemon wakes up
    every thirty seconds or so to flush the buffer cache, and the \cmd
    {sendmail} daemon awakes whenever someone sends mail.
   
 DARPA
     The Defense Advanced Research Projects Agency is the central research
    and development organization for the Department of Defense (DoD). It
    manages and directs selected basic and applied research and development
    projects for DoD, and pursues research and technology where risk and
    payoff are both very high and where success may provide dramatic advances
    for traditional military roles and missions.
   
 DHCP
     Dynamic Host Control Protocol, is a protocol like BOOTP (actually dhcpd
    includes much of the functionality of BOOTPD). It assigns IP addresses to
    clients based on lease times. DHCP is used extensively by Microsoft and
    more recently also by Apple. It is probably essential in any
    multi-platform environment.
   
 DNS
     Domain Name System translates Internet domain and host names to IP
    addresses. DNS implements a distributed database to store name and
    address information for all public hosts on the Net. DNS assumes IP
    addresses do not change (i.e., are statically assigned rather than
    dynamically assigned). The DNS database resides on a hierarchy of
    special-purpose servers. When visiting a Web site or other device on the
    Net, a piece of software called the DNS resolver (usually built into the
    network operating system) first contacts a DNS server to determine the
    server's IP address. If the DNS server does not contain the needed
    mapping, it will in turn forward the request to a DNS server at the next
    higher level in the hierarchy. After potentially several forwarding and
    delegation messages are sent within the DNS hierarchy, the IP address for
    the given host eventually is delivered to the resolver. DNS also includes
    support for caching requests and for redundancy. Most network operating
    systems allow one to enter the IP addresses of primary, secondary, and
    tertiary DNS servers, each of which can service initial requests from
    clients. Many ISPs maintain their own DNS servers and use DHCP to
    automatically assign the addresses of these servers to dial-in clients,
    so most home users need not be aware of the details behind DNS
    configuration. Registered domain names and addresses must be renewed
    periodically, and should a dispute occur between two parties over
    ownership of a given name, such as in trademarking, ICANN's Uniform
    Domain-Name Dispute-Resolution Policy can be invoked. Also known as
    Domain Name System, Domain Name Service, Domain Name Server.
   
 environment variable
     A variable that is available to any program that is started by the
    shell.
   
 ESD
     Enlightened Sound Daemon. This program is designed to mix together
    several digitized audio streams for playback by a single device.
   
 filesystem
     The methods and data structures that an operating system uses to keep
    track of files on a disk or partition; the way the files are organized on
    the disk. Also used to describe a partition or disk that is used to store
    the files or the type of the filesystem.
   
 FSSTND
     Often the group, which creates the Linux File System Structure document,
    or the document itself, is referred to as the 'FSSTND'. This is short for
    "file system standard". This document has helped to standardize the
    layout of file systems on Linux systems everywhere. Since the original
    release of the standard, most distributors have adopted it in whole or in
    part, much to the benefit of all Linux users. It is now often refered to
    as the FHS (Filesystem Hierarchy Standard) document though since its
    incorporation into the LSB (Linux Standards Base) Project.
   
 GUI
     Graphical User Interface. The use of pictures rather than just words to
    represent the input and output of a program. A program with a GUI runs
    under some windowing system (e.g. The X Window System, Microsoft Windows,
    Acorn RISC OS, NEXTSTEP). The program displays certain icons, buttons,
    dialogue boxes etc. in its windows on the screen and the user controls it
    mainly by moving a pointer on the screen (typically controlled by a
    mouse) and selecting certain objects by pressing buttons on the mouse
    while the pointer is pointing at them. Though Apple Computer would like
    to claim they invented the GUI with their Macintosh operating system, the
    concept originated in the early 1970s at Xerox's PARC laboratory.
   
 hard link
     A directory entry, which maps a filename to an inode, number. A file may
    have multiple names or hard links. The link count gives the number of
    names by which a file is accessible. Hard links do not allow multiple
    names for directories and do not allow multiple names in different
    filesystems.
   
