Filesystem Hierarchy Standard
| Developed by | Linux Foundation |
|---|---|
| Initial release | 14 February 1994 (1994-02-14) |
| Latest release | 3.0 (3 June 2015 (2015-06-03)) |
| Website | Official website Official website (Historical) |
The Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Linux distributions.[1] It is maintained by the Linux Foundation. The latest version is 3.0, released on 3 June 2015.[2]
Contents
1 Directory structure
2 FHS compliance
3 History
3.1 Release history
4 See also
5 References
6 External links
Directory structure
In the FHS, all files and directories appear under the root directory /, even if they are stored on different physical or virtual devices. Some of these directories only exist on a particular system if certain subsystems, such as the X Window System, are installed.
Most of these directories exist in all Unix-like operating systems and are generally used in much the same way; however, the descriptions here are those used specifically for the FHS, and are not considered authoritative for platforms other than Linux.
| Directory | Description |
|---|---|
| Primary hierarchy root and root directory of the entire file system hierarchy. |
| Essential command binaries that need to be available in single user mode; for all users, e.g., cat, ls, cp. |
| Boot loader files, e.g., kernels, initrd. |
| device files, e.g., /dev/null, /dev/disk0, /dev/sda1, /dev/tty, /dev/random. |
| Host-specific system-wide configuration files There has been controversy over the meaning of the name itself. In early versions of the UNIX Implementation Document from Bell labs, |
| Configuration files for add-on packages that are stored in /opt. |
| Configuration files, such as catalogs, for software that processes SGML. |
| Configuration files for the X Window System, version 11. |
| Configuration files, such as catalogs, for software that processes XML. |
| Users' home directories, containing saved files, personal settings, etc. |
| Libraries essential for the binaries in /bin and /sbin. |
| Alternative format essential libraries. Such directories are optional, but if they exist, they have some requirements. |
| Mount points for removable media such as CD-ROMs (appeared in FHS-2.3 in 2004). |
| Temporarily mounted filesystems. |
| Optional application software packages.[6] |
| Virtual filesystem providing process and kernel information as files. In Linux, corresponds to a procfs mount. Generally automatically generated and populated by the system, on the fly. |
| Home directory for the root user. |
| Run-time variable data: Information about the running system since last boot, e.g., currently logged-in users and running daemons. Files under this directory must be either removed or truncated at the beginning of the boot process; but this is not necessary on systems that provide this directory as a temporary filesystem (tmpfs). |
| Essential system binaries, e.g., fsck, init, route. |
| Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems (appeared in FHS-2.3 in 2004). |
| Contains information about devices, drivers, and some kernel features.[7] |
| Temporary files (see also /var/tmp). Often not preserved between system reboots, and may be severely size restricted. |
| Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.[8] |
| Non-essential command binaries (not needed in single user mode); for all users. |
| Standard include files. |
| Libraries for the binaries in /usr/bin and /usr/sbin. |
| Alternative format libraries, e.g. /usr/lib32 for 32-bit libraries on a 64-bit machine (optional). |
| Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, e.g., bin, lib, share.[9] |
| Non-essential system binaries, e.g., daemons for various network-services. |
| Architecture-independent (shared) data. |
| Source code, e.g., the kernel source code with its header files. |
| X Window System, Version 11, Release 6 (up to FHS-2.3, optional). |
| Variable files—files whose content is expected to continually change during normal operation of the system—such as logs, spool files, and temporary e-mail files. |
| Application cache data. Such data are locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. The cached files can be deleted without loss of data. |
| State information. Persistent data modified by programs as they run, e.g., databases, packaging system metadata, etc. |
| Lock files. Files keeping track of resources currently in use. |
| Log files. Various logs. |
| Mailbox files. In some distributions, these files may be located in the deprecated /var/spool/mail. |
| Variable data from add-on packages that are stored in /opt. |
| Run-time variable data. This directory contains system information data describing the system since it was booted.[10] In FHS 3.0, |
| Spool for tasks waiting to be processed, e.g., print queues and outgoing mail queue. |
| Deprecated location for users' mailboxes.[12] |
| Temporary files to be preserved between reboots. |
FHS compliance
Most Linux distributions follow the Filesystem Hierarchy Standard and declare it their own policy to maintain FHS compliance.[13][14][15][16]GoboLinux[17] and NixOS[18] provide examples of intentionally non-compliant filesystem implementations.
