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Filesystem Hierarchy Standard
LSB Workgroup, The Linux Foundation
Version 3.0
Copyright © 2015 The Linux Foundation
Copyright © 1994-2004 Daniel Quinlan
Copyright © 2001-2004 Paul 'Rusty' Russell
Copyright © 2003-2004 Christopher Yeoh
All trademarks and copyrights are owned by their owners, unless
specifically noted otherwise. Use of a term in this document
should not be regarded as affecting the validity of any
trademark or service mark.
Permission is granted to make and distribute verbatim copies of
this standard provided the copyright and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions
of this standard under the conditions for verbatim copying,
provided also that the title page is labeled as modified
including a reference to the original standard, provided that
information on retrieving the original standard is included,
and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to
this one.
Permission is granted to copy and distribute translations of
this standard into another language, under the above conditions
for modified versions, except that this permission notice may
be stated in a translation approved by the copyright holder.
March 19, 2015
Abstract
This standard consists of a set of requirements and guidelines
for file and directory placement under UNIX-like operating
systems. The guidelines are intended to support
interoperability of applications, system administration tools,
development tools, and scripts as well as greater uniformity of
documentation for these systems.
__________________________________________________________
Dedication
This release is dedicated to the memory of Christopher Yeoh, a
long-time friend and colleague, and one of the original editors
of the FHS. Without his dedication this work would not have
been possible.
Table of Contents
1. Introduction
1.1. Purpose
1.2. Conventions
2. The Filesystem
3. The Root Filesystem
3.1. Purpose
3.2. Requirements
3.3. Specific Options
3.4. /bin : Essential user command binaries (for use by
all users)
3.4.1. Purpose
3.4.2. Requirements
3.4.3. Specific Options
3.5. /boot : Static files of the boot loader
3.5.1. Purpose
3.5.2. Specific Options
3.6. /dev : Device files
3.6.1. Purpose
3.6.2. Specific Options
3.7. /etc : Host-specific system configuration
3.7.1. Purpose
3.7.2. Requirements
3.7.3. Specific Options
3.7.4. /etc/opt : Configuration files for /opt
3.7.5. /etc/X11 : Configuration for the X Window
System (optional)
3.7.6. /etc/sgml : Configuration files for SGML
(optional)
3.7.7. /etc/xml : Configuration files for XML
(optional)
3.8. /home : User home directories (optional)
3.8.1. Purpose
3.8.2. Requirements
3.8.3. Home Directory Specifications and Conventions
3.9. /lib : Essential shared libraries and kernel modules
3.9.1. Purpose
3.9.2. Requirements
3.9.3. Specific Options
3.10. /lib<qual> : Alternate format essential shared
libraries (optional)
3.10.1. Purpose
3.10.2. Requirements
3.11. /media : Mount point for removable media
3.11.1. Purpose
3.11.2. Specific Options
3.12. /mnt : Mount point for a temporarily mounted
filesystem
3.12.1. Purpose
3.13. /opt : Add-on application software packages
3.13.1. Purpose
3.13.2. Requirements
3.14. /root : Home directory for the root user (optional)
3.14.1. Purpose
3.15. /run : Run-time variable data
3.15.1. Purpose
3.15.2. Requirements
3.16. /sbin : System binaries
3.16.1. Purpose
3.16.2. Requirements
3.16.3. Specific Options
3.17. /srv : Data for services provided by this system
3.17.1. Purpose
3.18. /tmp : Temporary files
3.18.1. Purpose
4. The /usr Hierarchy
4.1. Purpose
4.2. Requirements
4.3. Specific Options
4.4. /usr/bin : Most user commands
4.4.1. Purpose
4.4.2. Requirements
4.4.3. Specific Options
4.5. /usr/include : Directory for standard include files.
4.5.1. Purpose
4.5.2. Specific Options
4.6. /usr/lib : Libraries for programming and packages
4.6.1. Purpose
4.6.2. Specific Options
4.7. /usr/libexec : Binaries run by other programs
(optional)
4.7.1. Purpose
4.8. /usr/lib<qual> : Alternate format libraries
(optional)
4.8.1. Purpose
4.9. /usr/local : Local hierarchy
4.9.1. Purpose
4.9.2. Requirements
4.9.3. Specific Options
4.9.4. /usr/local/share : Local
architecture-independent hierarchy
4.10. /usr/sbin : Non-essential standard system binaries
4.10.1. Purpose
4.10.2. Requirements
4.11. /usr/share : Architecture-independent data
4.11.1. Purpose
4.11.2. Requirements
4.11.3. Specific Options
4.11.4. /usr/share/color : Color management
information (optional)
4.11.5. /usr/share/dict : Word lists (optional)
4.11.6. /usr/share/man : Manual pages
4.11.7. /usr/share/misc : Miscellaneous
architecture-independent data
4.11.8. /usr/share/ppd : Printer definitions
(optional)
4.11.9. /usr/share/sgml : SGML data (optional)
4.11.10. /usr/share/xml : XML data (optional)
4.12. /usr/src : Source code (optional)
4.12.1. Purpose
5. The /var Hierarchy
5.1. Purpose
5.2. Requirements
5.3. Specific Options
5.4. /var/account : Process accounting logs (optional)
5.4.1. Purpose
5.5. /var/cache : Application cache data
5.5.1. Purpose
5.5.2. Specific Options
5.5.3. /var/cache/fonts : Locally-generated fonts
(optional)
5.5.4. /var/cache/man : Locally-formatted manual
pages (optional)
5.6. /var/crash : System crash dumps (optional)
5.6.1. Purpose
5.7. /var/games : Variable game data (optional)
5.7.1. Purpose
5.8. /var/lib : Variable state information
5.8.1. Purpose
5.8.2. Requirements
5.8.3. Specific Options
5.8.4. /var/lib/<editor> : Editor backup files and
state (optional)
5.8.5. /var/lib/color : Color management information
(optional)
5.8.6. /var/lib/hwclock : State directory for
hwclock (optional)
5.8.7. /var/lib/misc : Miscellaneous variable data
5.9. /var/lock : Lock files
5.9.1. Purpose
5.10. /var/log : Log files and directories
5.10.1. Purpose
5.10.2. Specific Options
5.11. /var/mail : User mailbox files (optional)
5.11.1. Purpose
5.12. /var/opt : Variable data for /opt
5.12.1. Purpose
5.13. /var/run : Run-time variable data
5.13.1. Purpose
5.13.2. Requirements
5.14. /var/spool : Application spool data
5.14.1. Purpose
5.14.2. Specific Options
5.14.3. /var/spool/lpd : Line-printer daemon print
queues (optional)
5.14.4. /var/spool/rwho : Rwhod files (optional)
5.15. /var/tmp : Temporary files preserved between system
reboots
5.15.1. Purpose
5.16. /var/yp : Network Information Service (NIS) database
files (optional)
5.16.1. Purpose
6. Operating System Specific Annex
6.1. Linux
6.1.1. / : Root directory
6.1.2. /bin : Essential user command binaries (for
use by all users)
6.1.3. /dev : Devices and special files
6.1.4. /etc : Host-specific system configuration
6.1.5. /proc : Kernel and process information
virtual filesystem
6.1.6. /sbin : Essential system binaries
6.1.7. /sys : Kernel and system information virtual
filesystem
6.1.8. /usr/include : Header files included by C
programs
6.1.9. /usr/src : Source code
6.1.10. /var/spool/cron : cron and at jobs
7. Appendix
7.1. The FHS mailing list
7.2. Background of the FHS
7.3. General Guidelines
7.4. Scope
7.5. Acknowledgments
7.6. Contributors
Chapter 1. Introduction
Table of Contents
1.1. Purpose
1.2. Conventions
1.1. Purpose
This standard enables:
* Software to predict the location of installed files and
directories, and
* Users to predict the location of installed files and
directories.
We do this by:
* Specifying guiding principles for each area of the
filesystem,
* Specifying the minimum files and directories required,
* Enumerating exceptions to the principles, and
* Enumerating specific cases where there has been historical
conflict.
The FHS document is used by:
* Independent software suppliers to create applications which
are FHS compliant, and work with distributions which are
FHS compliant,
* OS creators to provide systems which are FHS compliant, and
* Users to understand and maintain the FHS compliance of a
system.
The FHS document has a limited scope:
* Local placement of local files is a local issue, so FHS
does not attempt to usurp system administrators.
* FHS addresses issues where file placements need to be
coordinated between multiple parties such as local sites,
distributions, applications, documentation, etc.
1.2. Conventions
We recommend that you read a typeset version of this document
rather than the plain text version. In the typeset version, the
names of files and directories are displayed in a
constant-width font.
Components of filenames that vary are represented by a
description of the contents enclosed in "<" and ">" characters,
<thus>. Electronic mail addresses are also enclosed in "<" and
">" but are shown in the usual typeface.
Optional components of filenames are enclosed in "[" and "]"
characters and may be combined with the "<" and ">" convention.
For example, if a filename is allowed to occur either with or
without an extension, it might be represented by
<filename>[.<extension>].
Variable substrings of directory names and filenames are
indicated by "*".
