Filesystem Hierarchy Standard Group
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Filesystem Hierarchy Standard Group
Edited by
Rusty Russell
Daniel Quinlan
Christopher Yeoh
Copyright © 1994-2004 Daniel Quinlan
Copyright © 2001-2004 Paul 'Rusty' Russell
Copyright © 2003-2004 Christopher Yeoh
Thisstandard consists of a set of requirements and guidelines for file anddirectory placement under UNIX-like operating systems. The guidelinesare intended to support interoperability of applications, systemadministration tools, development tools, and scripts as well as greateruniformity of documentation for these systems.
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Permission is granted to copy and distribute modifiedversions of this standard under the conditions for verbatim copying,provided also that the title page is labeled as modified including areference to the original standard, provided that information onretrieving the original standard is included, and provided that theentire resulting derived work is distributed under the terms of apermission notice identical to this one.
Permission is granted tocopy and distribute translations of this standard into anotherlanguage, under the above conditions for modified versions, except thatthis permission notice may be stated in a translation approved by thecopyright holder.
- Table of Contents
- 1. Introduction
- Purpose
- Conventions
- 2. The Filesystem
- 3. The Root Filesystem
- Purpose
- Requirements
- Specific Options
- /bin : Essential user command binaries (for use by all users)
- Purpose
- Requirements
- Specific Options
- /boot : Static files of the boot loader
- Purpose
- Specific Options
- /dev : Device files
- Purpose
- Specific Options
- /etc : Host-specific system configuration
- Purpose
- Requirements
- Specific Options
- /etc/opt : Configuration files for /opt
- /etc/X11 : Configuration for the X Window System (optional)
- /etc/sgml : Configuration files for SGML (optional)
- /etc/xml : Configuration files for XML (optional)
- /home : User home directories (optional)
- Purpose
- Requirements
- /lib : Essential shared libraries and kernel modules
- Purpose
- Requirements
- Specific Options
- /lib<qual> : Alternate format essential shared libraries (optional)
- Purpose
- Requirements
- /media : Mount point for removeable media
- Purpose
- Specific Options
- /mnt : Mount point for a temporarily mounted filesystem
- Purpose
- /opt : Add-on application software packages
- Purpose
- Requirements
- /root : Home directory for the root user (optional)
- Purpose
- /sbin : System binaries
- Purpose
- Requirements
- Specific Options
- /srv : Data for services provided by this system
- Purpose
- /tmp : Temporary files
- Purpose
- 4. The /usr Hierarchy
- Purpose
- Requirements
- Specific Options
- /usr/X11R6 : X Window System, Version 11 Release 6 (optional)
- Purpose
- Specific Options
- /usr/bin : Most user commands
- Purpose
- Specific Options
- /usr/include : Directory for standard include files.
- Purpose
- Specific Options
- /usr/lib : Libraries for programming and packages
- Purpose
- Specific Options
- /usr/lib<qual> : Alternate format libraries (optional)
- Purpose
- /usr/local : Local hierarchy
- /usr/local/share
- /usr/sbin : Non-essential standard system binaries
- Purpose
- /usr/share : Architecture-independent data
- Purpose
- Requirements
- Specific Options
- /usr/share/dict : Word lists (optional)
- /usr/share/man : Manual pages
- /usr/share/misc : Miscellaneous architecture-independent data
- /usr/share/sgml : SGML data (optional)
- /usr/share/xml : XML data (optional)
- /usr/src : Source code (optional)
- Purpose
- 5. The /var Hierarchy
- Purpose
- Requirements
- Specific Options
- /var/account : Process accounting logs (optional)
- Purpose
- /var/cache : Application cache data
- Purpose
- Specific Options
- /var/cache/fonts : Locally-generated fonts (optional)
- /var/cache/man : Locally-formatted manual pages (optional)
- /var/crash : System crash dumps (optional)
- Purpose
- /var/games : Variable game data (optional)
- Purpose
- /var/lib : Variable state information
- Purpose
- Requirements
- Specific Options
- /var/lib/<editor> : Editor backup files and state (optional)
- /var/lib/hwclock : State directory for hwclock (optional)
- /var/lib/misc : Miscellaneous variable data
- /var/lock : Lock files
- Purpose
- /var/log : Log files and directories
- Purpose
- Specific Options
- /var/mail : User mailbox files (optional)
- Purpose
- /var/opt : Variable data for /opt
- Purpose
- /var/run : Run-time variable data
- Purpose
- Requirements
- /var/spool : Application spool data
- Purpose
- Specific Options
- /var/spool/lpd : Line-printer daemon print queues (optional)
- /var/spool/rwho : Rwhod files (optional)
- /var/tmp : Temporary files preserved between system reboots
- Purpose
- /var/yp : Network Information Service (NIS) database files (optional)
- Purpose
- 6. Operating System Specific Annex
- Linux
- / : Root directory
- /bin : Essential user command binaries (for use by all users)
- /dev : Devices and special files
- /etc : Host-specific system configuration
- /lib64 and /lib32 : 64/32-bit libraries (architecture dependent)
- /proc : Kernel and process information virtual filesystem
- /sbin : Essential system binaries
- /usr/include : Header files included by C programs
- /usr/src : Source code
- /var/spool/cron : cron and at jobs
- 7. Appendix
- The FHS mailing list
- Background of the FHS
- General Guidelines
- Scope
- Acknowledgments
- Contributors
Chapter 1. Introduction
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:
Independentsoftware suppliers to create applications which are FHS compliant, andwork with distributions which are FHS complaint,
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.