 init
     'init' process is the first user level process started by the kernel.
    init has many important duties, such as starting getty (so that users can
    log in), implementing run levels, and taking care of orphaned processes.
    This chapter explains how init is configured and how you can make use of
    the different run levels. init is one of those programs that are
    absolutely essential to the operation of a Linux system, but that you
    still can mostly ignore. Usually, you only need to worry about init if
    you hook up serial terminals, dial-in (not dial-out) modems, or if you
    want to change the default run level. When the kernel has started (has
    been loaded into memory, has started running, and has initialized all
    device drivers and data structures and such), it finishes its own part of
    the boot process by starting a user level program, init. Thus, init is
    always the first process (its process number is always 1). The kernel
    looks for init in a few locations that have been historically used for
    it, but the proper location for it is /sbin/init. If the kernel can't
    find init, it tries to run /bin/sh, and if that also fails, the startup
    of the system fails. When init starts, it completes the boot process by
    doing a number of administrative tasks, such as checking filesystems,
    cleaning up /tmp, starting various services, and starting a getty for
    each terminal and virtual console where users should be able to log in.
    After the system is properly up, init restarts getty for each terminal
    after a user has logged out (so that the next user can log in). init also
    adopts orphan processes: when a process starts a child process and dies
    before its child, the child immediately becomes a child of init. This is
    important for various technical reasons, but it is good to know it, since
    it makes it easier to understand process lists and process tree graphs.
    init itself is not allowed to die. You can't kill init even with SIGKILL.
    There are a few variants of init available. Most Linux distributions use
    sysvinit (written by Miquel van Smoorenburg), which is based on the
    System V init design. The BSD versions of Unix have a different init. The
    primary difference is run levels: System V has them, BSD doesn't.
   
 inode
     An inode is the address of a disk block. When you see the inode
    information through ls, ls prints the address of the first block in the
    file. You can use this information to tell if two files are really the
    same file with different names (links). A file has several components: a
    name, contents, and administrative information such as permissions and
    modification times. The administrative information is stored in the inode
    (over the years, the hyphen fell out of "i-node"), along with essential
    system data such as how long it is, where on the disc the contents of the
    file are stored, and so on. There are three times in the inode: the time
    that the contents of the file were last modified (written); the time that
    the file was last used (read or executed); and the time that the inode
    itself was last changed, for example to set the permissions. Altering the
    contents of the file does not affect its usage time and changing the
    permissions affects only the inode change time. It is important to
    understand inodes, not only to appreciate the options on ls, but because
    in a strong sense the inodes are the files. All the directory hierarchy
    does is provide convenient names for files. The system's internal name
    for the file is its i-number: the number of the inode holding the file's
    information.
   
 kernel
     Part of an operating system that implements the interaction with
    hardware and the sharing of resources.
   
 libraries
     Executables should have no undefined symbols, only useful symbols; all
    useful programs refer to symbols they do not define (eg. printf or
    write). These references are resolved by pulling object files from
    libraries into the executable.
   
 link
     A symbolic link (alias in MacOS and shortcut under Windows) is a file
    that points to another file; this is a commonly used tool. A hard-link
    rarely created by the user, is a filename that points to a block of data
    that has several other filenames as well.
   
 man page
     Every version of UNIX comes with an extensive collection of online help
    pages called man pages (short for manual pages). The man pages are the
    authoritative documentation about your UNIX system. They contain complete
    information about both the kernel and all the utilities.
   
 MTA
     Mail Transfer Agents. Alongside the web, mail is the top reason for the
    popularity of the Internet. E-mail is an inexpensive and fast method of
    time-shifted messaging which, much like the Web, is actually based around
    sending and receiving plain text files. The protocol used is called the
    Simple Mail Transfer Protocol (SMTP). The server programs that implement
    SMTP to move mail from one server to another are called MTAs. Once upon a
    time users would have to Telnet into an SMTP server and use a command
    line mail program like 'mutt' or 'pine' to check their mail. Now, GUI
    based e-mail clients like Mozilla, Kmail and Outlook allow users to check
    their email off of a local SMTP sever. Additional protocols like POP3 and
    IMAP4 are used between the SMTP server and desktop mail client to allow
    clients to manipulate files on, and download from, their local mail
    server. The programs that implement POP3 and IMAP4 are called Mail
    Delivery Agents (MDAs). They are generally separate from MTAs.
   
 NFS
     Network File System, is the UNIX equivalent of Server Message Block
    (SMB). It is a way through which different machines can import and export
    local files between each other. Like SMB though, NFS sends information
    including user passwords unencrypted, so it's best to limit its usage to
    within your local network.
   
 operating system
     Software that shares a computer system's resources (processor, memory,
    disk space, network bandwidth, and so on) between users and the
    application programs they run. Controls access to the system to provide
    security.
   
 PAM
     Pluggable Authentication Modules. A suite of shared libraries that
    determine how a user will be authenticated. For example, conventionally
    UNIX users authenticate themselves by supplying a password at the
    password prompt after they have typed their name at the login prompt. In
    many circumstances, such as internal access to workstations, this simple
    form of authentication is considered sufficient. In other cases, more
    information is warranted. If a user wants to log in to an internal system
    from an external source, like the Internet, more or alternative
    information may be required - perhaps a one-time password. PAM provides
    this type of capability and much more. Most important, PAM modules allow
    you to configure your environment with the necessary level of security.
   