The sections of the text marked as Rationale are explanatory
and are non-normative.
Chapter 2. The Filesystem
This standard assumes that the operating system underlying an
FHS-compliant file system supports the same basic security
features found in most UNIX filesystems.
It is possible to define two independent distinctions among
files: shareable vs. unshareable and variable vs. static. In
general, files that differ in either of these respects should
be located in different directories. This makes it easy to
store files with different usage characteristics on different
filesystems.
"Shareable" files are 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 files that are not static.
Rationale
Shareable files can be stored on one host and used on several
others. Typically, however, not all files in the filesystem
hierarchy are shareable and so each system has local storage
containing at least its unshareable files. It is convenient if
all the files a system requires that are stored on a foreign
host can be made available by mounting one or a few directories
from the foreign host.
Static and variable files should be segregated because static
files, unlike variable files, can be stored on read-only media
and do not need to be backed up on the same schedule as
variable files.
Historical UNIX-like filesystem hierarchies contained both
static and variable files under both /usr and /etc. In order to
realize the advantages mentioned above, the /var hierarchy was
created and all variable files were transferred from /usr to
/var. Consequently /usr can now be mounted read-only (if it is
a separate filesystem). Variable files have been transferred
from /etc to /var over a longer period as technology has
permitted.
Here is an example of a FHS-compliant system. (Other
FHS-compliant layouts are possible.)
shareable unshareable
static /usr /etc
/opt /boot
variable /var/mail /var/run
/var/spool/news /var/lock
Chapter 3. The Root Filesystem
Table of Contents
3.1. Purpose
3.2. Requirements
3.3. Specific Options
3.4. /bin : Essential user command binaries (for use by all
users)
3.4.1. Purpose
3.4.2. Requirements
3.4.3. Specific Options
3.5. /boot : Static files of the boot loader
3.5.1. Purpose
3.5.2. Specific Options
3.6. /dev : Device files
3.6.1. Purpose
3.6.2. Specific Options
3.7. /etc : Host-specific system configuration
3.7.1. Purpose
3.7.2. Requirements
3.7.3. Specific Options
3.7.4. /etc/opt : Configuration files for /opt
3.7.5. /etc/X11 : Configuration for the X Window System
(optional)
3.7.6. /etc/sgml : Configuration files for SGML (optional)
3.7.7. /etc/xml : Configuration files for XML (optional)
3.8. /home : User home directories (optional)
3.8.1. Purpose
3.8.2. Requirements
3.8.3. Home Directory Specifications and Conventions
3.9. /lib : Essential shared libraries and kernel modules
3.9.1. Purpose
3.9.2. Requirements
3.9.3. Specific Options
3.10. /lib<qual> : Alternate format essential shared libraries
(optional)
3.10.1. Purpose
3.10.2. Requirements
3.11. /media : Mount point for removable media
3.11.1. Purpose
3.11.2. Specific Options
3.12. /mnt : Mount point for a temporarily mounted filesystem
3.12.1. Purpose
3.13. /opt : Add-on application software packages
3.13.1. Purpose
3.13.2. Requirements
3.14. /root : Home directory for the root user (optional)
3.14.1. Purpose
3.15. /run : Run-time variable data
3.15.1. Purpose
3.15.2. Requirements
3.16. /sbin : System binaries
3.16.1. Purpose
3.16.2. Requirements
3.16.3. Specific Options
3.17. /srv : Data for services provided by this system
3.17.1. Purpose
3.18. /tmp : Temporary files
3.18.1. Purpose
3.1. Purpose
The contents of the root filesystem must be adequate to boot,
restore, recover, and/or repair the system.
* To boot a system, enough software and data must be present
on the root partition to mount other filesystems. This
includes utilities, configuration, boot loader information,
and other essential start-up data. /usr, /opt, and /var are
designed such that they may be located on other partitions
or filesystems.
* To enable recovery and/or repair of a system, those
utilities needed by an experienced maintainer to diagnose
and reconstruct a damaged system must be present on the
root filesystem.
* To restore a system, those utilities needed to restore from
system backups (on floppy, tape, etc.) must be present on
the root filesystem.
Rationale
The minimum requirements for the root filesystem should be as
small as reasonably possible, but no smaller. While many users
may not want the extra complexity of a partitioned system, the
option to keep the root small should be preserved for several
reasons:
* It is occasionally mounted from very small media.
* The root filesystem contains many system-specific
configuration files. Possible examples include a kernel
that is specific to the system, a specific hostname, etc.
This means that the root filesystem isn't always shareable
between networked systems. Keeping it small on servers in
networked systems minimizes the amount of lost space for
areas of unshareable files. It also allows workstations
with smaller local hard drives.
* While you may have the root filesystem on a large
partition, and may be able to fill it to your heart's
content, there will be people with smaller partitions. If
you have more files installed, you may find
incompatibilities with other systems using root filesystems
on smaller partitions. If you are a developer then you may
be turning your assumption into a problem for a large
number of users.
* Disk errors that corrupt data on the root filesystem are a
greater problem than errors on any other partition. A small
root filesystem is less prone to corruption as the result
of a system crash.
These considerations must be balanced against the need for a
minimally useful operating environment, for the sake of the
boot process as well as in failure recovery situations.
Applications must never create or require special files or
subdirectories in the root directory. Other locations in the
FHS hierarchy provide more than enough flexibility for any
package.
Rationale
There are several reasons why creating a new subdirectory of
the root filesystem is prohibited:
* It demands space on a root partition which the system
administrator may want kept small and simple for either
performance or security reasons.
* It evades whatever discipline the system administrator may
have set up for distributing standard file hierarchies
across mountable volumes.
Distributions should not create new directories in the root
hierarchy without extremely careful consideration of the
consequences including for application portability.
3.2. Requirements
The following directories, or symbolic links to directories,
are required in /.
Directory Description
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 removable media
mnt Mount point for mounting a filesystem temporarily
opt Add-on application software packages
run Data relevant to running processes
sbin Essential system binaries
srv Data for services provided by this system
tmp Temporary files
usr Secondary hierarchy
var Variable data
Each directory listed above is specified in detail in separate
subsections below. /usr and /var each has a complete section in
this document due to the complexity of those directories.
3.3. Specific Options
The following directories, or symbolic links to directories,
must be in /, if the corresponding subsystem is installed:
Directory Description
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 specified in detail in separate
subsections below.
3.4. /bin : Essential user command binaries (for use by all users)
3.4.1. Purpose
/bin contains commands that may be used by both the system
administrator and by users, but which are required when no
other filesystems are mounted (e.g. in single user mode). It
may also contain commands which are used indirectly by scripts.
^[1]
3.4.2. Requirements
There must be no subdirectories in /bin.
The following commands, or symbolic links to commands, are
required in /bin:
Command Description
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 POSIX compatible 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 the POSIX compatible shell command itself, it
must be a hard or symbolic link to the real shell command.
The [ and test commands must be placed together in either /bin
or /usr/bin.
Rationale
Various shells behave differently when called as sh, so as to
preserve POSIX compatibility while allowing changes or
extensions to POSIX when desired.
The requirement for the [ and test commands to be included as
binaries (even if implemented internally by the shell) is
shared with the POSIX.1-2008 standard.
3.4.3. Specific Options
The following programs, or symbolic links to programs, must be
in /bin if the corresponding subsystem is installed:
Command Description
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)
/bin/csh may be a symbolic link to /bin/tcsh or /usr/bin/tcsh.
Rationale
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.
3.5. /boot : Static files of the boot loader
3.5.1. Purpose
This directory contains everything required for the boot
process except configuration files not needed at boot time and
the map installer. Thus /boot stores data that is used before
the kernel begins executing user-mode programs. This may
include saved master boot sectors and sector map files.
Programs necessary to arrange for the boot loader to be able to
boot a file must be placed in /sbin. Configuration files for
boot loaders that are not required at boot time must be placed
in /etc.
3.5.2. Specific Options
The operating system kernel must be located in either / or
/boot.
Certain architectures may have other requirements for /boot
related to limitations or expectations specific to that
architecture. These requirements are not enumerated here;
distributions are allowed to add requirements as needed to
enable system startup on these architectures.
3.6. /dev : Device files
3.6.1. Purpose
The /dev directory is the location of special or device files.
3.6.2. Specific Options
If it is possible that devices in /dev will need to be manually
created, /dev must contain a command named MAKEDEV, which can
create devices as needed. It may also contain a MAKEDEV.local
for any local devices.
If required, MAKEDEV must have provisions for creating any
device that may be found on the system, not just those that a
particular distribution installs.
3.7. /etc : Host-specific system configuration
3.7.1. Purpose
The /etc hierarchy contains configuration files. A
"configuration file" is a local file used to control the
operation of a program; it must be static and cannot be an
executable binary. ^[2]
It is recommended that files be stored in subdirectories of
/etc rather than directly in /etc.
3.7.2. Requirements
No binaries may be located under /etc.