FHSaddresses issues where file placements need to be coordinated betweenmultiple parties such as local sites, distributions, applications,documentation, etc.
Conventions
Werecommend that you read a typeset version of this document rather thanthe plain text version. In the typeset version, the names of files anddirectories 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
Thisstandard assumes that the operating system underlying an FHS-compliantfile system supports the same basic security features found in mostUNIX filesystems.
It is possible to define two independentdistinctions among files: shareable vs. unshareable and variable vs.static. In general, files that differ in either of these respectsshould be located in different directories. This makes it easy to storefiles 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, thefiles in user home directories are shareable whereas device lock filesare not.
"Static" files include binaries, libraries,documentation files and other files that do not change without systemadministrator intervention. "Variable" files are files that are notstatic.
Shareablefiles can be stored on one host and used on several others. Typically,however, not all files in the filesystem hierarchy are shareable and soeach system has local storage containing at least its unshareablefiles. It is convenient if all the files a system requires that arestored on a foreign host can be made available by mounting one or a fewdirectories from the foreign host.
Static and variable filesshould be segregated because static files, unlike variable files, canbe stored on read-only media and do not need to be backed up on thesame 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.)
Chapter 3. The Root Filesystem
Purpose
The contents of the root filesystem must be adequate to boot, restore, recover, and/or repair the system.
Toboot a system, enough must be present on the root partition to mountother filesystems. This includes utilities, configuration, boot loaderinformation, and other essential start-up data. /usr, /opt, and /var are designed such that they may be located on other partitions or filesystems.
Toenable recovery and/or repair of a system, those utilities needed by anexperienced maintainer to diagnose and reconstruct a damaged systemmust be present on the root filesystem.
Torestore a system, those utilities needed to restore from system backups(on floppy, tape, etc.) must be present on the root filesystem.
Theprimary concern used to balance these considerations, which favorplacing many things on the root filesystem, is the goal of keeping rootas small as reasonably possible. For several reasons, it is desirableto keep the root filesystem small:
It is occasionally mounted from very small media.
Theroot filesystem contains many system-specific configuration files.Possible examples include a kernel that is specific to the system, aspecific hostname, etc. This means that the root filesystem isn'talways shareable between networked systems. Keeping it small on serversin networked systems minimizes the amount of lost space for areas ofunshareable files. It also allows workstations with smaller local harddrives.
While you may have the root filesystem on alarge partition, and may be able to fill it to your heart's content,there will be people with smaller partitions. If you have more filesinstalled, you may find incompatibilities with other systems using rootfilesystems on smaller partitions. If you are a developer then you maybe turning your assumption into a problem for a large number of users.
Diskerrors that corrupt data on the root filesystem are a greater problemthan errors on any other partition. A small root filesystem is lessprone to corruption as the result of a system crash.
Applicationsmust never create or require special files or subdirectories in theroot directory. Other locations in the FHS hierarchy provide more thanenough flexibility for any package.
There are several reasons why creating a new subdirectory of the root filesystem is prohibited:
Itdemands space on a root partition which the system administrator maywant kept small and simple for either performance or security reasons.
Itevades whatever discipline the system administrator may have set up fordistributing standard file hierarchies across mountable volumes.
Distributionsshould not create new directories in the root hierarchy withoutextremely careful consideration of the consequences including forapplication portability.
Requirements
The following directories, or symbolic links to directories, are required in /.
Each directory listed above is specified in detail in separate subsections below. /usr and /var each have a complete section in this document due to the complexity of those directories.
Specific Options
The following directories, or symbolic links to directories, must be in /, if the corresponding subsystem is installed:
Each directory listed above is specified in detail in separate subsections below.
/bin : Essential user command binaries (for use by all users)
Purpose
/bincontains commands that may be used by both the system administrator andby users, but which are required when no other filesystems are mounted(e.g. in single user mode). It may also contain commands which are usedindirectly by scripts. [1]
Requirements
There must be no subdirectories in /bin.
The following commands, or symbolic links to commands, are required in /bin.
If /bin/sh is not a true Bourne shell, 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.
For example bash behaves differently when called as sh or bash. The use of a symbolic link also allows users to easily see that /bin/sh is not a true Bourne shell.
The requirement for the [ and test commands to be included as binaries (even if implemented internally by the shell) is shared with the POSIX.2 standard.
Specific Options
The following programs, or symbolic links to programs, must be in /bin if the corresponding subsystem is installed:
If the gunzip and zcat programs exist, they must be symbolic or hard links to gzip. /bin/csh may be a symbolic link to /bin/tcsh or /usr/bin/tcsh.
The tar, gzip and cpio commands have been added to make restoration of a system possible (provided that / is intact).
Conversely,if no restoration from the root partition is ever expected, then thesebinaries 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.
/boot : Static files of the boot loader
Purpose
Thisdirectory contains everything required for the boot process exceptconfiguration files not needed at boot time and the map installer. Thus/boot stores data that is used before the kernel begins executinguser-mode programs. This may include saved master boot sectors andsector map files. [2]
Specific Options
The operating system kernel must be located in either / or /boot. [3]
/dev : Device files
Purpose
The /dev directory is the location of special or device files.
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, MAKEDEVmust have provisions for creating any device that may be found on thesystem, not just those that a particular implementation installs.