 PATH
     The shell looks for commands and programs in a list of file paths stored
    in the PATH environment variable. An environment variable stores
    information in a place where other programs and commands can access it.
    Environment variables store information such as the shell that you are
    using, your login name, and your current working directory. To see a list
    of all the environment variables currently defined; type 'set' at the
    prompt. When you type a command at the shell prompt, the shell will look
    for that command's program file in each directory listed in the PATH
    variable, in order. The first program found matching the command you
    typed will be run. If the command's program file is not in a directory
    listed in you PATH environment variable, the shell returns a "commands
    not found" error. By default, the shell does not look in your current
    working directory or your home directory for commands This is really a
    security mechanism so that you don't execute programs by accident. What
    if a malicious user put a harmful program called ls in your home
    directory? If you typed ls and the shell looked for the fake program in
    your home directory before the real program in the /bin directory, what
    do you think would happen? If you thought bad things, you are on the
    right track. Since your PATH doesn't have the current directory as one of
    its search locations, programs in your current directory must be called
    with an absolute path of a relative path specified as './program-name'.
    To see what directories are part of your PATH enter this command: # echo
    $PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/
    bin/X11
   
 pipes and sockets
     Special files that programs use to communicate with one another. They
    are rarely seen, but you might be able to see a socket or two in the /dev
    / directory.
   
 process identifier
     Shown in the heading of the ps command as PID. The unique number
    assigned to every process running in the system.
   
 rpc
     Remote Procedure Calls. It enables a system to make calls to programs
    such as NFS across the network transparently, enabling each system to
    interpret the calls as if they were local. In this case, it would make
    exported filesystems appear as thought they were local.
   
 set group ID (SGID)
     The SGID permission causes a script to run with its group set to the
    group of the script, rather than the group of the user who started it. It
    is normally considered extremely bad practice to run a program in this
    way as it can pose many security problems. Later versions of the Linux
    kernel will even prohibit the running of shell scripts that have this
    attribute set.
   
 set user ID (SUID)
     The SUID permission causes a script to run as the user who is the owner
    of the script, rather than the user who started it. It is normally
    considered extremely bad practice to run a program in this way as it can
    pose many security problems. Later versions of the Linux kernel will even
    prohibit the running of shell scripts that have this attribute set.
   
 signal
     Software interrupts sent to a program to indicate that an important
    event has occurred. The events can vary from user requests to illegal
    memory access errors. Some signals, like the interrupt signal, indicate
    that a user has asked the program to do something that is not in the
    usual flow of control.
   
 SSH
     The Secure Shell, or SSH, provides a way of running command line and
    graphical applications, and transferring files, over an encrypted
    connection, all that will be seen is junk. It is both a protocol and a
    suite of small command line applications, which can be used for various
    functions. SSH replaces the old Telnet application, and can be used for
    secure remote administration of machines across the Internet. However, it
    also has other features. SSH increases the ease of running applications
    remotely by setting up X permissions automatically. If you can log into a
    machine, it allows you to run a graphical application on it, unlike
    Telnet, which requires users to have an understanding of the X
    authentication mechanisms that are manipulated through the xauth and
    xhost commands. SSH also has inbuilt compression, which allows your
    graphic applications to run much faster over the network. SCP (Secure
    Copy) and SFTP (Secure FTP) allow transfer of files over the remote link,
    either via SSH's own command line utilities or graphical tools like
    Gnome's GFTP. Like Telnet, SSH is cross-platform. You can find SSH server
    and clients for Linux, Unix and all flavours of Windows, BeOS, PalmOS,
    Java and embedded Oses used in routers.
   
 STDERR
     Standard error. A special type of output used for error messages. The
    file descriptor for STDERR is 2.
   
 STDIN
     Standard input. User input is read from STDIN. The file descriptor for
    STDIN is 0.
   
 STDOUT
     Standard output. The output of scripts is usually to STDOUT. The file
    descriptor for STDOUT is 1.
   
 symbol table
     The part of an object table that gives the value of each symbol (usually
    as a section name and an offset) is called the symbol table. Executables
    may also have a symbol table, with this one giving the final values of
    the symbols. Debuggers use the symbol table to present addresses to the
    user in a symbolic, rather than a numeric form. It is possible to strip
    the symbol table from executables resulting in a smaller sized executable
    but this prevents meaningful debugging.
   
 symbolic link or soft link
     A special filetype, which is a small pointer file, allowing multiple
    names for the same file. Unlike hard links, symbolic links can be made
    for directories and can be made across filesystems. Commands that access
    the file being pointed to are said to follow the symbolic link. Commands
    that access the link itself do not follow the symbolic link.
   
 system call
     The services provided by the kernel to application programs, and the way
    in which they are invoked. See section 2 of the manual pages.
   
 system program
     Programs that implement high level functionality of an operating system,
    i.e., things that aren't directly dependent on the hardware. May
    sometimes require special privileges to run (e.g., for delivering
    electronic mail), but often just commonly thought of as part of the
    system (e.g., a compiler).
   
 tcp-wrappers
     Almost all of the services provided through inetd are invoked through
    tcp-wrappers by way of the tcp-wrappers daemon, tcpd. The tcp-wrappers
    mechanism provides access control list restrictions and logging for all
    service requests to the service it wraps. It may be used for either TCP
    or TCP services as long as the services are invoked through a central
    daemon process such as inetd. These programs log the client host name of
    incoming telnet, ftp, rsh, rlogin, finger etc.... requests. Security
    options are access control per host, domain and/or service; detection of
    host name spoofing or host address spoofing; booby traps to implement an
    early-warning system.
   
