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 traditional BSD filesystem hierarchy.
The current version is 2.3, announced on 29 January 2004.
Contents |
Overview
The FHS is maintained by the Free Standards Group, now The Linux Foundation, a non-profit organization consisting of major software and hardware vendors, such as HP, Red Hat, IBM and Dell. However, the vast majority (as of 2009) of the Linux distributions, including those developed by members of the Free Standards Group, do not follow the proposed standard completely. In particular, paths specifically invented by the FHS editors, such as /srv, do not see widespread usage.
Some Linux systems, such as GoboLinux, use a different approach. Also, when it was created, other UNIX and Unix-like operating systems already had their own standards.[1][2] For example, Mac OS X uses longer names such as /Library, /Applications, and /Users in tandem with its traditional UNIX directory hierarchy.
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. Likewise, Plan 9 from Bell Labs includes a /net directory.
History
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.
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.
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[3] |
| /dev/ | Essential devices, e.g., /dev/null. |
| /etc/ | Host-specific system-wide configuration files (the name comes from et cetera[4]). |
|
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[5]. |
| /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, route, 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.[6] |
|
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/.[7] |
| /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. |
|
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. |
See also
- Linux Standard Base
- GoboLinux
- Unix directory structure
- List of computer standards
- Special Folders: corresponding standard for MS Windows
Notes and references
- ^ "hier(7) manual page". http://man.freebsd.org/hier. Retrieved 2009-10-27.
- ^ http://www.freebsd.org/cgi/man.cgi?query=filesystem&apropos=0&sektion=0&manpath=SunOS+5.10&format=html
- ^ (footnote) 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.
- ^ J. DeFelicc (1972-03-17). "E.0". Preliminary Release of UNIX Implementation Document. p. 8. IMO.1-1. http://www.bitsavers.org/pdf/bellLabs/unix/PreliminaryUnixImplementationDocument_Jun72.pdf.
- ^ http://www.pathname.com/fhs/pub/fhs-2.3.html#OPTADDONAPPLICATIONSOFTWAREPACKAGES
- ^ 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/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
- Home of the Filesystem Hierarchy Standard
- Fortune Cookies through the /proc Filesystem
- The Dotted Standard Filename Hierarchy, yet another very different hierarchy (used in cLIeNUX)
- Filesystem Hierarchy Standard 2.3 (29 January 2004)
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