/etc : Host-specific system configuration
Purpose
The /etchierarchy contains configuration files. A "configuration file" is alocal file used to control the operation of a program; it must bestatic and cannot be an executable binary. [4]
Requirements
No binaries may be located under /etc. [5]
The following directories, or symbolic links to directories are required in /etc:
Specific Options
The following directories, or symbolic links to directories must be in /etc, if the corresponding subsystem is installed:
The following files, or symbolic links to files, must be in /etc if the corresponding subsystem is installed: [6]
mtab does not fit the static nature of /etc: it is excepted for historical reasons. [7]
/etc/opt : Configuration files for /opt
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.
Requirements
No structure is imposed on the internal arrangement of /etc/opt/<subdir>.
Ifa configuration file must reside in a different location in order forthe package or system to function properly, it may be placed in alocation other than /etc/opt/<subdir>.
Refer to the rationale for /opt.
/etc/X11 : Configuration for the X Window System (optional)
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.
Specific Options
The following files, or symbolic links to files, must be in /etc/X11 if the corresponding subsystem is installed:
Subdirectories of /etc/X11 may include those for xdm and for any other programs (some window managers, for example) that need them. [8] We recommend that window managers with only one configuration file which is a default .*wmrc file must name it system.*wmrc(unless there is a widely-accepted alternative name) and not use asubdirectory. Any window manager subdirectories must be identicallynamed to the actual window manager binary.
/etc/sgml : Configuration files for SGML (optional)
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 *.catare the DTD-specific centralized catalogs, containing references to allother catalogs needed to use the given DTD. The super catalog file catalog references all the centralized catalogs.
/etc/xml : Configuration files for XML (optional)
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.
/home : User home directories (optional)
Purpose
/home is a fairly standard concept, but it is clearly a site-specific filesystem. [9] The setup will differ from host to host. Therefore, no program should rely on this location. [10]
Requirements
Userspecific configuration files for applications are stored in the user'shome directory in a file that starts with the '.' character (a "dotfile"). If an application needs to create more than one dot file thenthey should be placed in a subdirectory with a name starting with a '.'character, (a "dot directory"). In this case the configuration filesshould not start with the '.' character. [11]
/lib : Essential shared libraries and kernel modules
Purpose
The /libdirectory contains those shared library images needed to boot thesystem and run the commands in the root filesystem, ie. by binaries in /bin and /sbin. [12]
Requirements
At least one of each of the following filename patterns are required (they may be files, or symbolic links):
If a C preprocessor is installed, /lib/cpp must be a reference to it, for historical reasons. [13]
Specific Options
The following directories, or symbolic links to directories, must be in /lib, if the corresponding subsystem is installed:
/lib<qual> : Alternate format essential shared libraries (optional)
Purpose
There may be one or more variants of the /lib directory on systems which support more than one binary format requiring separate libraries. [14]
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. [15]
/media : Mount point for removeable media
Purpose
Thisdirectory contains subdirectories which are used as mount points forremoveable media such as floppy disks, cdroms and zip disks.
Historically there have been a number of other different places used to mount removeable media such as /cdrom, /mnt or /mnt/cdrom.Placing the mount points for all removeable media directly in the rootdirectory would potentially result in a large number of extradirectories 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.
Specific Options
The following directories, or symbolic links to directories, must be in /media, if the corresponding subsystem is installed:
Onsystems where more than one device exists for mounting a certain typeof media, mount directories can be created by appending a digit to thename of those available above starting with '0', but the unqualifiedname must also exist. [16]
/mnt : Mount point for a temporarily mounted filesystem
Purpose
Thisdirectory is provided so that the system administrator may temporarilymount a filesystem as needed. The content of this directory is a localissue and should not affect the manner in which any program is run.
Thisdirectory must not be used by installation programs: a suitabletemporary directory not in use by the system must be used instead.
/opt : Add-on application software packages
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.
Requirements
The directories /opt/bin, /opt/doc, /opt/include, /opt/info, /opt/lib, and /opt/manare 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 mustfunction 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/opthierarchies except for those package files that must reside in specificlocations within the filesystem tree in order to function properly. Forexample, device lock files must be placed in /var/lock and devices must be located in /dev.
Distributions may install software in /opt,but must not modify or delete software installed by the local systemadministrator without the assent of the local system administrator.
The use of /optfor add-on software is a well-established practice in the UNIXcommunity. The System V Application Binary Interface [AT&T 1990],based on the System V Interface Definition (Third Edition), providesfor 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 /optare necessary because conflicts are possible betweendistribution-installed and locally-installed software, especially inthe 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.
/root : Home directory for the root user (optional)
Purpose
Theroot account's home directory may be determined by developer or localpreference, but this is the recommended default location. [17]
/sbin : System binaries
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]
Requirements
The following commands, or symbolic links to commands, are required in /sbin.
Specific Options
The following files, or symbolic links to files, must be in /sbin if the corresponding subsystem is installed:
/srv : Data for services provided by this system
Purpose
/srv contains site-specific data which is served by this system.
Thismain purpose of specifying this is so that users may find the locationof the data files for particular service, and so that services whichrequire a single tree for readonly data, writable data and scripts(such as cgi scripts) can be reasonably placed. Data that is only ofinterest to a specific user should go in that users' home directory.