Some distributions generally follow the standard but deviate from it in some areas. Common deviations include:
- Modern Linux distributions include a
/sysdirectory as a virtual filesystem (sysfs, comparable to/proc, which is a procfs), which stores and allows modification of the devices connected to the system,[19] whereas many traditional Unix-like operating systems use/sysas a symbolic link to the kernel source tree.[20]
- Many modern Unix-like systems (like FreeBSD via its ports system) install third party packages into
/usr/localwhile keeping code considered part of the operating system in/usr. - Some Linux distributions no longer differentiate between
/libversus/usr/liband have/libsymlinked to/usr/lib.[21]
- Some Linux distributions no longer differentiate between
/binversus/usr/binand/sbinversus/usr/sbin. They may symlink/binto/usr/binand/sbinto/usr/sbin. Other distributions choose to consolidate all four, symlinking them to/usr/bin.[22]
Modern Linux distributions include a /run directory as a temporary filesystem (tmpfs) which stores volatile runtime data, following the FHS version 3.0. According to the FHS version 2.3, such data were stored in /var/run but this was a problem in some cases because this directory is not always available at early boot. As a result, these programs have had to resort to trickery, such as using /dev/.udev, /dev/.mdadm, /dev/.systemd or /dev/.mount directories, even though the device directory isn't intended for such data.[23] Among other advantages, this makes the system easier to use normally with the root filesystem mounted read-only.
For example, below are the changes Debian made in its 2013 Wheezy release:[24]
/dev/.*→/run/*
/dev/shm→/run/shm
/dev/shm/*→/run/*
/etc/*(writeable files) →/run/*
/lib/init/rw→/run
/var/lock→/run/lock
/var/run→/run
/tmp→/run/tmp
History
FHS was created as the FSSTND (short for "Filesystem Standard"[25]), largely based on similar standards for other Unix-like operating systems. Notable examples are these: the hier(7) description of file system layout,[26] which has existed since the release of Version 7 Unix (in 1979); the SunOS filesystem(7)[27] and its successor, the Solaris filesystem(5).[28][29]
Release history
| Version | Release Date | Notes |
|---|---|---|
Old version, no longer supported: 1.0 | 1994-02-14 | FSSTND[30] |
Old version, no longer supported: 1.1 | 1994-10-09 | FSSTND[31] |
Old version, no longer supported: 1.2 | 1995-03-28 | FSSTND[32] |
Old version, no longer supported: 2.0 | 1997-10-26 | FHS 2.0 is the direct successor for FSSTND 1.2. Name of the standard was changed to Filesystem Hierarchy Standard.[33][34][35] |
Old version, no longer supported: 2.1 | 2000-04-12 | FHS[36][37][38] |
Old version, no longer supported: 2.2 | 2001-05-23 | FHS[39] |
Older version, yet still supported: 2.3 | 2004-01-29 | FHS[40] |
Current stable version: 3.0 | 2015-05-18 | FHS[41] |
Legend: Old version Older version, still supported Latest version Latest preview version Future release | ||
See also
- Unix directory structure
Intel Binary Compatibility Standard (iBCS)
– Linux Programmer's Manual – Overview, Conventions and Miscellanea
References
^ "FilesystemHierarchyStandard - Debian Wiki". wiki.debian.org. Retrieved 2016-07-06..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:"""""""'""'"}.mw-parser-output .citation .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .citation .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
^ "FHS 3.0 Released". June 3, 2015.
^ J. DeFelicc (1972-03-17). "E.0". Preliminary Release of UNIX Implementation Document (PDF). p. 8. IMO.1-1.
^ "/etc : Host-specific system configuration". Filesystem Hierarchy Standard. Retrieved 18 February 2016.
^ Define - /etc?, Posted by Cliff, 3 March 2007 - Slashdot
^ "/opt : Add-on application software packages". Filesystem Hierarchy Standard. Retrieved 18 February 2016.
^ "/sys : Kernel and system information virtual filesystem". Filesystem Hierarchy Standard. Retrieved 4 June 2017.
^ Should be shareable and read-only, cf. http://www.pathname.com/fhs/pub/fhs-2.3.html.
^ Historically and strictly according to the standard,/usr/localis for data that must be stored on the local host (as opposed to/usr, which may be mounted across a network). Most of the time/usr/localis used for installing software/data that are not part of the standard operating system distribution (in such case,/usrwould only contain software/data that are part of the standard operating system distribution). It is possible that the FHS standard may in the future be changed to reflect this de facto convention.
^ "Filesystem Hierarchy Standard". FHS 2.3. Section /var/run : Run-time variable data.
^ "5.13. /var/run : Run-time variable data". FHS 3.0.
^ "File System Standard" (PDF). Linux Foundation. p. 5.11.1.