 ZSH
     Zsh was developed by Paul Falstad as a replacement for both the Bourne
    and C shell. It incorporates features of all the other shells (such as
    file name completion and a history mechanism) as well as new
    capabilities. Zsh is considered similar to the Korn shell. Falstad
    intended to create in zsh a shell that would do whatever a programmer
    might reasonably hope it would do. Zsh is popular with advanced users.
    Along with the Korn shell and the C shell, the Bourne shell remains among
    the three most widely used and is included with all UNIX systems. The
    Bourne shell is often considered the best shell for developing scripts.
   

-----------------------------------------------------------------------------
Appendix A. UNIX System V Signals

Symbol     Number   Action       Meaning                                     
SIGHUP     1        exit         Hangs up.                                   
SIGINT     2        exit         Interrupts.                                 
SIGQUIT    3        core dump    Quits.                                      
SIGILL     4        core dump    Illegal instruction.                        
SIGTRAP    5        core dump    Trace trap.                                 
SIGIOT     6        core dump    IOT instruction.                            
SIGEMT     7        core dump    MT instruction.                             
SIGFPE     8        core dump    Floating point exception.                   
SIGKILL    9        exit         Kills (cannot be caught or ignored).        
SIGBUS     10       core dump    Bus error.                                  
SIGSEGV    11       core dump    Segmentation violation.                     
SIGSYS     12       core dump    Bad argument to system call.                
SIGPIPE    13       exit         Writes on a pipe with no one to read it.    
SIGALRM    14       exit         Alarm clock.                                
SIGTERM    15       exit         Software termination signal.                
-----------------------------------------------------------------------------

Appendix B. Sources

  * The UNIX programming environment, Brian W. Kernighan, Rob Pike, Prentice
    Hall, New Jersey, 1984.
   

  * Newnes UNIX Pocket Book, Steve Heath, Butterworth-Heinemann, Great
    Britain, 1998.
   

  * Suse Linux Installation and Configuration, Nazeeh Amin El-Dirghami &
    Youssef A. Abu Kwaik, QUE Corporation, USA, 2000.
   

  * Inside Linux, Michael J. Tobler, New Riders Publishing, USA, 2001.
   

  * Linux in a Nutshell 2nd Edition, Ellen Siever, O'Reilly & Associates
    Inc., CA, USA, 1999
   

  * Using Caldera OpenLinux Special Edition, Allan Smart, Erik Ratcliffe, Tim
    Bird, David Bandel, QUE Corporation, USA, 1999.
   

  * Linux System Security (The Administrator's Guide to Open Source Security
    Tools), Scott Mann & Ellen L. Mitchell, Prentice-Hall, New-Jersey, 2000.
   

  * XFree86 For Linux (Uncommon Solutions for the Technical Professional),
    Aron Hsiao, QUE Corporation, USA, 1999.
   

  * Complete Idiot's Guide to Linux Second Edition, Manuel Alberto Ricart,
    QUE Corporation, USA, 1999.
   

  * Lions' Commentary on UNIX 6th Edition with Source Code, John Lions,
    Peer-to-Peer Communications Incorporated, USA, 1996.
   

  * The Linux System Administrators' Guide Version 0.6.1, Lars Wirzenius,
    liw@iki.fi, Finland, 1998.
   

  * SAMS Teach Yourself Shell Programming in 24 Hours, Sriranga
    Veerararaghavan, SAMS Publishing, USA, 1999.
   

  * 433-252 Software Development: Principles and Tools, Zoltan Somogyi, Les
    Kitchen, The University of Melbourne, Department of Computer Science and
    Software Engineering, Australia, 2002.
   

  * The Advanced Linux Pocketbook, Ashton Mills, ashtonmills@bigpond.com, ACP
    Publishing Pty Ltd, Australia, 2001.
   