The methodology used to name subdirectories of /srv is unspecified as there is currently no consensus on how this should be done. One method for structuring data under /srv is by protocol, eg. ftp, rsync, www, and cvs. On large systems it can be useful to structure /srv by administrative context, such as /srv/physics/www, /srv/compsci/cvs, etc. This setup will differ from host to host. Therefore, no program should rely on a specific subdirectory structure of /srv existing or data necessarily being stored in /srv. However /srv should always exist on FHS compliant systems and should be used as the default location for such data.
Distributions must take care not to remove locally placed files in these directories without administrator permission. [20]
/tmp : Temporary files
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.
IEEE standard P1003.2 (POSIX, part 2) makes requirements that are 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.
FHSadded this recommendation on the basis of historical precedent andcommon practice, but did not make it a requirement because systemadministration is not within the scope of this standard.
Chapter 4. The /usr Hierarchy
Purpose
/usr is the second major section of the filesystem. /usr is shareable, read-only data. That means that /usrshould be shareable between various FHS-compliant hosts and must not bewritten to. Any information that is host-specific or varies with timeis stored elsewhere.
Large software packages must not use a direct subdirectory under the /usr hierarchy.
Requirements
The following directories, or symbolic links to directories, are required in /usr.
Specific Options
An exception is made for the X Window System because of considerable precedent and widely-accepted practice.
Thefollowing symbolic links to directories may be present. Thispossibility is based on the need to preserve compatibility with oldersystems until all implementations 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.
/usr/X11R6 : X Window System, Version 11 Release 6 (optional)
Purpose
This hierarchy is reserved for the X Window System, version 11 release 6, and related files.
Tosimplify matters and make XFree86 more compatible with the X WindowSystem on other systems, the following symbolic links must be presentif /usr/X11R6 exists:
/usr/bin/X11 -> /usr/X11R6/bin
/usr/lib/X11 -> /usr/X11R6/lib/X11
/usr/include/X11 -> /usr/X11R6/include/X11
Ingeneral, software must not be installed or managed via the abovesymbolic links. They are intended for utilization by users only. Thedifficulty is related to the release version of the X Window System —in transitional periods, it is impossible to know what release of X11is in use.
Specific Options
Host-specific data in /usr/X11R6/lib/X11should be interpreted as a demonstration file. Applications requiringinformation about the current host must reference a configuration filein /etc/X11, which may be linked to a file in /usr/X11R6/lib. [21]
/usr/bin : Most user commands
Purpose
This is the primary directory of executable commands on the system.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/bin, if the corresponding subsystem is installed:
/usr/bin/X11 must be a symlink to /usr/X11R6/bin if the latter exists.
The following files, or symbolic links to files, must be in /usr/bin, if the corresponding subsystem is installed:
Because shell script interpreters (invoked with #!<path>on the first line of a shell script) cannot rely on a path, it isadvantageous to standardize their locations. The Bourne shell andC-shell interpreters are already fixed in /bin,but Perl, Python, and Tcl are often found in many different places.They may be symlinks to the physical location of the shellinterpreters.
/usr/include : Directory for standard include files.
Purpose
This is where all of the system's general-use include files for the C programming language should be placed.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/include, if the corresponding subsystem is installed:
The symbolic link /usr/include/X11 must link to /usr/X11R6/include/X11 if the latter exists.
/usr/lib : Libraries for programming and packages
Purpose
/usr/libincludes object files, libraries, and internal binaries that are notintended 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 dataexclusively used by the application must be placed within thatsubdirectory. [23]
Specific Options
For historical reasons, /usr/lib/sendmail must be a symbolic link to /usr/sbin/sendmail if the latter exists. [24]
If /lib/X11 exists, /usr/lib/X11 must be a symbolic link to /lib/X11, or to whatever /lib/X11 is a symbolic link to. [25]
/usr/lib<qual> : Alternate format libraries (optional)
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. [26]
/usr/local : Local hierarchy
Purpose
The /usr/localhierarchy is for use by the system administrator when installingsoftware locally. It needs to be safe from being overwritten when thesystem software is updated. It may be used for programs and data thatare 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. [27]
Requirements
The following directories, or symbolic links to directories, must be in /usr/local
No other directories, except those listed below, may be in /usr/local after first installing a FHS-compliant system.
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.
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 alltheir configuration under one hierarchy.
Note that /usr/etc is still not allowed: programs in /usr should place configuration files in /etc.
/usr/local/share
The requirements for the contents of this directory are the same as /usr/share. The only additional constraint is that /usr/local/share/man and /usr/local/man directories must be synonomous (usually this means that one of them must be a symbolic link). [28]
/usr/sbin : Non-essential standard system binaries
Purpose
Thisdirectory contains any non-essential binaries used exclusively by thesystem administrator. System administration programs that are requiredfor system repair, system recovery, mounting /usr, or other essential functions must be placed in /sbin instead. [29]
/usr/share : Architecture-independent data
Purpose
The /usr/share hierarchy is for all read-only architecture independent data files. [30]
Thishierarchy is intended to be shareable among all architecture platformsof a given OS; thus, for example, a site with i386, Alpha, and PPCplatforms 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.
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.
Requirements
The following directories, or symbolic links to directories, must be in /usr/share
Specific Options
The following directories, or symbolic links to directories, must be in /usr/share, if the corresponding subsystem is installed:
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.
/usr/share/dict : Word lists (optional)
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.
The reason that only word lists are located here is that they are the only files common to all spell checkers.
Specific Options
The following files, or symbolic links to files, must be in /usr/share/dict, if the corresponding subsystem is installed:
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 an ISO 8859 character set which isappropriate for the language in question; if possible the Latin1 (ISO8859-1) character set should be used (this is often not possible).