The following directories, or symbolic links to directories are
required in /etc:
Directory Description
opt Configuration for /opt
3.7.3. Specific Options
The following directories, or symbolic links to directories
must be in /etc, if the corresponding subsystem is installed:
Directory Description
X11 Configuration for the X Window system (optional)
sgml Configuration for SGML (optional)
xml Configuration for XML (optional)
The following files, or symbolic links to files, must be in
/etc if the corresponding subsystem is installed: ^[3]
File Description
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. ^[4]
3.7.4. /etc/opt : Configuration files for /opt
3.7.4.1. Purpose
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.
3.7.4.2. Requirements
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>.
Rationale
Refer to the rationale for /opt.
3.7.5. /etc/X11 : Configuration for the X Window System (optional)
3.7.5.1. Purpose
/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.
3.7.5.2. Specific Options
The following files, or symbolic links to files, must be in
/etc/X11 if the corresponding subsystem is installed:
File Description
xorg.conf The configuration file for X.org versions 7 and later
(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. ^[5]
3.7.6. /etc/sgml : Configuration files for SGML (optional)
3.7.6.1. Purpose
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.
3.7.7. /etc/xml : Configuration files for XML (optional)
3.7.7.1. Purpose
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.
3.8. /home : User home directories (optional)
3.8.1. Purpose
/home is a fairly standard concept, but it is clearly a
site-specific filesystem. ^[6] The setup will differ from host
to host. Therefore, no program should assume any specific
location for a home directory, rather it should query for it.
^[7]
3.8.2. Requirements
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. ^[8]
3.8.3. Home Directory Specifications and Conventions
A number of efforts have been made in the past to standardize
the layout of home directories, including the XDG Base
Directories specification ^[9] and the GLib conventions on user
directory contents. ^[10] Additional efforts in this direction
are possible in the future. To accomodate software which makes
use of these specifications and conventions, distributions may
create directory hierarchies which follow the specifications
and conventions. Those directory hierarchies may be located
underneath home directories.
3.9. /lib : Essential shared libraries and kernel modules
3.9.1. Purpose
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. ^[11]
3.9.2. Requirements
At least one of each of the following filename patterns are
required (they may be files, or symbolic links):
File Description
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. ^[12]
3.9.3. Specific Options
The following directories, or symbolic links to directories,
must be in /lib, if the corresponding subsystem is installed:
Directory Description
modules Loadable kernel modules (optional)
3.10. /lib<qual> : Alternate format essential shared libraries
(optional)
3.10.1. Purpose
There may be one or more variants of the /lib directory on
systems which support more than one binary format requiring
separate libraries. ^[13]
3.10.2. Requirements
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. ^[14]
3.11. /media : Mount point for removable media
3.11.1. Purpose
This directory contains subdirectories which are used as mount
points for removable media such as floppy disks, cdroms and zip
disks.
Rationale
Historically there have been a number of other different places
used to mount removable media such as /cdrom, /mnt or
/mnt/cdrom. Placing the mount points for all removable 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.
3.11.2. Specific Options
The following directories, or symbolic links to directories,
must be in /media, if the corresponding subsystem is installed:
Directory Description
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. ^[15]
3.12. /mnt : Mount point for a temporarily mounted filesystem
3.12.1. Purpose
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.
3.13. /opt : Add-on application software packages
3.13.1. Purpose
/opt is reserved for the installation of add-on application
software packages.
A package to be installed in /opt must locate its static files
in a separate /opt/<package> or /opt/<provider> directory tree,
where <package> is a name that describes the software package
and <provider> is the provider's LANANA registered name.
3.13.2. Requirements
Directory Description
<package> Static package objects
<provider> LANANA registered provider name
The directories /opt/bin, /opt/doc, /opt/include, /opt/info,
/opt/lib, and /opt/man 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 local system administrator, but must
function normally in the absence of these reserved directories.
Programs to be invoked by users must be located in the
directory /opt/<package>/bin or under the /opt/<provider>
hierarchy. If the package includes UNIX manual pages, they must
be located in /opt/<package>/share/man or under the
/opt/<provider> hierarchy, and the same substructure as
/usr/share/man must be used.
Package files that are variable (change in normal operation)
must be installed in /var/opt. See the section on /var/opt for
more information.
Host-specific configuration files must be installed in
/etc/opt. See the section on /etc for more information.
No other package files may 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 must
be placed in /var/lock and devices must be located in /dev.
Distributions may install and otherwise manage software in /opt
under an appropriately registered subdirectory.
Rationale
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), provides for an /opt structure very
similar to the one defined here.
The Intel Binary Compatibility Standard v. 2 (iBCS2) also
provides a similar structure for /opt.
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.
3.14. /root : Home directory for the root user (optional)
3.14.1. Purpose
The root account's home directory may be determined by
developer or local preference, but this is the recommended
default location. ^[16]
3.15. /run : Run-time variable data
3.15.1. Purpose
This directory contains system information data describing the
system since it was booted. Files under this directory must be
cleared (removed or truncated as appropriate) at the beginning
of the boot process.
The purposes of this directory were once served by /var/run. In
general, programs may continue to use /var/run to fulfill the
requirements set out for /run for the purposes of backwards
compatibility. Programs which have migrated to use /run should
cease their usage of /var/run, except as noted in the section
on /var/run.
Programs may have a subdirectory of /run; this is encouraged
for programs that use more than one run-time file. Users may
also have a subdirectory of /run, although care must be taken
to appropriately limit access rights to prevent unauthorized
use of /run itself and other subdirectories. ^[17]
3.15.2. Requirements
Process identifier (PID) files, which were originally placed in
/etc, must be placed in /run. The naming convention for PID
files is <program-name>.pid. For example, the crond PID file is
named /run/crond.pid.
The internal format of PID files remains unchanged. The file
must consist of the process identifier in ASCII-encoded
decimal, followed by a newline character. For example, if crond
was process number 25, /run/crond.pid would contain three
characters: two, five, and newline.
Programs that read PID files should be somewhat flexible in
what they accept; i.e., they should ignore extra whitespace,
leading zeroes, absence of the trailing newline, or additional
lines in the PID file. Programs that create PID files should
use the simple specification located in the above paragraph.
System programs that maintain transient UNIX-domain sockets
must place them in this directory or an appropriate
subdirectory as outlined above.
3.16. /sbin : System binaries
3.16.1. Purpose
Utilities used for system administration (and other root-only
commands) are stored in /sbin, /usr/sbin, and /usr/local/sbin.
/sbin contains binaries essential for booting, restoring,
recovering, and/or repairing the system in addition to the
binaries in /bin. ^[18] Programs executed after /usr is known
to be mounted (when there are no problems) are generally placed
into /usr/sbin. Locally-installed system administration
programs should be placed into /usr/local/sbin. ^[19]
3.16.2. Requirements
There must be no subdirectories in /sbin.
The following commands, or symbolic links to commands, are
required in /sbin:
Command Description
shutdown Command to bring the system down.
3.16.3. Specific Options
The following files, or symbolic links to files, must be in
/sbin if the corresponding subsystem is installed:
Command Description
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)
3.17. /srv : Data for services provided by this system
3.17.1. Purpose
/srv contains site-specific data which is served by this
system.
Rationale
This main purpose of specifying this is so that users may find
the location of the data files for a 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. If the directory
and file structure of the data is not exposed to consumers, it
should go in /var/lib.
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. ^[20]
3.18. /tmp : Temporary files
3.18.1. Purpose
The /tmp directory must be made available for programs that
require temporary files.
Programs must not assume that any files or directories in /tmp
are preserved between invocations of the program.
Rationale
IEEE standard POSIX.1-2008 lists requirements similar to the
above section.
Although data stored in /tmp may be deleted in a site-specific
manner, it is recommended that files and directories located in
/tmp be deleted whenever the system is booted.
FHS added this recommendation on the basis of historical
precedent and common practice, but did not make it a
requirement because system administration is not within the
scope of this standard.
__________________________________________________________
^[1] Command binaries that are not essential enough to place
into /bin must be placed in /usr/bin, instead. Items that are
required only by non-root users (the X Window System, chsh,
etc.) are generally not essential enough to be placed into the
root partition.
^[2] To be clear, /etc may contain executable scripts, such as
the command scripts commonly called by init to start and shut
down the system and start daemon processes. "Executable binary"
in this context refers to direct machine code or pseudocode not
in a human-readable format, such as native ELF executables.
^[3] Systems that use the shadow password suite will have
additional configuration files in /etc (/etc/shadow and others)
and programs in /usr/sbin (useradd, usermod, and others).
^[4] On some Linux systems, this may be a symbolic link to
/proc/mounts, in which case this exception is not required.
^[5] /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.
^[6] 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 user home directories. Non-login accounts created
for administrative purposes often have their home directories
elsewhere.
On smaller systems, each user's home directory is typically
implemented as a subdirectory directly under /home, for example
/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.
^[7] To find a user's home directory, use a library function
such as getpwent, getpwent_r of fgetpwent rather than relying
on /etc/passwd because user information may be stored remotely
using systems such as NIS.
^[8] 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 consent.
^[9] Found at
http://standards.freedesktop.org/basedir-spec/basedir-spec-late
st.html and
http://www.freedesktop.org/wiki/Software/xdg-user-dirs.