  * http://www.pathname.com/fhs
   

  * http://www.atnf.csiro.au/people/rgooch/linux/docs/devfs.html
   

  * http://freeos.com/articles/3102/
   

  * http://freeos.com/articles/2879/
   

  * http://www.linuxjournal.com/article.php?sid=1104
   

  * http://www.mlinux.org/projects/present/filesys/slide01.html
   

  * http://www.mil.ufl.edu/linuxhelp/linuxfilesystem.pdf
   

  * http://www.nsa.gov/selinux/doc/slinux/node57.html
   

  * http://www.linuxnow.com/tutorial/fs/fs.html
   

  * http://info.cqu.edu.au/courses/aut2001/85321/resources/study_guide/
    chapter_4
   

  * http://lwn.net/2001/features/ols/pdf/pdf/devfs.pdf
   

  * /usr/src/linux/Documentation/filesystems/proc.txt, Terrehon Bowden <
    terrehon@pacbell.net>, Bodo Bauer <bb@ricochet.net>, Jorge Nerin <
    comandante@zaralinux.com>
   

  * /usr/share/doc/FAQ/Linux-FAQ/index.html, ftp://rtfm.mit.edu/pub/
    usenet-by-hierarchy/comp/os/linux/misc/, David Merrill, david -AT-
    lupercalia.net, Robert Kiesling, rkiesling@mainmatter.com, Linux
    Frequently Asked Questions with Answers, 2001-12-04.
   

  * /usr/share/doc/sysvinit/README.runlevels.gz
   

  * /usr/src/linux/Documentation/initrd.txt, Werner Almesberger <
    werner.almesberger@epfl.ch> and Hans Lermen <lermen@fgan.de>, 2000.
   

  * http://www.opussoftware.com/tutorial/TutMakefile.htm
   

  * http://www.cc.gatech.edu/people/home/oxblood/Linux_Doc.txt
   

  * http://users.erols.com/mmmcd/lilo/boot_sequence.html
   

  * hints.linuxfromscratch.org/hints/grub-howto.txt
   

  * http://www.fifi.org/cgi-bin/man2html?initrd+4
   

  * http://www.linuxsa.org.au/meetings/1997-06/fsstnd/fsstnd.html
   

  * http://public.csusm.edu/public/guests/history/netinfo/arpa.html
   

  * http://whatis.techtarget.com/definition/0,,sid9_gci214635,00.html
   

  * http://whatis.techtarget.com/definition/0,,sid9_gci213627,00.html
   

  * http://www.darpa.mil/
   

  * http://hostingworks.com/support/dict.phtml?foldoc=
    Defense%2BAdvanced%2BResearch%2BProjects%2BAgency
   

  * http://www.linuxsa.org.au/meetings/1997-06/fsstnd/fsstnd.html
   

  * http://compnetworking.about.com/library/glossary/bldef-dns.htm
   

  * http://www.scala.com/definition/graphical-user-interface.html
   

  * http://hostingworks.com/support/dict.phtml?foldoc=
    Graphical+User+Interface
   

  * http://www.mostang.com/sane/intro.html
   

-----------------------------------------------------------------------------
Appendix C. About the Author

  Binh Nguyen was born, 26 March 1983, Melbourne, Victoria. He studied at St
Josephs Marist Brothers College, North Fitzroy until receiving a scholarship
to St Kevin's College, Toorak in 1998.

  He is currently a university undergraduate studying computer science and
physics at the University of Melbourne. His main interests in each area are
in Operating Systems and Quantum Mechanics respectively.

  His background is strongly biased towards science and mathematics.
Nonetheless, he does have an appreciation for the arts, humanities and sport.
A reasonably proficient musician (flute), he is currently pondering whether
he should complete his musical studies to obtain a diploma so that he can
teach. In high school, he was a member of the athletics, basketball,
football, cricket and swimming squads. He speaks English predominately but is
also able to communicate in Vietnamese and French. When younger he also
possessed the ability to communicate in Chinese and Italian.

  Although brought up as a Buddhist and studying at Catholic/Christian
schools all his life as well as studying scripture during his final year of
high school he considers himself an atheist.

  At this moment in time, he works part-time as a (commercial) researcher/
developer on Linux related projects with his current focus being on software
distribution mechanisms.

  Two of his technical documents have been incorporated into the Linux
Documentation Project ("Linux Dictionary" and "Linux Filesystem Hierarchy",
[www.tldp.org/guides.html]   www.tldp.org/guides.html). Furthermore, they are
being used as reference books in at least ten universities around the world
(University of Southern Queensland (Australia), Universidad Michoacana
(Mexico), Hong Kong Polytechnic University (Hong Kong), Universidade de Sao
Paolo (Brazil), University of Southern California (United States of America),
University of Wales Swansea (United Kingdom), University of Ulster (Ireland),
Universität Duisburg-Essen (Germany), Universidad Rey Juan Carlos (Spain),
Insituto Superior Miguel Torga (Portugal), and Universiti Sains Malaysia
(Malaysia)). As well as this, he is also a Development Lead and Project
Administrator of the "Computer Dictionary Project" [http://
computerdictionary.tsf.org.za/dictionary/index.html]   http://
computerdictionary.tsf.org.za/dictionary/index.html which is being supported
by the Shuttleworth Foundation.