Other word lists must be included here, if present.
/usr/share/man : Manual pages
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 commandsare contained in this chapter. Most program documentation that a userwill 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 libraryroutines that are not direct calls to kernel services. This and chapter2 are only really of interest to programmers.
man4:Special files Section 4 describes the special files, related driverfunctions, 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 thesection 5. This includes various include files, program output files,and system files.
man6:Games This chapter documents games, demos, and generally trivialprograms. Different people have various notions about how essentialthis is.
man7:Miscellaneous Manual pages that are difficult to classify aredesignated as being section 7. The troff and other text processingmacro packages are found here.
man8:System administration Programs used by system administrators for systemoperation and maintenance are documented here. Some of these programsare also occasionally useful for normal users.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/share/<mandir>/<locale>, unless they are empty: [32]
The component <section> describes the manual section.
Provisions must be made in the structure of /usr/share/manto support manual pages which are written in different (or multiple)languages. These provisions must take into account the storage andreference of these manual pages. Relevant factors include language(including geographical-based differences), and character code set.
This naming of language subdirectories of /usr/share/manis based on Appendix E of the POSIX 1003.1 standard which describes thelocale identification string — the most well-accepted method todescribe 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 ofnames of languages). It must be two characters wide and specified withlowercase letters only.
The <territory>field must be the two-letter code of ISO 3166 (a specification ofrepresentations of countries), if possible. (Most people are familiarwith the two-letter codes used for the country codes in emailaddresses.) It must be two characters wide and specified with uppercaseletters 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 numberof the international standard describing the character set. It isrecommended that this be a numeric representation if possible (ISOstandards, especially), not include additional punctuation symbols, andthat 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 betweendifferent cultural needs; for instance, dictionary order versus a moresystems-oriented collating order. This standard recommends not usingthe <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:
Similarly,provision must be made for manual pages which arearchitecture-dependent, such as documentation on device-drivers orlow-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. Manual pages for X11R6 are stored in /usr/X11R6/man. It follows that all manual page hierarchies in the system must have the same structure as /usr/share/man.
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.
Thenumbered sections "1" through "8" are traditionally defined. Ingeneral, the file name for manual pages located within a particularsection end with .<section>.
Inaddition, some large sets of application-specific manual pages have anadditional 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 and /usr/X11R6/man. (This portion of the standard also applies later in the section on the optional /var/cache/man structure.)
/usr/share/misc : Miscellaneous architecture-independent data
This directory contains miscellaneous architecture-independent files which don't require a separate subdirectory under /usr/share.
Specific Options
The following files, or symbolic links to files, must be in /usr/share/misc, if the corresponding subsystem is installed:
Other (application-specific) files may appear here, but a distributor may place them in /usr/lib at their discretion. [34]
/usr/share/sgml : SGML data (optional)
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.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/share/sgml, if the corresponding subsystem is installed:
Other files that are not specific to a given DTD may reside in their own subdirectory.
/usr/share/xml : XML data (optional)
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.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/share/xml, if the corresponding subsystem is installed:
/usr/src : Source code (optional)
Purpose
Source code may be place placed in this subdirectory, only for reference purposes. [35]
Chapter 5. The /var Hierarchy
Purpose
/varcontains variable data files. This includes spool directories andfiles, administrative and logging data, and transient and temporaryfiles.
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 /usrpartition. (This is sometimes done to reduce the size of the rootpartition 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-wideimplication, and in consultation with the FHS mailing list.
Requirements
The following directories, or symbolic links to directories, are required in /var.
Severaldirectories are `reserved' in the sense that they must not be usedarbitrarily by some new application, since they would conflict withhistorical and/or local practice. They are:
/var/backups
/var/cron
/var/msgs
/var/preserve
Specific Options
The following directories, or symbolic links to directories, must be in /var, if the corresponding subsystem is installed:
/var/account : Process accounting logs (optional)
Purpose
Thisdirectory holds the current active process accounting log and thecomposite process usage data (as used in some UNIX-like systems by lastcomm and sa).
/var/cache : Application cache data
Purpose
/var/cacheis intended for cached data from applications. Such data is locallygenerated as a result of time-consuming I/O or calculation. Theapplication must be able to regenerate or restore the data. Unlike /var/spool,the cached files can be deleted without data loss. The data must remainvalid between invocations of the application and rebooting the system.
Files located under /var/cachemay be expired in an application specific manner, by the systemadministrator, or both. The application must always be able to recoverfrom manual deletion of these files (generally because of a disk spaceshortage). No other requirements are made on the data format of thecache directories.
Theexistence of a separate directory for cached data allows systemadministrators to set different disk and backup policies from otherdirectories in /var.
Specific Options
/var/cache/fonts : Locally-generated fonts (optional)
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. [36]
Specific Options
Other dynamically created fonts may also be placed in this tree, under appropriately-named subdirectories of /var/cache/fonts.
/var/cache/man : Locally-formatted manual pages (optional)
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.) [37]
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.
Ifpreformatted manual pages come with a system on read-only media (aCD-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.
Release 1.2 of the 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.
/var/crash : System crash dumps (optional)
Purpose
Thisdirectory holds system crash dumps. As of the date of this release ofthe standard, system crash dumps were not supported under Linux but maybe supported by other systems which may comply with the FHS.
/var/games : Variable game data (optional)
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.