^[10] A description of GLib's conventions can be found in the
documentation for GUserDirectory, at
http://developer.gnome.org/glib/unstable/glib-Miscellaneous-Uti
lity-Functions.html#GUserDirectory.
^[11] 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.
^[12] The usual placement of this binary is /usr/bin/cpp.
^[13] 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.
^[14] /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).
^[15] A compliant distribution with two CDROM drives might have
/media/cdrom0 and /media/cdrom1 with /media/cdrom a symlink to
either of these.
^[16] 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 cannot 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.
^[17] /run should not be writable for unprivileged users; it is
a major security problem if any user can write in this
directory. User-specific subdirectories should be writable only
by each directory's owner.
^[18] Originally, /sbin binaries were kept in /etc.
^[19] 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.
^[20] This is particularly important as these areas will often
contain both files initially installed by the distributor, and
those added by the administrator.
Chapter 4. The /usr Hierarchy
Table of Contents
4.1. Purpose
4.2. Requirements
4.3. Specific Options
4.4. /usr/bin : Most user commands
4.4.1. Purpose
4.4.2. Requirements
4.4.3. Specific Options
4.5. /usr/include : Directory for standard include files.
4.5.1. Purpose
4.5.2. Specific Options
4.6. /usr/lib : Libraries for programming and packages
4.6.1. Purpose
4.6.2. Specific Options
4.7. /usr/libexec : Binaries run by other programs (optional)
4.7.1. Purpose
4.8. /usr/lib<qual> : Alternate format libraries (optional)
4.8.1. Purpose
4.9. /usr/local : Local hierarchy
4.9.1. Purpose
4.9.2. Requirements
4.9.3. Specific Options
4.9.4. /usr/local/share : Local architecture-independent
hierarchy
4.10. /usr/sbin : Non-essential standard system binaries
4.10.1. Purpose
4.10.2. Requirements
4.11. /usr/share : Architecture-independent data
4.11.1. Purpose
4.11.2. Requirements
4.11.3. Specific Options
4.11.4. /usr/share/color : Color management information
(optional)
4.11.5. /usr/share/dict : Word lists (optional)
4.11.6. /usr/share/man : Manual pages
4.11.7. /usr/share/misc : Miscellaneous
architecture-independent data
4.11.8. /usr/share/ppd : Printer definitions (optional)
4.11.9. /usr/share/sgml : SGML data (optional)
4.11.10. /usr/share/xml : XML data (optional)
4.12. /usr/src : Source code (optional)
4.12.1. Purpose
4.1. Purpose
/usr is the second major section of the filesystem. /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.
4.2. Requirements
The following directories, or symbolic links to directories,
are required in /usr.
Directory Description
bin Most user commands
lib Libraries
local Local hierarchy (empty after main installation)
sbin Non-vital system binaries
share Architecture-independent data
4.3. Specific Options
Directory Description
games Games and educational binaries (optional)
include Header files included by C programs
libexec Binaries run by other programs (optional)
lib<qual> Alternate Format Libraries (optional)
src Source code (optional)
An exception is made for the X Window System because of
considerable precedent and widely-accepted practice.
The following symbolic links to directories may be present.
This possibility is based on the need to preserve compatibility
with older systems until all distribution can be assumed to use
the /var hierarchy.
/usr/spool -> /var/spool
/usr/tmp -> /var/tmp
/usr/spool/locks -> /var/lock
Once a system no longer requires any one of the above symbolic
links, the link may be removed, if desired.
4.4. /usr/bin : Most user commands
4.4.1. Purpose
This is the primary directory of executable commands on the
system.
4.4.2. Requirements
There must be no subdirectories in /usr/bin.
4.4.3. Specific Options
The following files, or symbolic links to files, must be in
/usr/bin, if the corresponding subsystem is installed:
Command Description
perl The Practical Extraction and Report Language (optional)
python The Python interpreted language (optional)
tclsh Simple shell containing Tcl interpreter (optional)
wish Simple Tcl/Tk windowing shell (optional)
expect Program for interactive dialog (optional)
Rationale
In many executable scripts, the interpreter to be invoked to
execute the script is specified using #!path_to_interpreter on
the first line of a script. To make such scripts portable among
different systems, it is advantageous to standardize the
interpreter locations. The shell interpreter is already fixed
in /bin by this specification, but interpreters for Perl,
Python, Tcl and expect may be installed in various places. The
locations specified here may be implemented as symbolic links
to the physical location of the interpreters.
4.5. /usr/include : Directory for standard include files.
4.5.1. Purpose
This is where all of the system's general-use include files for
the C programming language should be placed.
4.5.2. Specific Options
The following directories, or symbolic links to directories,
must be in /usr/include, if the corresponding subsystem is
installed:
Directory Description
bsd BSD compatibility include files (optional)
4.6. /usr/lib : Libraries for programming and packages
4.6.1. Purpose
/usr/lib includes object files and libraries. ^[21] On some
systems, it may also include internal binaries that are not
intended to be executed directly by users or shell scripts.
^[22]
Applications may use a single subdirectory under /usr/lib. If
an application uses a subdirectory, all architecture-dependent
data exclusively used by the application must be placed within
that subdirectory. ^[23]
4.6.2. Specific Options
For historical reasons, /usr/lib/sendmail must be a symbolic
link which resolves to the sendmail-compatible command provided
by the system's mail transfer agent, if the latter exists.
^[24] ^[25]
4.7. /usr/libexec : Binaries run by other programs (optional)
4.7.1. Purpose
/usr/libexec includes internal binaries that are not intended
to be executed directly by users or shell scripts. Applications
may use a single subdirectory under /usr/libexec.
Applications which use /usr/libexec in this way must not also
use /usr/lib to store internal binaries, though they may use
/usr/lib for the other purposes documented here.
Rationale
Some previous versions of this document did not support
/usr/libexec, despite it being standard practice in a number of
environments. ^[26] To accomodate this restriction, it became
common practice to use /usr/lib instead. Either practice is now
acceptable, but each application must choose one way or the
other to organize itself.
4.8. /usr/lib<qual> : Alternate format libraries (optional)
4.8.1. Purpose
/usr/lib<qual> performs the same role as /usr/lib for an
alternate binary format, except that the symbolic links
/usr/lib<qual>/sendmail and /usr/lib<qual>/X11 are not
required. ^[27]
4.9. /usr/local : Local hierarchy
4.9.1. Purpose
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. ^[28]
4.9.2. Requirements
The following directories, or symbolic links to directories,
must be in /usr/local
Directory Description
bin Local binaries
etc Host-specific system configuration for local binaries
games Local game binaries
include Local C header files
lib Local libraries
man Local online manuals
sbin Local system binaries
share Local architecture-independent hierarchy
src Local source code
No other directories, except those listed below, may be in
/usr/local after first installing a FHS-compliant system.
4.9.3. Specific Options
If directories /lib<qual> or /usr/lib<qual> exist, the
equivalent directories must also exist in /usr/local.
/usr/local/etc may be a symbolic link to /etc/local.
Rationale
The consistency of /usr/local/etc is beneficial to installers,
and is already used in other systems. As all of /usr/local
needs to be backed up to reproduce a system, it introduces no
additional maintenance overhead, but a symlink to /etc/local is
suitable if systems want all their configuration under one
hierarchy.
Note that /usr/etc is still not allowed: programs in /usr
should place configuration files in /etc.
If the directory /usr/share/color exists as specified in this
document, then the directory /usr/local/share/color must also
exist, governed by the same rules as /usr/share/color.
Rationale
This usage allows the sysadmin a place to install color
profiles manually when necessary.
4.9.4. /usr/local/share : Local architecture-independent hierarchy
The requirements for the contents of this directory are the
same as for /usr/share.
4.10. /usr/sbin : Non-essential standard system binaries
4.10.1. Purpose
This directory contains any non-essential binaries used
exclusively by the system administrator. System administration
programs that are required for system repair, system recovery,
mounting /usr, or other essential functions must be placed in
/sbin instead. ^[29]
4.10.2. Requirements
There must be no subdirectories in /usr/sbin.
4.11. /usr/share : Architecture-independent data
4.11.1. Purpose
The /usr/share hierarchy is for all read-only architecture
independent data files. ^[30]
This hierarchy is intended to be shareable among all
architecture platforms of a given OS; thus, for example, a site
with i386, Alpha, and PPC platforms might maintain a single
/usr/share directory that is centrally-mounted. Note, however,
that /usr/share is generally not intended to be shared by
different OSes or by different releases of the same OS.
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. Applications using a single file may use
/usr/share/misc.
Game data stored in /usr/share/games must be purely static
data. Any modifiable files, such as score files, game play
logs, and so forth, should be placed in /var/games.