  He has published articles at linux.com, linmagau.org, desktoplinux.com,
newsforge.com, linuxtoday.com, linux.org, pclinuxonline.com, tuxreports.com,
etc.... and has a keen interest in the latest innovations in science and
technology.

  The author's homepage is at, [http://geocities.com/linuxfilesystem/]  
http://geocities.com/linuxfilesystem/
-----------------------------------------------------------------------------

Appendix D. Contributors

  The author would like to thank a group of members (who wish to remain
anonymous) from MLUG [http://www.mlug.org.au] http://www.mlug.org.au for
having the time and patience to help proof read this document before going to
publication.

  * Peter Yellman.
   

  * Clyde Forrester.
   

  * Geoff Farrell.
   

  * Nick Spence.
   

  * Christopher Priest.
   

-----------------------------------------------------------------------------
Appendix E. Disclaimer

  No liability for the contents of this document can be accepted. Use the
concepts, examples and other content at your own risk. As this is a new
edition of this document, there may be errors and inaccuracies that may of
course be damaging to your system. Proceed with caution, and although this is
highly unlikely, the author does not and can not take any responsibility for
any damage to your system that may occur as a direct or indirect result of
information that is contained within this document.

  Naming of particular products or brands should not be seen as endorsements.
You are strongly recommended to make a backup of your system before major
installation and adhere to the practice of backing up at regular intervals.
-----------------------------------------------------------------------------

Appendix F. Donations

  If you would like to make a donations towards this project please use
Paypal, [https://www.paypal.com] https://www.paypal.com.
-----------------------------------------------------------------------------

Appendix G. Feedback

  Further revisions of this document will be dependent upon user response.
Any feedback on the content of this document is welcome. Every attempt has
been made to ensure that the instructions and information herein are accurate
and reliable. Send comments, corrections, suggestions and questions to the
author Binh Nguyen, linuxfilesystem(at)yahoo(dot)com(dot)au with the subject
heading of LHFS. There is however, no guarantee of response.

  All trademarks and copyrights are the property of their owners, unless
otherwise indicated. Use of a term in this document should not be regarded as
affecting the validity of any trademark or service mark.

  The author would appreciate and consider it courteous, notification of any
and all modifications, translations, and printed versions.
-----------------------------------------------------------------------------

Appendix H. GNU Free Documentation License

Version 1.2, November 2002

   
    Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple
    Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy
    and distribute verbatim copies of this license document, but changing it
    is not allowed.
   
-----------------------------------------------------------------------------
H.1. PREAMBLE

The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to assure
everyone the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially. Secondarily, this
License preserves for the author and publisher a way to get credit for their
work, while not being considered responsible for modifications made by
others.

This License is a kind of "copyleft", which means that derivative works of
the document must themselves be free in the same sense. It complements the
GNU General Public License, which is a copyleft license designed for free
software.

We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free program
should come with manuals providing the same freedoms that the software does.
But this License is not limited to software manuals; it can be used for any
textual work, regardless of subject matter or whether it is published as a
printed book. We recommend this License principally for works whose purpose
is instruction or reference.
-----------------------------------------------------------------------------

H.2. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be distributed
under the terms of this License. Such a notice grants a world-wide,
royalty-free license, unlimited in duration, to use that work under the
conditions stated herein. The "Document", below, refers to any such manual or
work. Any member of the public is a licensee, and is addressed as "you". You
accept the license if you copy, modify or distribute the work in a way
requiring permission under copyright law.

A "Modified Version" of the Document means any work containing the Document
or a portion of it, either copied verbatim, or with modifications and/or
translated into another language.

A "Secondary Section" is a named appendix or a front-matter section of the
Document that deals exclusively with the relationship of the publishers or
authors of the Document to the Document's overall subject (or to related
matters) and contains nothing that could fall directly within that overall
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Secondary Section may not explain any mathematics.) The relationship could be
a matter of historical connection with the subject or with related matters,
or of legal, commercial, philosophical, ethical or political position
regarding them.

The "Invariant Sections" are certain Secondary Sections whose titles are
designated, as being those of Invariant Sections, in the notice that says
that the Document is released under this License. If a section does not fit
the above definition of Secondary then it is not allowed to be designated as
Invariant. The Document may contain zero Invariant Sections. If the Document
does not identify any Invariant Sections then there are none.

The "Cover Texts" are certain short passages of text that are listed, as
Front-Cover Texts or Back-Cover Texts, in the notice that says that the
Document is released under this License. A Front-Cover Text may be at most 5
words, and a Back-Cover Text may be at most 25 words.