/var/games has been given a hierarchy of its own, rather than leaving it merged in with the old /var/libas in release 1.2. The separation allows local control of backupstrategies, permissions, and disk usage, as well as allowing inter-hostsharing and reducing clutter in /var/lib. Additionally, /var/games is the path traditionally used by BSD.
/var/lib : Variable state information
Purpose
Thishierarchy holds state information pertaining to an application or thesystem. State information is data that programs modify while they run,and that pertains to one specific host. Users must never need to modifyfiles in /var/lib to configure a package's operation.
Stateinformation is generally used to preserve the condition of anapplication (or a group of inter-related applications) betweeninvocations and between different instances of the same application.State information should generally remain valid after a reboot, shouldnot 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; theother subdirectories should only be present if the application inquestion is included in the distribution. [38]
/var/lib/<name>is the location that must be used for all distribution packagingsupport. Different distributions may use different names, of course.
Requirements
The following directories, or symbolic links to directories, are required in /var/lib:
Specific Options
The following directories, or symbolic links to directories, must be in /var/lib, if the corresponding subsystem is installed:
/var/lib/<editor> : Editor backup files and state (optional)
Purpose
These directories contain saved files generated by any unexpected termination of an editor (e.g., elvis, jove, nvi).
Othereditors may not require a directory for crash-recovery files, but mayrequire a well-defined place to store other information while theeditor is running. This information should be stored in a subdirectoryunder /var/lib (for example, GNU Emacs would place lock files in /var/lib/emacs/lock).
Futureeditors may require additional state information beyond crash-recoveryfiles and lock files — this information should also be placed under /var/lib/<editor>.
Previous Linux releases, as well as all commercial vendors, use /var/preservefor vi or its clones. However, each editor uses its own format forthese crash-recovery files, so a separate directory is needed for eacheditor.
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.
/var/lib/hwclock : State directory for hwclock (optional)
Purpose
This directory contains the file /var/lib/hwclock/adjtime.
In FHS 2.1, this file was /etc/adjtime, but as hwclock updates it, that was obviously incorrect.
/var/lib/misc : Miscellaneous variable data
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. [39]
/var/lock : Lock files
Purpose
Lock files should be stored within the /var/lock directory structure.
Lockfiles for devices and other resources shared by multiple applications,such as the serial device lock files that were originally found ineither /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 thebase name of the device. For example, to lock /dev/ttyS0 the file"LCK..ttyS0" would be created. [40]
Theformat used for the contents of such lock files must be the HDB UUCPlock file format. The HDB format is to store the process identifier(PID) as a ten byte ASCII decimal number, with a trailing newline. Forexample, if process 1230 holds a lock file, it would contain the elevencharacters: space, space, space, space, space, space, one, two, three,zero, and newline.
/var/log : Log files and directories
Purpose
This directory contains miscellaneous log files. Most logs must be written to this directory or an appropriate subdirectory.
Specific Options
The following files, or symbolic links to files, must be in /var/log, if the corresponding subsystem is installed:
/var/mail : User mailbox files (optional)
Purpose
The mail spool must be accessible through /var/mail and the mail spool files must take the form <username>. [41]
User mailbox files in this location must be stored in the standard UNIX mailbox format.
The logical location for this directory was changed from /var/spool/mailin order to bring FHS in-line with nearly every UNIX implementation.This change is important for inter-operability since a single /var/mail is often shared between multiple hosts and multiple UNIX implementations (despite NFS locking issues).
Itis important to note that there is no requirement to physically movethe mail spool to this location. However, programs and header filesmust be changed to use /var/mail.
/var/opt : Variable data for /opt
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>.
Refer to the rationale for /opt.
/var/run : Run-time variable data
Purpose
Thisdirectory contains system information data describing the system sinceit was booted. Files under this directory must be cleared (removed ortruncated as appropriate) at the beginning of the boot process.Programs may have a subdirectory of /var/run; this is encouraged for programs that use more than one run-time file. [42] Process identifier (PID) files, which were originally placed in /etc, must be placed in /var/run. The naming convention for PID files is <program-name>.pid. For example, the crond PID file is named /var/run/crond.pid.
Requirements
Theinternal format of PID files remains unchanged. The file must consistof the process identifier in ASCII-encoded decimal, followed by anewline character. For example, if crond was process number 25, /var/run/crond.pid would contain three characters: two, five, and newline.
Programsthat read PID files should be somewhat flexible in what they accept;i.e., they should ignore extra whitespace, leading zeroes, absence ofthe trailing newline, or additional lines in the PID file. Programsthat create PID files should use the simple specification located inthe above paragraph.
The utmp file, which stores information about who is currently using the system, is located in this directory.
System programs that maintain transient UNIX-domain sockets must place them in this directory.
/var/spool : Application spool data
Purpose
/var/spool contains data which is awaiting some kind of later processing. Data in /var/spoolrepresents work to be done in the future (by a program, user, oradministrator); often data is deleted after it has been processed. [43]
Specific Options
The following directories, or symbolic links to directories, must be in /var/spool, if the corresponding subsystem is installed:
/var/spool/lpd : Line-printer daemon print queues (optional)
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.
Specific Options
/var/spool/rwho : Rwhod files (optional)
Purpose
This directory holds the rwhod information for other systems on the local net.
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.
/var/tmp : Temporary files preserved between system reboots
Purpose
The /var/tmpdirectory is made available for programs that require temporary filesor 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.
