Linux Filesystem Hierarchy
Version 0.65
Binh Nguyen
<dtbnguyen(at)gmail(dot)com>
Copyright 2003 Binh Nguyen
Trademarks are owned by their owners.
Permission is granted to copy, distribute and/or modify this document under the
terms of the GNU Free Documentation License, Version 1.2; with no Invariant
Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of
the license is included in the section entitled "GNU Free Documentation
License".
2004-07-30
Abstract
This document outlines the set of requirements and guidelines for file and
directory placement under the Linux operating system according to those of the
FSSTND v2.3 final (January 29, 2004) and also its actual implementation on an
arbitrary system. It is meant to be accessible to all members of the Linux
community, be distribution independent and is intended to discuss the impact of
the FSSTND and how it has managed to increase the efficiency of support
interoperability of applications, system administration tools, development
tools, and scripts as well as greater uniformity of documentation for these
systems.
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Table of Contents
Source_and_pre-formatted_versions_available
1._Linux_Filesystem_Hierarchy
1._Foreward
2._The_Root_Directory
3._/bin
4._/boot
5._/dev
6._/etc
7._/home
8._/initrd
9._/lib
10._/lost+found
11._/media
12._/mnt
12.1._Mounting_and_unmounting
13._/opt
14._/proc
15._/root
16._/sbin
17._/usr
18._/var
19._/srv
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
1._PREAMBLE
2._APPLICABILITY_AND_DEFINITIONS
3._VERBATIM_COPYING
4._COPYING_IN_QUANTITY
5._MODIFICATIONS
6._COMBINING_DOCUMENTS
7._COLLECTIONS_OF_DOCUMENTS
8._AGGREGATION_WITH_INDEPENDENT_WORKS
9._TRANSLATION
10._TERMINATION
11._FUTURE_REVISIONS_OF_THIS_LICENSE
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
The latest version of this document can be found at http://cvsview.tldp.org/
index.cgi/LDP/guide/docbook/Linux-Filesystem-Hierarchy/
Chapter 1. Linux Filesystem Hierarchy
Table of Contents
1._Foreward
2._The_Root_Directory
3._/bin
4._/boot
5._/dev
6._/etc
7._/home
8._/initrd
9._/lib
10._/lost+found
11._/media
12._/mnt
12.1._Mounting_and_unmounting
13._/opt
14._/proc
15._/root
16._/sbin
17._/usr
18._/var
19._/srv
20._/tmp
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 filesystemis 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 functionof 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 shouldbe, 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).
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.
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.
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.
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
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/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.
# $Id$
# 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:
# $Id$
#
# 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: # $Id$ # #
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/<subdir>, where
<subdir> 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/<subdir>.
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/<subdir>.
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.
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.
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.
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).
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
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.
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.
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.
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:\Program
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.
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.
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.
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)
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.
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)
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.
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).
-------------------------------------------------------------------------------
[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.
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
The author's homepage is at, http://dtbnguyen.googlepages.com/
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 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.
* Gareth Williams.
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.
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, dtbnguyen(at)gmail(dot)com with the subject heading of 'Linux
Filesystem'. 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
Table of Contents
1._PREAMBLE
2._APPLICABILITY_AND_DEFINITIONS
3._VERBATIM_COPYING
4._COPYING_IN_QUANTITY
5._MODIFICATIONS
6._COMBINING_DOCUMENTS
7._COLLECTIONS_OF_DOCUMENTS
8._AGGREGATION_WITH_INDEPENDENT_WORKS
9._TRANSLATION
10._TERMINATION
11._FUTURE_REVISIONS_OF_THIS_LICENSE
12._ADDENDUM:_How_to_use_this_License_for_your_documents
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.
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.
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
subject. (Thus, if the Document is in part a textbook of mathematics, a
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 public, that is
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or (for images composed of pixels) generic paint programs or (for drawings)
some widely available drawing editor, and that is suitable for input to text
formatters or for automatic translation to a variety of formats suitable for
input to text formatters. A copy made in an otherwise Transparent file format
whose markup, or absence of markup, has been arranged to thwart or discourage
subsequent modification by readers is not Transparent. An image format is not
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"Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain ASCII without
markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly
available DTD, and standard-conforming simple HTML, PostScript or PDF designed
for human modification. Examples of transparent image formats include PNG, XCF
and JPG. Opaque formats include proprietary formats that can 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.
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.
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.
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.
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".
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.
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.
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.
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.
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.
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.