4.11.2. Requirements
The following directories, or symbolic links to directories,
must be in /usr/share
Directory Description
man Online manuals
misc Miscellaneous architecture-independent data
4.11.3. Specific Options
The following directories, or symbolic links to directories,
must be in /usr/share, if the corresponding subsystem is
installed:
Directory Description
color Color management information (optional)
dict Word lists (optional)
doc Miscellaneous documentation (optional)
games Static data files for /usr/games (optional)
info Primary directory for GNU Info system (optional)
locale Locale information (optional)
nls Message catalogs for Native language support (optional)
ppd Printer definitions (optional)
sgml SGML data (optional)
terminfo Directories for terminfo database (optional)
tmac troff macros not distributed with groff (optional)
xml XML data (optional)
zoneinfo Timezone information and configuration (optional)
It is recommended that application-specific,
architecture-independent directories be placed here. Such
directories include groff, perl, ghostscript, texmf, and kbd
(Linux) or syscons (BSD). They may, however, be placed in
/usr/lib for backwards compatibility, at the distributor's
discretion. Similarly, a /usr/lib/games hierarchy may be used
in addition to the /usr/share/games hierarchy if the
distributor wishes to place some game data there.
4.11.4. /usr/share/color : Color management information (optional)
4.11.4.1. Purpose
This directory is the home for ICC color management files
installed by the system.
4.11.4.2. Specific Options
The following directories must be in /usr/share/color, if the
corresponding subsystem is installed:
Directory Description
icc ICC color profiles (optional)
The top-level directory /usr/share/color must not contain any
files; all files should be in subdirectories of
/usr/share/color.
4.11.5. /usr/share/dict : Word lists (optional)
4.11.5.1. Purpose
This directory is the home for word lists on the system;
Traditionally this directory contains only the English words
file, which is used by look(1) and various spelling programs.
words may use either American or British spelling.
Rationale
The reason that only word lists are located here is that they
are the only files common to all spell checkers.
4.11.5.2. Specific Options
The following files, or symbolic links to files, must be in
/usr/share/dict, if the corresponding subsystem is installed:
File Description
words List of English words (optional)
Sites that require both American and British spelling may link
words to /usr/share/dict/american-english or
/usr/share/dict/british-english.
Word lists for other languages may be added using the English
name for that language, e.g., /usr/share/dict/french,
/usr/share/dict/danish, etc. These should, if possible, use a
character set based on Unicode, with the UTF-8 character set
being the preferred option.
Other word lists must be included here, if present.
4.11.6. /usr/share/man : Manual pages
4.11.6.1. Purpose
This section details the organization for manual pages
throughout the system, including /usr/share/man. Also refer to
the section on /var/cache/man.
The primary <mandir> of the system is /usr/share/man.
/usr/share/man contains manual information for commands and
data under the / and /usr filesystems. ^[31]
Manual pages are stored in
<mandir>/<locale>/man<section>/<arch>. An explanation of
<mandir>, <locale>, <section>, and <arch> is given below.
A description of each section follows:
* 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.
4.11.6.2. Specific Options
The following directories, or symbolic links to directories,
must be in /usr/share/<mandir>/<locale>, unless they are empty:
^[32]
Directory Description
man1 User programs (optional)
man2 System calls (optional)
man3 Library calls (optional)
man4 Special files (optional)
man5 File formats (optional)
man6 Games (optional)
man7 Miscellaneous (optional)
man8 System administration (optional)
The component <section> describes the manual section.
Provisions must be made in the structure of /usr/share/man to
support manual pages which are written in different (or
multiple) languages. These provisions must take into account
the storage and reference of these manual pages. Relevant
factors include language (including geographical-based
differences), and character code set.
This naming of language subdirectories of /usr/share/man is
based on Appendix E of the POSIX 1003.1 standard which
describes the locale identification string — the most
well-accepted method to describe a cultural environment. The
<locale> string is:
<language>[_<territory>][.<character-set>][,<version>]
The <language> field must be taken from ISO 639 (a code for the
representation of names of languages). It must be two
characters wide and specified with lowercase letters only.
The <territory> field must be the two-letter code of ISO 3166
(a specification of representations of countries), if possible.
(Most people are familiar with the two-letter codes used for
the country codes in email addresses.) It must be two
characters wide and specified with uppercase letters only.
^[33]
The <character-set> field must represent the standard
describing the character set. If the <character-set> field is
just a numeric specification, the number represents the number
of the international standard describing the character set. It
is recommended that this be a numeric representation if
possible (ISO standards, especially), not include additional
punctuation symbols, and that any letters be in lowercase.
A parameter specifying a <version> of the profile may be placed
after the <character-set> field, delimited by a comma. This may
be used to discriminate between different cultural needs; for
instance, dictionary order versus a more systems-oriented
collating order. This standard recommends not using the
<version> field, unless it is necessary.
Systems which use a unique language and code set for all manual
pages may omit the <locale> substring and store all manual
pages in <mandir>. For example, systems which only have English
manual pages coded with ASCII, may store manual pages (the
man<section> directories) directly in /usr/share/man. (That is
the traditional circumstance and arrangement, in fact.)
Countries for which there is a well-accepted standard character
code set may omit the <character-set> field, but it is strongly
recommended that it be included, especially for countries with
several competing standards.
Various examples:
Language Territory Character Set Directory
English — ASCII /usr/share/man/en
English United Kingdom Unicode UTF-8 /usr/share/man/en_GB.10646
English United States ASCII /usr/share/man/en_US
French Canada ISO 8859-1 /usr/share/man/fr_CA.88591
French France ISO 8859-1 /usr/share/man/fr_FR.88591
German Germany ISO 646 /usr/share/man/de_DE.646
German Germany ISO 6937 /usr/share/man/de_DE.6937
German Germany ISO 8859-1 /usr/share/man/de_DE.88591
German Switzerland ISO 646 /usr/share/man/de_CH.646
Japanese Japan JIS /usr/share/man/ja_JP.jis
Japanese Japan SJIS /usr/share/man/ja_JP.sjis
Japanese Japan UJIS (or EUC-J) /usr/share/man/ja_JP.ujis
Japanese Japan Unicode UTF-16 /usr/share/man/ja_JP.10646
Similarly, provision must be made for manual pages which are
architecture-dependent, such as documentation on device-drivers
or low-level system administration commands. These must be
placed under an <arch> directory in the appropriate
man<section> directory; for example, a man page for the i386
ctrlaltdel(8) command might be placed in
/usr/share/man/<locale>/man8/i386/ctrlaltdel.8.
Manual pages for commands and data under /usr/local are stored
in /usr/local/man or /usr/local/share/man. All manual page
hierarchies in the system must have the same structure as
/usr/share/man, as this structure is expected by commands which
consume manual page content. ^[34]
The cat page sections (cat<section>) containing formatted
manual page entries are also found within subdirectories of
<mandir>/<locale>, but are not required nor may they be
distributed in lieu of nroff source manual pages.
The numbered sections "1" through "8" are traditionally
defined. In general, the file name for manual pages located
within a particular section end with .<section>.
In addition, some large sets of application-specific manual
pages have an additional suffix appended to the manual page
filename. For example, the MH mail handling system manual pages
must have mh appended to all MH manuals. All X Window System
manual pages must have an x appended to the filename.
The practice of placing various language manual pages in
appropriate subdirectories of /usr/share/man also applies to
the other manual page hierarchies, such as /usr/local/man.
(This portion of the standard also applies later in the section
on the optional /var/cache/man structure.)
4.11.7. /usr/share/misc : Miscellaneous architecture-independent data
This directory contains miscellaneous architecture-independent
files which don't require a separate subdirectory under
/usr/share.
4.11.7.1. Specific Options
The following files, or symbolic links to files, must be in
/usr/share/misc, if the corresponding subsystem is installed:
File Description
ascii ASCII character set table (optional)
termcap Terminal capability database (optional)
termcap.db Terminal capability database (optional)
Other (application-specific) files may appear here, but a
distributor may place them in /usr/lib at their discretion.
^[35] ^[36]
4.11.8. /usr/share/ppd : Printer definitions (optional)
4.11.8.1. Purpose
/usr/share/ppd contains PostScript Printer Definition (PPD)
files, which are used as descriptions of printer drivers by
many print systems. PPD files may be placed in this directory,
or in a subdirectory.
4.11.9. /usr/share/sgml : SGML data (optional)
4.11.9.1. Purpose
/usr/share/sgml contains architecture-independent files used by
SGML applications, such as ordinary catalogs (not the
centralized ones, see /etc/sgml), DTDs, entities, or style
sheets.
4.11.9.2. Specific Options
The following directories, or symbolic links to directories,
must be in /usr/share/sgml, if the corresponding subsystem is
installed:
Directory Description
docbook docbook DTD (optional)
tei tei DTD (optional)
html html DTD (optional)
mathml mathml DTD (optional)
Other files that are not specific to a given DTD may reside in
their own subdirectory.
4.11.10. /usr/share/xml : XML data (optional)
4.11.10.1. Purpose
/usr/share/xml contains architecture-independent files used by
XML applications, such as ordinary catalogs (not the
centralized ones, see /etc/sgml), DTDs, entities, or style
sheets.
4.11.10.2. Specific Options
The following directories, or symbolic links to directories,
must be in /usr/share/xml, if the corresponding subsystem is
installed:
Directory Description
docbook docbook XML DTD (optional)
xhtml XHTML DTD (optional)
mathml MathML DTD (optional)
4.12. /usr/src : Source code (optional)
4.12.1. Purpose
Source code may be placed in this subdirectory, only for
reference purposes. ^[37]
__________________________________________________________
^[21] Miscellaneous architecture-independent
application-specific static files and subdirectories must be
placed in /usr/share.