A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the general
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been arranged to thwart or discourage subsequent modification by readers is
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Examples of suitable formats for Transparent copies include plain ASCII
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PDF designed for human modification. Examples of transparent image formats
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be read and edited only by proprietary word processors, SGML or XML for which
the DTD and/or processing tools are not generally available, and the
machine-generated HTML, PostScript or PDF produced by some word processors
for output purposes only.

The "Title Page" means, for a printed book, the title page itself, plus such
following pages as are needed to hold, legibly, the material this License
requires to appear in the title page. For works in formats which do not have
any title page as such, "Title Page" means the text near the most prominent
appearance of the work's title, preceding the beginning of the body of the
text.

A section "Entitled XYZ" means a named subunit of the Document whose title
either is precisely XYZ or contains XYZ in parentheses following text that
translates XYZ in another language. (Here XYZ stands for a specific section
name mentioned below, such as "Acknowledgements", "Dedications",
"Endorsements", or "History".) To "Preserve the Title" of such a section when
you modify the Document means that it remains a section "Entitled XYZ"
according to this definition.

The Document may include Warranty Disclaimers next to the notice which states
that this License applies to the Document. These Warranty Disclaimers are
considered to be included by reference in this License, but only as regards
disclaiming warranties: any other implication that these Warranty Disclaimers
may have is void and has no effect on the meaning of this License.
-----------------------------------------------------------------------------

H.3. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially
or noncommercially, provided that this License, the copyright notices, and
the license notice saying this License applies to the Document are reproduced
in all copies, and that you add no other conditions whatsoever to those of
this License. You may not use technical measures to obstruct or control the
reading or further copying of the copies you make or distribute. However, you
may accept compensation in exchange for copies. If you distribute a large
enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may
publicly display copies.
-----------------------------------------------------------------------------

H.4. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed
covers) of the Document, numbering more than 100, and the Document's license
notice requires Cover Texts, you must enclose the copies in covers that
carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the
front cover, and Back-Cover Texts on the back cover. Both covers must also
clearly and legibly identify you as the publisher of these copies. The front
cover must present the full title with all words of the title equally
prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the
title of the Document and satisfy these conditions, can be treated as
verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you
should put the first ones listed (as many as fit reasonably) on the actual
cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more
than 100, you must either include a machine-readable Transparent copy along
with each Opaque copy, or state in or with each Opaque copy a
computer-network location from which the general network-using public has
access to download using public-standard network protocols a complete
Transparent copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent
copy will remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or through
your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give them
a chance to provide you with an updated version of the Document.
-----------------------------------------------------------------------------

H.5. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the
conditions of sections 2 and 3 above, provided that you release the Modified
Version under precisely this License, with the Modified Version filling the
role of the Document, thus licensing distribution and modification of the
Modified Version to whoever possesses a copy of it. In addition, you must do
these things in the Modified Version:

 A. Use in the Title Page (and on the covers, if any) a title distinct from
    that of the Document, and from those of previous versions (which should,
    if there were any, be listed in the History section of the Document). You
    may use the same title as a previous version if the original publisher of
    that version gives permission.
   
 B. List on the Title Page, as authors, one or more persons or entities
    responsible for authorship of the modifications in the Modified Version,
    together with at least five of the principal authors of the Document (all
    of its principal authors, if it has fewer than five), unless they release
    you from this requirement.
   
 C. State on the Title page the name of the publisher of the Modified
    Version, as the publisher.
   
 D. Preserve all the copyright notices of the Document.
   
 E. Add an appropriate copyright notice for your modifications adjacent to
    the other copyright notices.
   
 F. Include, immediately after the copyright notices, a license notice giving
    the public permission to use the Modified Version under the terms of this
    License, in the form shown in the Addendum below.
   
 G. Preserve in that license notice the full lists of Invariant Sections and
    required Cover Texts given in the Document's license notice.
   
 H. Include an unaltered copy of this License.
   
 I. Preserve the section Entitled "History", Preserve its Title, and add to
    it an item stating at least the title, year, new authors, and publisher
    of the Modified Version as given on the Title Page. If there is no
    section Entitled "History" in the Document, create one stating the title,
    year, authors, and publisher of the Document as given on its Title Page,
    then add an item describing the Modified Version as stated in the
    previous sentence.
   
 J. Preserve the network location, if any, given in the Document for public
    access to a Transparent copy of the Document, and likewise the network
    locations given in the Document for previous versions it was based on.
    These may be placed in the "History" section. You may omit a network
    location for a work that was published at least four years before the
    Document itself, or if the original publisher of the version it refers to
    gives permission.
   
 K. For any section Entitled "Acknowledgements" or "Dedications", Preserve
    the Title of the section, and preserve in the section all the substance
    and tone of each of the contributor acknowledgements and/or dedications
    given therein.
   