^ Red Hat reference guide on file system structure
^ SuSE Linux Enterprise Server Administration, Novell authorized courseware, by Jason W. Eckert, Novell; Course Technology, 2006;
ISBN 1-4188-3731-8,
ISBN 978-1-4188-3731-0
^ Debian policy on FHS compliance
^ Ubuntu Linux File system Tree Overview - Community Ubuntu Documentation
^ Hisham Muhammad (9 May 2003). "The Unix tree rethought: an introduction to GoboLinux". Retrieved 2016-10-04.
^ Dolstra, E. and Löh, A. "NixOS: A Purely Functional Linux Distribution." In ICFP 2008: 13th ACM SIGPLAN International Conference on Functional Programming, pages 367–378, Victoria, British Columbia, Canada. September 2008.
^ "5.3 About the /sys Virtual File System". docs.oracle.com. Oracle. Archived from the original on 8 July 2016. Retrieved 8 July 2016.
^ Lehey, Greg (May 2003). The Complete FreeBSD: Documentation from the Source (Fourth ed.). O'Reilly Media, Incorporated. pp. 188, 609. ISBN 9780596005160. Retrieved 8 July 2016.
^ Allan McRae. "Arch Linux - News: The /lib directory becomes a symlink". archlinux.org. Archived from the original on 9 September 2014. Retrieved 28 December 2014.
^ Allan McRae. "Arch Linux - News: Binaries move to /usr/bin requiring update intervention". archlinux.org. Archived from the original on 10 September 2014. Retrieved 28 December 2014.
^ https://lwn.net/Articles/436012/
^ http://wiki.debian.org/ReleaseGoals/RunDirectory
^ "FSSTND FAQ page". Retrieved 2016-05-10.
^ – FreeBSD Miscellaneous Information Manual
^ SunOS 4.1.3 manual page for filesystem(7), dated 10 January 1988 (from the FreeBSD Man Pages library)
^ – Solaris 10 Standards, Environments and Macros Reference Manual
^ "filesystem man page - Solaris 10 11/06 Man Pages". Retrieved 2011-10-15.
^ "Index of /pub/Linux/docs/fsstnd/old/fsstnd-1.0/". Ibiblio.org. Retrieved 2012-10-16.
^ "Index of /pub/Linux/docs/fsstnd/old/fsstnd-1.1/". Ibiblio.org. Retrieved 2012-10-16.
^ "Index of /pub/Linux/docs/fsstnd/old/". Ibiblio.org. Retrieved 2012-10-16.
^ "FHS 2.0 Announcement". Pathname.com. Retrieved 2012-10-16.
^ Quinlan, Daniel (14 March 2012) [1997], "FHS 2.0 Announcement", BSD, Linux, Unix and The Internet - Research by Kenneth R. Saborio, San Jose, Costa Rica: Kenneth R. Saborio, retrieved 18 February 2016
^ "Index of /pub/Linux/docs/fsstnd/". Ibiblio.org. Retrieved 2012-10-16.
^ "FHS 2.1 Announcement". Pathname.com. Retrieved 2012-10-16.
^ "FHS 2.1 is released". Lists.debian.org. 2000-04-13. Retrieved 2012-10-16.
^ Quinlan, Daniel (12 April 2000). "Filesystem Hierarchy Standard — Version 2.1, Filesystem Hierarchy Standard Group" (PDF). Acadia Linux Tutorials. Wolfville, Nova Scotia, Canada: Jodrey School of Computer Science, Acadia University. Retrieved 18 October 2012.
^ Russell, Rusty; Quinlan, Daniel, eds. (23 May 2001). "Filesystem Hierarchy Standard — Version 2.2 final Filesystem Hierarchy Standard Group" (PDF). Filesystem Hierarchy Standard. Retrieved 18 February 2016.
^ Russell, Rusty; Quinlan, Daniel; Yeoh, Christopher, eds. (28 January 2004). "Filesystem Hierarchy Standard - Filesystem Hierarchy Standard Group" (PDF). Retrieved 2014-11-29.
^ Yeoh, Christopher; Russell, Rusty; Quinlan, Daniel, eds. (19 March 2015). "Filesystem Hierarchy Standard" (PDF). The Linux Foundation. Retrieved 2015-05-20.
External links
Official Home of the Filesystem Hierarchy Standard (FHS) at The Linux Foundation
- Full specification texts
objectroot – a proposal for a new filesystem hierarchy, based on object-oriented design principles- The Dotted Standard Filename Hierarchy, yet another very different hierarchy (used in cLIeNUX) (mirror)
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