^[22] See below, in the /usr/libexec section, for a discussion
of /usr/lib vs. /usr/libexec for executable binaries.
^[23] For example, the perl5 subdirectory for Perl 5 modules
and libraries.
^[24] Some executable commands such as makewhatis and sendmail
have also been traditionally placed in /usr/lib. makewhatis is
an internal binary and must be placed in a binary directory;
users access only catman. Newer sendmail binaries are now
placed by default in /usr/sbin. Additionally, systems using a
sendmail-compatible mail transfer agent must provide
/usr/sbin/sendmail as the sendmail command, either as the
executable itself or as a symlink to the appropriate
executable.
^[25] Host-specific data for the X Window System must not be
stored in /usr/lib/X11. Host-specific configuration files such
as xorg.conf must be stored in /etc/X11. This includes
configuration data such as system.twmrc even if it is only made
a symbolic link to a more global configuration file (probably
in /usr/lib/X11).
^[26] See, for example, the "GNU Coding Standards" from the
Free Software Foundation.
^[27] The case where /usr/lib and /usr/lib<qual> are the same
(one is a symbolic link to the other) these files and the
per-application subdirectories will exist.
^[28] Software placed in / or /usr may be overwritten by system
upgrades (though we recommend that distributions do not
overwrite data in /etc under these circumstances). For this
reason, local software must not be placed outside of /usr/local
without good reason.
^[29] Locally installed system administration programs should
be placed in /usr/local/sbin.
^[30] Much of this data originally lived in /usr (man, doc) or
/usr/lib (dict, terminfo, zoneinfo).
^[31] Obviously, there are no manual pages in / because they
are not required at boot time nor are they required in
emergencies. Really.
^[32] For example, if /usr/share/man has no manual pages in
section 4 (Devices), then /usr/share/man/man4 may be omitted.
^[33] A major exception to this rule is the United Kingdom,
which is `GB' in the ISO 3166, but `UK' for most email
addresses.
^[34] /usr/local/man is deprecated and may be dropped in a
future version of this specification.
^[35] Some such files include: airport, birthtoken, eqnchar,
getopt, gprof.callg, gprof.flat, inter.phone,
ipfw.samp.filters, ipfw.samp.scripts, keycap.pcvt, mail.help,
mail.tildehelp, man.template, map3270, mdoc.template,
more.help, na.phone, nslookup.help, operator, scsi_modes,
sendmail.hf, style, units.lib, vgrindefs, vgrindefs.db,
zipcodes.
^[36] Historically, the magic file was placed in
/usr/share/misc, but modern variants of the file command use
several files and place them in /usr/share/file. For
compatibility, distribution may create a symlink at
/usr/share/misc/magic, pointing to /usr/share/file/magic.
^[37] Generally, source should not be built within this
hierarchy.
Chapter 5. The /var Hierarchy
Table of Contents
5.1. Purpose
5.2. Requirements
5.3. Specific Options
5.4. /var/account : Process accounting logs (optional)
5.4.1. Purpose
5.5. /var/cache : Application cache data
5.5.1. Purpose
5.5.2. Specific Options
5.5.3. /var/cache/fonts : Locally-generated fonts
(optional)
5.5.4. /var/cache/man : Locally-formatted manual pages
(optional)
5.6. /var/crash : System crash dumps (optional)
5.6.1. Purpose
5.7. /var/games : Variable game data (optional)
5.7.1. Purpose
5.8. /var/lib : Variable state information
5.8.1. Purpose
5.8.2. Requirements
5.8.3. Specific Options
5.8.4. /var/lib/<editor> : Editor backup files and state
(optional)
5.8.5. /var/lib/color : Color management information
(optional)
5.8.6. /var/lib/hwclock : State directory for hwclock
(optional)
5.8.7. /var/lib/misc : Miscellaneous variable data
5.9. /var/lock : Lock files
5.9.1. Purpose
5.10. /var/log : Log files and directories
5.10.1. Purpose
5.10.2. Specific Options
5.11. /var/mail : User mailbox files (optional)
5.11.1. Purpose
5.12. /var/opt : Variable data for /opt
5.12.1. Purpose
5.13. /var/run : Run-time variable data
5.13.1. Purpose
5.13.2. Requirements
5.14. /var/spool : Application spool data
5.14.1. Purpose
5.14.2. Specific Options
5.14.3. /var/spool/lpd : Line-printer daemon print queues
(optional)
5.14.4. /var/spool/rwho : Rwhod files (optional)
5.15. /var/tmp : Temporary files preserved between system
reboots
5.15.1. Purpose
5.16. /var/yp : Network Information Service (NIS) database
files (optional)
5.16.1. Purpose
5.1. Purpose
/var contains variable data files. This includes spool
directories and files, administrative and logging data, 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.
/var is specified here in order to make it possible to mount
/usr read-only. Everything that once went into /usr that is
written to during system operation (as opposed to installation
and software maintenance) must be in /var.
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.
5.2. Requirements
The following directories, or symbolic links to directories,
are required in /var:
Directory Description
cache Application cache data
lib Variable state information
local Variable data for /usr/local
lock Lock files
log Log files and directories
opt Variable data for /opt
run Data relevant to running processes
spool Application spool data
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
5.3. Specific Options
The following directories, or symbolic links to directories,
must be in /var, if the corresponding subsystem is installed:
Directory Description
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)
5.4. /var/account : Process accounting logs (optional)
5.4.1. Purpose
This directory holds the current active process accounting log
and the composite process usage data (as used in some UNIX-like
systems by lastcomm and sa).
5.5. /var/cache : Application cache data
5.5.1. Purpose
/var/cache is intended for cached data from applications. Such
data is locally generated as a result of time-consuming I/O or
calculation. The application must be able to regenerate or
restore the data. Unlike /var/spool, the cached files can be
deleted without data loss. The data must remain valid between
invocations of the application and rebooting the system.
Files located under /var/cache may be expired in an application
specific manner, by the system administrator, or both. The
application must always be able to recover from manual deletion
of these files (generally because of a disk space shortage). No
other requirements are made on the data format of the cache
directories.
Rationale
The existence of a separate directory for cached data allows
system administrators to set different disk and backup policies
from other directories in /var.
5.5.2. Specific Options
Directory Description
fonts Locally-generated fonts (optional)
man Locally-formatted manual pages (optional)
www WWW proxy or cache data (optional)
<package> Package specific cache data (optional)
5.5.3. /var/cache/fonts : Locally-generated fonts (optional)
5.5.3.1. Purpose
The directory /var/cache/fonts should be used to store any
dynamically-created fonts. In particular, all of the fonts
which are automatically generated by mktexpk must be located in
appropriately-named subdirectories of /var/cache/fonts. ^[38]
5.5.3.2. Specific Options
Other dynamically created fonts may also be placed in this
tree, under appropriately-named subdirectories of
/var/cache/fonts.
5.5.4. /var/cache/man : Locally-formatted manual pages (optional)
5.5.4.1. Purpose
This directory provides a standard location for sites that
provide a read-only /usr partition, but wish to allow caching
of locally-formatted man pages. Sites that mount /usr as
writable (e.g., single-user installations) may choose not to
use /var/cache/man and may write formatted man pages into the
cat<section> directories in /usr/share/man directly. We
recommend that most sites use one of the following options
instead:
* Preformat all manual pages alongside the unformatted
versions.
* Allow no caching of formatted man pages, and require
formatting to be done each time a man page is brought up.
* Allow local caching of formatted man pages in
/var/cache/man.
The structure of /var/cache/man needs to reflect both the fact
of multiple man page hierarchies and the possibility of
multiple language support.
Given an unformatted manual page that normally appears in
<path>/man/<locale>/man<section>, the directory to place
formatted man pages in is
/var/cache/man/<catpath>/<locale>/cat<section>, where <catpath>
is derived from <path> by removing any leading usr and/or
trailing share pathname components. (Note that the <locale>
component may be missing.) ^[39]
Man pages written to /var/cache/man may eventually be
transferred to the appropriate preformatted directories in the
source man hierarchy or expired; likewise formatted man pages
in the source man hierarchy may be expired if they are not
accessed for a period of time.
If preformatted manual pages come with a system on read-only
media (a CD-ROM, for instance), they must be installed in the
source man hierarchy (e.g. /usr/share/man/cat<section>).
/var/cache/man is reserved as a writable cache for formatted
manual pages.
Rationale
Release 1.2 of this standard specified /var/catman for this
hierarchy. The path has been moved under /var/cache to better
reflect the dynamic nature of the formatted man pages. The
directory name has been changed to man to allow for enhancing
the hierarchy to include post-processed formats other than
"cat", such as PostScript, HTML, or DVI.
5.6. /var/crash : System crash dumps (optional)
5.6.1. Purpose
This directory holds system crash dumps. As of the date of this
release of the standard, system crash dumps were not supported
under Linux but may be supported by other systems which may
comply with the FHS.