 L. Preserve all the Invariant Sections of the Document, unaltered in their
    text and in their titles. Section numbers or the equivalent are not
    considered part of the section titles.
   
 M. Delete any section Entitled "Endorsements". Such a section may not be
    included in the Modified Version.
   
 N. Do not retitle any existing section to be Entitled "Endorsements" or to
    conflict in title with any Invariant Section.
   
 O. Preserve any Warranty Disclaimers.
   

If the Modified Version includes new front-matter sections or appendices that
qualify as Secondary Sections and contain no material copied from the
Document, you may at your option designate some or all of these sections as
invariant. To do this, add their titles to the list of Invariant Sections in
the Modified Version's license notice. These titles must be distinct from any
other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing
but endorsements of your Modified Version by various parties--for example,
statements of peer review or that the text has been approved by an
organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list of
Cover Texts in the Modified Version. Only one passage of Front-Cover Text and
one of Back-Cover Text may be added by (or through arrangements made by) any
one entity. If the Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity you are
acting on behalf of, you may not add another; but you may replace the old
one, on explicit permission from the previous publisher that added the old
one.

The author(s) and publisher(s) of the Document do not by this License give
permission to use their names for publicity for or to assert or imply
endorsement of any Modified Version.
-----------------------------------------------------------------------------

H.6. COMBINING DOCUMENTS

You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified versions,
provided that you include in the combination all of the Invariant Sections of
all of the original documents, unmodified, and list them all as Invariant
Sections of your combined work in its license notice, and that you preserve
all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple
identical Invariant Sections may be replaced with a single copy. If there are
multiple Invariant Sections with the same name but different contents, make
the title of each such section unique by adding at the end of it, in
parentheses, the name of the original author or publisher of that section if
known, or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of the
combined work.

In the combination, you must combine any sections Entitled "History" in the
various original documents, forming one section Entitled "History"; likewise
combine any sections Entitled "Acknowledgements", and any sections Entitled
"Dedications". You must delete all sections Entitled "Endorsements".
-----------------------------------------------------------------------------

H.7. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in the
collection, provided that you follow the rules of this License for verbatim
copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it
individually under this License, provided you insert a copy of this License
into the extracted document, and follow this License in all other respects
regarding verbatim copying of that document.
-----------------------------------------------------------------------------

H.8. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and
independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright resulting from
the compilation is not used to limit the legal rights of the compilation's
users beyond what the individual works permit. When the Document is included
in an aggregate, this License does not apply to the other works in the
aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of
the Document, then if the Document is less than one half of the entire
aggregate, the Document's Cover Texts may be placed on covers that bracket
the Document within the aggregate, or the electronic equivalent of covers if
the Document is in electronic form. Otherwise they must appear on printed
covers that bracket the whole aggregate.
-----------------------------------------------------------------------------

H.9. TRANSLATION

Translation is considered a kind of modification, so you may distribute
translations of the Document under the terms of section 4. Replacing
Invariant Sections with translations requires special permission from their
copyright holders, but you may include translations of some or all Invariant
Sections in addition to the original versions of these Invariant Sections.
You may include a translation of this License, and all the license notices in
the Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions of
those notices and disclaimers. In case of a disagreement between the
translation and the original version of this License or a notice or
disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications",
or "History", the requirement (section 4) to Preserve its Title (section 1)
will typically require changing the actual title.
-----------------------------------------------------------------------------

H.10. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as
expressly provided for under this License. Any other attempt to copy, modify,
sublicense or distribute the Document is void, and will automatically
terminate your rights under this License. However, parties who have received
copies, or rights, from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
-----------------------------------------------------------------------------

H.11. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU
Free Documentation License from time to time. Such new versions will be
similar in spirit to the present version, but may differ in detail to address
new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the
Document specifies that a particular numbered version of this License "or any
later version" applies to it, you have the option of following the terms and
conditions either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may choose
any version ever published (not as a draft) by the Free Software Foundation.
-----------------------------------------------------------------------------

H.12. ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the
License in the document and put the following copyright and license notices
just after the title page:

   
      Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute
    and/or modify this document under the terms of the GNU Free Documentation
    License, Version 1.2 or any later version published by the Free Software
    Foundation; with no Invariant Sections, no Front-Cover Texts, and no
    Back-Cover Texts. A copy of the license is included in the section
    entitled "GNU Free Documentation License".
   
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

   
      with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
   
If you have Invariant Sections without Cover Texts, or some other combination
of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend
releasing these examples in parallel under your choice of free software
license, such as the GNU General Public License, to permit their use in free
software.

Notes

[1]  It requires several seconds of hard thinking on the users' behalf.      
     Furthermore sudo can be configured to only allow users to execute       
     certain commands. See the sudo(8), sudoers(5), and visudo(8) manual     
     pages.