Filesystem Hierarchy Standard

Filesystem Hierarchy Standard
Filesystem Hierarchy Standard
Developed by Linux Foundation
Initial release February 14, 1994; 17 years ago (1994-02-14)
Latest release 2.3 / January 29, 2004; 7 years ago (2004-01-29)
Website (Historical)

The Filesystem Hierarchy Standard (FHS) defines the main directories and their contents in Linux operating systems. For the most part, it is a formalization and extension of the traditional BSD filesystem hierarchy.

The FHS is maintained by the Linux Foundation, a non-profit organization consisting of major software and hardware vendors, such as HP, Red Hat, IBM and Dell.

The current version is 2.3, announced on January 29, 2004.[1]



Most Linux distributions follow the FHS and declare it their own policy to maintain FHS compliance.[2][3][4][5]

When the FHS was created, other UNIX and Unix-like operating systems already had their own standards, notably the hier(7) description of file system layout[6] that has existed since the release of Version 7 Unix (in 1979), or the SunOS filesystem(7),[7] later Solaris filesystem(5).[8] [9]

Modern Linux distributions include a /sys directory as a virtual filesystem (sysfs, comparable to /proc, which is a procfs), which stores and allows modification of the devices connected to the system, whereas many traditional UNIX and Unix-like operating systems use /sys as a symbolic link to the kernel source tree.[citation needed]

Some Linux systems such as GoboLinux and Syllable Server use a completely different approach from the FHS.[clarification needed]


The process of developing a standard filesystem hierarchy began in August 1993 with an effort to restructure the file and directory structure of Linux. The FSSTND (Filesystem Standard), a filesystem hierarchy standard specific to the Linux operating system, was released on 14 February 1994. Subsequent revisions were released on 9 October 1994 and 28 March 1995.[10]

In early 1996, the goal of developing a more comprehensive version of FSSTND to address not only Linux, but other Unix-like systems was adopted with the help of members of the BSD development community. As a result, a concerted effort was made to focus on issues that were general to Unix-like systems. In recognition of this widening of scope, the name of the standard was changed to Filesystem Hierarchy Standard.

Release history

Red Old Standard/Draft; not supported
Yellow Old Standard; still supported
Green Current Standard
Blue Future Draft
Version Release Date Notes
v1.0 1994-02-14 FSSTND[11]
v1.1 1994-10-09 FSSTND[12]
v1.2 1995-03-28 FSSTND[13]
v2.0 1997-10-26 FHS 2.0 is the direct successor for FSSTND 1.2. Name of the standard was changed to Filesystem Hierarchy Standard.[14][15][16]
v2.1 2000-04-12 FHS[17][18][19]
v2.2 2001-05-23 FHS[20]
v2.3 2004-01-29 FHS[21]
v3.0 TBA FHS[22]

Directory structure

In the FHS all files and directories appear under the root directory "/", even if they are stored on different physical devices. Note however that some of these directories may or may not be present on a Unix system depending on whether certain subsystems, such as the X Window System, are installed.

The majority of these directories exist in all UNIX 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.
/bin/ Essential command binaries that need to be available in single user mode; for all users, e.g., cat, ls, cp.
/boot/ Boot loader files, e.g., kernels, initrd; often a separate partition[23]
/dev/ Essential devices, e.g., /dev/null.
/etc/ 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, /etc is referred to as the etcetera directory,[24] as this directory historically held everything that did not belong elsewhere (however, the FHS restricts /etc to static configuration files and may not contain binaries).[25] Since the publication of early documentation, the directory name has been re-designated in various ways. Recent interpretations include Backronyms such as "Editable Text Configuration" or "Extended Tool Chest".[26]

Configuration files for /opt/.
Configuration files for the X Window System, version 11.
Configuration files for SGML.
Configuration files for XML.
/home/ Users' home directories, containing saved files, personal settings, etc.; often a separate partition.
/lib/ Libraries essential for the binaries in /bin/ and /sbin/.
/media/ Mount points for removable media such as CD-ROMs (appeared in FHS-2.3).
/mnt/ Temporarily mounted filesystems.
/opt/ Optional application software packages.[27]
/proc/ Virtual filesystem documenting kernel and process status as text files, e.g., uptime, network. In Linux, corresponds to a Procfs mount.
/root/ Home directory for the root user.
/sbin/ Essential system binaries, e.g., init, ip, mount.
/srv/ Site-specific data which is served by the system.
/tmp/ Temporary files (see also /var/tmp). Often not preserved between system reboots.
/usr/ Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.[28]
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/.
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.
Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, e.g., bin/, lib/, share/.[29]
/var/ 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. Sometimes a separate partition.
Application cache data. Such data is locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. The cached files can be deleted without data loss
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.
Users' mailboxes.
Information about the running system since last boot, e.g., currently logged-in users and running daemons.
Spool for tasks waiting to be processed, e.g., print queues and unread mail.
Deprecated location for users' mailboxes.
Temporary files to be preserved between reboots.

Notes and references

  1. ^ (ANNOUNCE) FHS 2.3 Released, From: Christopher Yeoh - 2004-01-29, Email Archive: freestandards-fhs-discuss (read-only), Free Standards Group,
  2. ^ Red Hat reference guide on file system structure
  3. ^ SuSE Linux Enterprise Server Administration, Novell authorized courseware, by Jason W. Eckert, Novell; Course Technology, 2006; ISBN 1418837318, 9781418837310
  4. ^ Debian policy on FHS compliance
  5. ^ Ubuntu Linux File system Tree Overview - Community Ubuntu Documentation
  6. ^ hier(7) – FreeBSD Miscellaneous Information Manual
  7. ^ SunOS 4.1.3 manual page for filesystem(7), dated 10 January 1988 (from the FreeBSD Man Pages library)
  8. ^ filesystem(5) – Solaris 10 Standards, Environments and Macros Reference Manual
  9. ^ "filesystem man page - Solaris 10 11/06 Man Pages". Retrieved 2011-10-15. 
  10. ^ The Linux Filesystem Standard, by Garrett D'Amore, Page 45-47 in Linux Journal, July 1995, Issue 15
  11. ^
  12. ^
  13. ^
  14. ^
  15. ^
  16. ^
  17. ^
  18. ^
  19. ^
  20. ^
  21. ^
  22. ^
  23. ^ A separate partition is generally only used when bootloaders are incapable of reading the main filesystem (e.g. SILO does not recognize XFS) or other problems not easily resolvable by users.
  24. ^ J. DeFelicc (1972-03-17). "E.0". Preliminary Release of UNIX Implementation Document. p. 8. IMO.1-1. 
  25. ^
  26. ^ Define - /etc?, Posted by Cliff, March 03 2007 - Slashdot
  27. ^
  28. ^ Should be shareable and read-only, cf.
  29. ^ Historically and strictly according to the standard, /usr/local/ is 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/local/ is used for installing software/data that are not part of the standard operating system distribution (in such case, /usr/ would 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).

External links

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