5.7. /var/games : Variable game data (optional)
5.7.1. Purpose
Any variable data relating to games in /usr should be placed
here. /var/games should hold the variable data previously found
in /usr; static data, such as help text, level descriptions,
and so on, must remain elsewhere, such as /usr/share/games.
Rationale
/var/games has been given a hierarchy of its own, rather than
leaving it underneath /var/lib as in release 1.2 of this
standard. The separation 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.
5.8. /var/lib : Variable state information
5.8.1. Purpose
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 must never need to modify files in
/var/lib to configure a package's operation, and the specific
file hierarchy used to store the data must not be exposed to
regular users. ^[40]
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. State information should generally remain valid
after a reboot, should not be logging output, and should not be
spooled data.
An application (or a group of inter-related applications) must
use a subdirectory of /var/lib for its data. There is one
required 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. ^[41]
/var/lib/<name> is the location that must be used for all
distribution packaging support. Different distributions may use
different names, of course.
5.8.2. Requirements
The following directories, or symbolic links to directories,
are required in /var/lib:
Directory Description
misc Miscellaneous state data
5.8.3. Specific Options
The following directories, or symbolic links to directories,
must be in /var/lib, if the corresponding subsystem is
installed:
Directory Description
<editor> Editor backup files and state (optional)
<pkgtool> Packaging support files (optional)
<package> State data for packages and subsystems (optional)
color Color management information (optional)
hwclock State directory for hwclock (optional)
xdm X display manager variable data (optional)
5.8.4. /var/lib/<editor> : Editor backup files and state (optional)
5.8.4.1. Purpose
These directories contain saved files generated by any
unexpected termination of an editor (e.g., elvis, jove, nvi).
Other editors may not require a directory for crash-recovery
files, but may require a well-defined place to store other
information while the editor is running. This information
should be stored in a subdirectory under /var/lib (for example,
GNU Emacs would place lock files in /var/lib/emacs/lock).
Future editors may require additional state information beyond
crash-recovery files and lock files — this information should
also be placed under /var/lib/<editor>.
Rationale
Previous Linux releases, as well as all commercial vendors, use
/var/preserve for vi or its clones. However, each editor uses
its own format for these crash-recovery files, so a separate
directory is needed for each editor.
Editor-specific lock files are usually quite different from the
device or resource lock files that are stored in /var/lock and,
hence, are stored under /var/lib.
5.8.5. /var/lib/color : Color management information (optional)
5.8.5.1. Purpose
This directory is the home for ICC color management files
installed dynamically. This directory shall be laid out using
the same rules as the /usr/share/color directory.
5.8.6. /var/lib/hwclock : State directory for hwclock (optional)
5.8.6.1. Purpose
This directory contains the file /var/lib/hwclock/adjtime.
Rationale
In FHS 2.1, this file was /etc/adjtime, but as hwclock updates
it, that was obviously incorrect.
5.8.7. /var/lib/misc : Miscellaneous variable data
5.8.7.1. Purpose
This directory contains variable data not placed in a
subdirectory in /var/lib. An attempt should be made to use
relatively unique names in this directory to avoid namespace
conflicts. ^[42]
5.9. /var/lock : Lock files
5.9.1. Purpose
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. For example, to lock /dev/ttyS0 the file "LCK..ttyS0"
would be created. ^[43]
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.
5.10. /var/log : Log files and directories
5.10.1. Purpose
This directory contains miscellaneous log files. Most logs must
be written to this directory or an appropriate subdirectory.
5.10.2. Specific Options
The following files, or symbolic links to files, must be in
/var/log, if the corresponding subsystem is installed:
File Description
lastlog record of last login of each user
messages system messages from syslogd
wtmp record of all logins and logouts
5.11. /var/mail : User mailbox files (optional)
5.11.1. Purpose
The mail spool must be accessible through /var/mail and the
mail spool files must take the form <username>. ^[44]
User mailbox files in this location must be stored in the
standard UNIX mailbox format.
Rationale
The logical location for this directory was changed from
/var/spool/mail in order to bring FHS in-line with nearly every
UNIX distribution. This change is important for
inter-operability since a single /var/mail is often shared
between multiple hosts and multiple UNIX distribution (despite
NFS locking issues).
It is important to note that there is no requirement to
physically move the mail spool to this location. However,
programs and header files must be changed to use /var/mail.
5.12. /var/opt : Variable data for /opt
5.12.1. Purpose
Variable data of the packages in /opt must be installed in
/var/opt/<subdir>, where <subdir> is the name of the subtree in
/opt where the static data from an add-on software package is
stored, except where superseded by another file in /etc. No
structure is imposed on the internal arrangement of
/var/opt/<subdir>.
Rationale
Refer to the rationale for /opt.
5.13. /var/run : Run-time variable data
5.13.1. Purpose
This directory was once intended for system information data
describing the system since it was booted. These functions have
been moved to /run; this directory exists to ensure
compatibility with systems and software using an older version
of this specification.
5.13.2. Requirements
In general, the requirements for /run shall also apply to
/var/run. It is valid to implement /var/run as a symlink to
/run.
The utmp file, which stores information about who is currently
using the system, is located in this directory.
Programs should not access both /var/run and /run directly,
except to access /var/run/utmp. ^[45]
5.14. /var/spool : Application spool data
5.14.1. Purpose
/var/spool contains data which is awaiting some kind of later
processing. Data in /var/spool represents work to be done in
the future (by a program, user, or administrator); often data
is deleted after it has been processed. ^[46]
5.14.2. Specific Options
The following directories, or symbolic links to directories,
must be in /var/spool, if the corresponding subsystem is
installed:
Directory Description
lpd Printer spool directory (optional)
mqueue Outgoing mail queue (optional)
news News spool directory (optional)
rwho Rwhod files (optional)
uucp Spool directory for UUCP (optional)
5.14.3. /var/spool/lpd : Line-printer daemon print queues (optional)
5.14.3.1. Purpose
The lock file for lpd, lpd.lock, must be placed in
/var/spool/lpd. It is suggested that the lock file for each
printer be placed in the spool directory for that specific
printer and named lock.
5.14.3.2. Specific Options
Directory Description
printer Spools for a specific printer (optional)
5.14.4. /var/spool/rwho : Rwhod files (optional)
5.14.4.1. Purpose
This directory holds the rwhod information for other systems on
the local net.
Rationale
Some BSD releases use /var/rwho for this data; given its
historical location in /var/spool on other systems and its
approximate fit to the definition of `spooled' data, this
location was deemed more appropriate.
5.15. /var/tmp : Temporary files preserved between system reboots
5.15.1. Purpose
The /var/tmp directory is made available for programs that
require temporary files or directories that are preserved
between system reboots. Therefore, data stored in /var/tmp is
more persistent than data in /tmp.
Files and directories located in /var/tmp must not be deleted
when the system is booted. Although data stored in /var/tmp is
typically deleted in a site-specific manner, it is recommended
that deletions occur at a less frequent interval than /tmp.
5.16. /var/yp : Network Information Service (NIS) database files
(optional)
5.16.1. Purpose
Variable data for the Network Information Service (NIS),
formerly known as the Sun Yellow Pages (YP), must be placed in
this directory.
Rationale
/var/yp is the standard directory for NIS (YP) data and is
almost exclusively used in NIS documentation and systems. ^[47]
__________________________________________________________
^[38] This standard does not currently incorporate the TeX
Directory Structure (a document that describes the layout TeX
files and directories), but it may be useful reading. It is
located at ftp://ctan.tug.org/tex/
^[39] For example, /usr/share/man/man1/ls.1 is formatted into
/var/cache/man/cat1/ls.1, and
/usr/X11R6/man/<locale>/man3/XtClass.3x into
/var/cache/man/X11R6/<locale>/cat3/XtClass.3x.
^[40] Data with exposed filesystem structure should be stored
in /srv.
^[41] An important difference between this version of this
standard and previous ones is that applications are now
required to use a subdirectory of /var/lib.
^[42] This hierarchy should contain files stored in /var/db in
current BSD releases. These include locate.database and
mountdtab, and the kernel symbol database(s).
^[43] Then, anything wishing to use /dev/ttyS0 can read the
lock file and act accordingly (all locks in /var/lock should be
world-readable).
^[44] Note that /var/mail may be a symbolic link to another
directory.
^[45] This is to prevent confusion about where transient files
are located. In general, a program should use either /var/run
or /run to access these files, not both.
^[46] UUCP lock files must be placed in /var/lock. See the
above section on /var/lock.
^[47] NIS should not be confused with Sun NIS+, which uses a
different directory, /var/nis.
Chapter 6. Operating System Specific Annex
Table of Contents
6.1. Linux
6.1.1. / : Root directory
6.1.2. /bin : Essential user command binaries (for use by
all users)
6.1.3. /dev : Devices and special files
6.1.4. /etc : Host-specific system configuration
6.1.5. /proc : Kernel and process information virtual
filesystem
6.1.6. /sbin : Essential system binaries
6.1.7. /sys : Kernel and system information virtual
filesystem
6.1.8. /usr/include : Header files included by C programs
6.1.9. /usr/src : Source code
6.1.10. /var/spool/cron : cron and at jobs
This section is for additional requirements and recommendations
that only apply to a specific operating system. The material in
this section should never conflict with the base standard.