/var/yp : Network Information Service (NIS) database files (optional)
Purpose
Variabledata for the Network Information Service (NIS), formerly known as theSun Yellow Pages (YP), must be placed in this directory.
/var/yp is the standard directory for NIS (YP) data and is almost exclusively used in NIS documentation and systems. [44]
Chapter 6. Operating System Specific Annex
Thissection is for additional requirements and recommendations that onlyapply to a specific operating system. The material in this sectionshould never conflict with the base standard.
Linux
This is the annex for the Linux operating system.
/ : 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.
/bin : Essential user command binaries (for use by all users)
Linux systems which require them place these additional files into /bin:
setserial
/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
Thisdevice is a source of zeroed out data. All data written to this deviceis discarded. A read from this device will return as many bytescontaining the value zero as was requested.
- /dev/tty
Thisdevice is a synonym for the controlling terminal of a process. Oncethis device is opened, all reads and writes will behave as if theactual controlling terminal device had been opened.
Previous versions of the FHS had stricter requirements for /dev.Other devices may also exist in /dev. Device names may exist assymbolic links to other device nodes located in /dev or subdirectoriesof /dev. There is no requirement concerning major/minor number values.
/etc : Host-specific system configuration
Linux systems which require them place these additional files into /etc.
lilo.conf
/lib64 and /lib32 : 64/32-bit libraries (architecture dependent)
The 64-bit architectures PPC64, s390x, sparc64 and AMD64 must place 64-bit libraries in /lib64, and 32-bit (or 31-bit on s390) libraries in /lib.
The 64-bit architecture IA64 must place 64-bit libraries in /lib.
This is a refinement of the general rules for /lib<qual> and /usr/lib<qual>.The architectures PPC64, s390x, sparc64 and AMD64 support support both32-bit (for s390 more precise 31-bit) and 64-bit programs. Using libfor 32-bit binaries allows existing binaries from the 32-bit systems towork without any changes: such binaries are expected to be numerous.IA-64 uses a different scheme, reflecting the deprecation of 32-bitbinaries (and hence libraries) on that architecture.
/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/kmemand other similar methods. We strongly encourage this for the storageand retrieval of process information as well as other kernel and memoryinformation.
/sbin : Essential system binaries
Linux systems place these additional files into /sbin.
Second extended filesystem commands (optional):
badblocks
dumpe2fs
e2fsck
mke2fs
mklost+found
tune2fs
Boot-loader map installer (optional):
lilo
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:
I've just removed /lib/<file>.
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.
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.
Sincethe default action in the kernel for the Ctrl-Alt-Del key combinationis an instant hard reboot, it is generally advisable to disable thebehavior 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.
/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
/usr/src : Source code
Forsystems based on glibc, there are no specific guidelines for thisdirectory. 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.
Ifa C or C++ compiler is installed, but the complete Linux kernel sourcecode is not installed, then the include files from the kernel sourcecode 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.
/usr/src/linux may be a symbolic link to a kernel source code tree.
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.
/var/spool/cron : cron and at jobs
This directory contains the variable data for the cron and at programs.
Chapter 7. Appendix
The FHS mailing list
TheFHS mailing list is located at<freestandards-fhs-discuss@lists.sourceforge.net>. You cansubscribe to the mailing list at this page http://sourceforge.net/projects/freestandards/.
Thanksto Network Operations at the University of California at San Diego whoallowed us to use their excellent mailing list server.
As notedin the introduction, please do not send mail to the mailing listwithout first contacting the FHS editor or a listed contributor.
Background of the FHS
Theprocess of developing a standard filesystem hierarchy began in August1993 with an effort to restructure the file and directory structure ofLinux. The FSSTND, a filesystem hierarchy standard specific to theLinux operating system, was released on February 14, 1994. Subsequentrevisions were released on October 9, 1994 and March 28, 1995.
Inearly 1995, the goal of developing a more comprehensive version ofFSSTND to address not only Linux, but other UNIX-like systems wasadopted with the help of members of the BSD development community. As aresult, a concerted effort was made to focus on issues that weregeneral to UNIX-like systems. In recognition of this widening of scope,the name of the standard was changed to Filesystem Hierarchy Standardor FHS for short.
Volunteers who have contributed extensively tothis standard are listed at the end of this document. This standardrepresents a consensus view of those and other contributors.
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.
Gainthe approval of distributors, developers, and other decision-makers inrelevant development groups and encourage their participation.
Provide a standard that is attractive to the implementors of different UNIX-like systems.
Scope
Thisdocument specifies a standard filesystem hierarchy for FHS filesystemsby specifying the location of files and directories, and the contentsof some system files.
This standard has been designed to be usedby system integrators, package developers, and system administrators inthe construction and maintenance of FHS compliant filesystems. It isprimarily intended to be a reference and is not a tutorial on how tomanage a conforming filesystem hierarchy.
The FHS grew out ofearlier work on FSSTND, a filesystem organization standard for theLinux operating system. It builds on FSSTND to address interoperabilityissues not just in the Linux community but in a wider arena including4.4BSD-based operating systems. It incorporates lessons learned in theBSD world and elsewhere about multi-architecture support and thedemands of heterogeneous networking.
Although this standard ismore comprehensive than previous attempts at filesystem hierarchystandardization, periodic updates may become necessary as requirementschange in relation to emerging technology. It is also possible thatbetter solutions to the problems addressed here will be discovered sothat our solutions will no longer be the best possible solutions.Supplementary drafts may be released in addition to periodic updates tothis document. However, a specific goal is backwards compatibility fromone release of this document to the next.