6.1. Linux
This is the annex for the Linux operating system.
6.1.1. / : Root directory
On Linux systems, if the kernel is located in /, we recommend
using the names vmlinux or vmlinuz, which have been used in
recent Linux kernel source packages.
6.1.2. /bin : Essential user command binaries (for use by all users)
Linux systems which require them place these additional files
into /bin:
* setserial
6.1.3. /dev : Devices and special files
The following devices must exist under /dev.
/dev/null
All data written to this device is discarded. A read
from this device will return an EOF condition.
/dev/zero
This device is a source of zeroed out data. All data
written to this device is discarded. A read from this
device will return as many bytes containing the value
zero as was requested.
/dev/tty
This device is a synonym for the controlling terminal of
a process. Once this device is opened, all reads and
writes will behave as if the actual controlling terminal
device had been opened.
Rationale
Previous versions of the FHS had stricter requirements for
/dev. Other devices may also exist in /dev. Device names may
exist as symbolic links to other device nodes located in /dev
or subdirectories of /dev. There is no requirement concerning
major/minor number values.
6.1.4. /etc : Host-specific system configuration
Linux systems which require them place these additional files
into /etc.
* lilo.conf
6.1.5. /proc : Kernel and process information virtual filesystem
The proc filesystem is the de-facto standard Linux method for
handling process and system information, rather than /dev/kmem
and other similar methods. We strongly encourage this for the
storage and retrieval of process information as well as other
kernel and memory information.
6.1.6. /sbin : Essential system binaries
Linux systems place commands relating to filesystem maintenance
and boot loader management into /sbin.
Optional files for /sbin:
* Static binaries:
+ ldconfig
+ sln
+ ssync
Static ln (sln) and static sync (ssync) are useful when
things go wrong. The primary use of sln (to repair
incorrect symlinks in /lib after a poorly orchestrated
upgrade) is no longer a major concern now that the ldconfig
program (usually located in /usr/sbin) exists and can act
as a guiding hand in upgrading the dynamic libraries.
Static sync is useful in some emergency situations. Note
that these need not be statically linked versions of the
standard ln and sync, but may be.
The ldconfig binary is optional for /sbin since a site may
choose to run ldconfig at boot time, rather than only when
upgrading the shared libraries. (It's not clear whether or
not it is advantageous to run ldconfig on each boot.) Even
so, some people like ldconfig around for the following (all
too common) situation:
1. I've just removed /lib/<file>.
2. I can't find out the name of the library because ls is
dynamically linked, I'm using a shell that doesn't
have ls built-in, and I don't know about using "echo
*" as a replacement.
3. I have a static sln, but I don't know what to call the
link.
* Miscellaneous:
+ ctrlaltdel
+ kbdrate
So as to cope with the fact that some keyboards come up
with such a high repeat rate as to be unusable, kbdrate may
be installed in /sbin on some systems.
Since the default action in the kernel for the Ctrl-Alt-Del
key combination is an instant hard reboot, it is generally
advisable to disable the behavior before mounting the root
filesystem in read-write mode. Some init suites are able to
disable Ctrl-Alt-Del, but others may require the ctrlaltdel
program, which may be installed in /sbin on those systems.
6.1.7. /sys : Kernel and system information virtual filesystem
The sys filesystem is the location where information about
devices, drivers, and some kernel features is exposed. Its
underlying structure is determined by the particular Linux
kernel being used at the moment, and is otherwise unspecified.
6.1.8. /usr/include : Header files included by C programs
These symbolic links are required if a C or C++ compiler is
installed and only for systems not based on glibc.
/usr/include/asm -> /usr/src/linux/include/asm-<arch>
/usr/include/linux -> /usr/src/linux/include/linux
6.1.9. /usr/src : Source code
For systems based on glibc, there are no specific guidelines
for this directory. For systems based on Linux libc revisions
prior to glibc, the following guidelines and rationale apply:
The only source code that should be placed in a specific
location is the Linux kernel source code. It is located in
/usr/src/linux.
If a C or C++ compiler is installed, but the complete Linux
kernel source code is not installed, then the include files
from the kernel source code must be located in these
directories:
/usr/src/linux/include/asm-<arch>
/usr/src/linux/include/linux
<arch> is the name of the system architecture.
Note
/usr/src/linux may be a symbolic link to a kernel source code
tree.
Rationale
It is important that the kernel include files be located in
/usr/src/linux and not in /usr/include so there are no problems
when system administrators upgrade their kernel version for the
first time.
6.1.10. /var/spool/cron : cron and at jobs
This directory contains the variable data for the cron and at
programs.
Chapter 7. Appendix
Table of Contents
7.1. The FHS mailing list
7.2. Background of the FHS
7.3. General Guidelines
7.4. Scope
7.5. Acknowledgments
7.6. Contributors
7.1. The FHS mailing list
The FHS mailing list is located at
<fhs-discuss@lists.linuxfoundation.org> (subscription required
as a spam limitation measure). Mailing list subscription
information, archives, etc. are at
https://lists.linux-foundation.org/mailman/listinfo/fhs-discuss
7.2. Background of the FHS
The process of developing a standard filesystem hierarchy began
in August 1993 with an effort to restructure the file and
directory structure of Linux. The FSSTND, a filesystem
hierarchy standard specific to the Linux operating system, was
released on February 14, 1994. Subsequent revisions were
released on October 9, 1994 and March 28, 1995.
In early 1995, the goal of developing a more comprehensive
version of FSSTND to address not only Linux, but other
UNIX-like systems was adopted with the help of members of the
BSD development community. As a result, a concerted effort was
made to focus on issues that were general to UNIX-like systems.
In recognition of this widening of scope, the name of the
standard was changed to Filesystem Hierarchy Standard or FHS
for short.
Volunteers who have contributed extensively to this standard
are listed at the end of this document. This standard
represents a consensus view of those and other contributors.
Thanks to Network Operations at the University of California at
San Diego, and later to SourceForge, who allowed us to use
their excellent mailing list servers during earlier phases of
development.
7.3. General Guidelines
Here are some of the guidelines that have been used in the
development of this standard:
* Solve technical problems while limiting transitional
difficulties.
* Make the specification reasonably stable.
* Gain the approval of distributors, developers, and other
decision-makers in relevant development groups and
encourage their participation.
* Provide a standard that is attractive to the implementors
of different UNIX-like systems.
7.4. Scope
This document specifies a standard filesystem hierarchy for FHS
filesystems by specifying the location of files and
directories, and the contents of some system files.
This standard has been designed to be used by system
integrators, package developers, and system administrators in
the construction and maintenance of FHS compliant filesystems.
It is primarily intended to be a reference and is not a
tutorial on how to manage a conforming filesystem hierarchy.
The FHS grew out of earlier work on FSSTND, a filesystem
organization standard for the Linux operating system. It builds
on FSSTND to address interoperability issues not just in the
Linux community but in a wider arena including 4.4BSD-based
operating systems. It incorporates lessons learned in the BSD
world and elsewhere about multi-architecture support and the
demands of heterogeneous networking.
Although this standard is more comprehensive than previous
attempts at filesystem hierarchy standardization, periodic
updates may become necessary as requirements change in relation
to emerging technology. It is also possible that better
solutions to the problems addressed here will be discovered so
that our solutions will no longer be the best possible
solutions. Supplementary drafts may be released in addition to
periodic updates to this document. However, a specific goal is
backwards compatibility from one release of this document to
the next.
Comments related to this standard are welcome. Any comments or
suggestions for changes may be directed to the FHS mailing
list, or filed as bugs, or both. Typographical or grammatical
comments should be filed as bugs. The bugtracker is at
http://bugs.linuxfoundation.org - use the category FHS.
Before sending mail to the mailing list it is requested that
you first glance at the mailing list archives to avoid
excessive re-discussion of old topics.
Questions about how to interpret items in this document may
occasionally arise. If you have need for a clarification,
please contact the FHS mailing list. Since this standard
represents a consensus of many participants, it is important to
make certain that any interpretation also represents their
collective opinion. For this reason it may not be possible to
provide an immediate response unless the inquiry has been the
subject of previous discussion.
7.5. Acknowledgments
The developers of the FHS wish to thank the developers, system
administrators, and users whose input was essential to this
standard. We wish to thank each of the contributors who helped
to write, compile, and compose this standard.
The FHS Group also wishes to thank those Linux developers who
supported the FSSTND, the predecessor to this standard. If they
hadn't demonstrated that the FSSTND was beneficial, the FHS
could never have evolved.
7.6. Contributors
Brandon S. Allbery John A. Martin Mike Sangrey
Keith Bostic Ian McCloghrie David H. Silber
Drew Eckhardt Chris Metcalf Thomas Sippel-Dau
Rik Faith Ian Murdock Theodore Ts'o
Karl Goetz David C. Niemi Stephen Tweedie
Stephen Harris Lennart Poettering Fred N. van Kempen
Ian Jackson Daniel Quinlan Bernd Warken
Andreas Jaeger Eric S. Raymond Mats Wichmann
Jeff Licquia Rusty Russell Christopher Yeoh
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