Comments related tothis standard are welcome. Any comments or suggestions for changes maybe directed to the FHS editor (Daniel Quinlan<quinlan@pathname.com>) or the FHS mailing list. Typographical orgrammatical comments should be directed to the FHS editor.
Beforesending mail to the mailing list it is requested that you first contactthe FHS editor in order to avoid excessive re-discussion of old topics.
Questionsabout how to interpret items in this document may occasionally arise.If you have need for a clarification, please contact the FHS editor.Since this standard represents a consensus of many participants, it isimportant to make certain that any interpretation also represents theircollective opinion. For this reason it may not be possible to providean immediate response unless the inquiry has been the subject ofprevious discussion.
Acknowledgments
Thedevelopers of the FHS wish to thank the developers, systemadministrators, 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 thankthose Linux developers who supported the FSSTND, the predecessor tothis standard. If they hadn't demonstrated that the FSSTND wasbeneficial, the FHS could never have evolved.
Contributors
Notes
[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]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 must be placed in /etc.
The GRUB bootloader reads its configurations file before booting, so that must be placed in /boot. However, it is a configuration file, so should be in /etc. The answer here is a symbolic link such as /etc/grub/menu.lst -> /boot/menu.lst.
[3]On some i386 machines, it may be necessary for /boot to be located on a separate partition located completely below cylinder 1024 of the boot device due to hardware constraints.
Certain MIPS systems require a /bootpartition that is a mounted MS-DOS filesystem or whatever otherfilesystem type is accessible for the firmware. This may result inrestrictions with respect to usable filenames within /boot (only for affected systems).
[4]Thesetup of command scripts invoked at boot time may resemble System V,BSD or other models. Further specification in this area may be added toa future version of this standard.
[5]It is recommended that files be stored in subdirectories of /etc rather than directly in /etc.
[6]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).
[7]On some Linux systems, this may be a symbolic link to /proc/mounts, in which case this exception is not required.
[8]/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.
[9]Differentpeople prefer to place user accounts in a variety of places. Thissection describes only a suggested placement for user home directories;nevertheless we recommend that all FHS-compliant distributions use thisas the default location for home directories.
On small systems, each user's directory is typically one of the many subdirectories of /home such as /home/smith, /home/torvalds, /home/operator, etc. On large systems (especially when the /homedirectories are shared amongst many hosts using NFS) it is useful tosubdivide user home directories. Subdivision may be accomplished byusing subdirectories such as /home/staff, /home/guests, /home/students, etc.
[10]If you want to find out a user's home directory, you should use the getpwent(3) library function rather than relying on /etc/passwd because user information may be stored remotely using systems such as NIS.
[11]Itis recommended that apart from autosave and lock files programs shouldrefrain from creating non dot files or directories in a home directorywithout user intervention.
[12]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.
[13]The usual placement of this binary is /usr/bin/cpp.
[14]Thisis commonly used for 64-bit or 32-bit support on systems which supportmultiple binary formats, but require libraries of the same name. Inthis case, /lib32 and /lib64 might be the library directories, and /lib a symlink to one of them.
[15]/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).
[16]A compliant implementation with two CDROM drives might have /media/cdrom0 and /media/cdrom1 with /media/cdrom a symlink to either of these.
[17]Ifthe home directory of the root account is not stored on the rootpartition it will be necessary to make certain it will default to / if it can not be located.
Werecommend against using the root account for tasks that can beperformed as an unprivileged user, and that it be used solely forsystem administration. For this reason, we recommend thatsubdirectories for mail and other applications not appear in the rootaccount's home directory, and that mail for administration roles suchas root, postmaster, and webmaster be forwarded to an appropriate user.
[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) userwill 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 /sbinwas not created for security reasons or to prevent users from seeingthe operating system, but to provide a good partition between binariesthat everyone uses and ones that are primarily used for administrationtasks. There is no inherent security advantage in making /sbin off-limits for users.
[20]Thisis particularly important as these areas will often contain both filesinitially installed by the distributor, and those added by theadministrator.
[21]Examples of such configuration files include Xconfig, XF86Config, or system.twmrc)
[22]Miscellaneous architecture-independent application-specific static files and subdirectories must be placed in /usr/share.
[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 a symbolic link 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 Xconfig or XF86Config 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/X11R6/lib/X11).
[26]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.
[27]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.
[28]/usr/local/man may be deprecated in future FHS releases, so if all else is equal, making that one a symlink seems sensible.
[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/local/man has no manual pages in section 4 (Devices), then /usr/local/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]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
[35]Generally, source should not be built within this hierarchy.
[36]Thisstandard does not currently incorporate the TeX Directory Structure (adocument that describes the layout TeX files and directories), but itmay be useful reading. It is located at ftp://ctan.tug.org/tex/
[37]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.
[38]Animportant difference between this version of this standard and previousones is that applications are now required to use a subdirectory of /var/lib.
[39]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).
[40]Then, anything wishing to use /dev/ttyS0 can read the lock file and act accordingly (all locks in /var/lock should be world-readable).
[41]Note that /var/mail may be a symbolic link to another directory.
[42]/var/runshould be unwritable for unprivileged users (root or users runningdaemons); it is a major security problem if any user can write in thisdirectory.
[43]UUCP lock files must be placed in /var/lock. See the above section on /var/lock.
[44]NIS should not be confused with Sun NIS+, which uses a different directory, /var/nis.
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