Filesystem Hierarchy Standard

The Filesystem Hierarchy Standard (FHS) defines the main directories and their contents in most software systems using Linux operating system. It is a formalization and extension of common UNIX practices.

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

Overview

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 February 14, 1994. Subsequent revisions were released on October 9, 1994 and March 28, 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, or FHS for short.

The FHS is maintained by the Free Standards Group, a non-profit organization consisting of major software and hardware vendors, such as HP, Red Hat, IBM and Dell. Still, the vast majority of the Linux distributions, including those developed by members of the Free Standards Group, do not follow this proposed standard 100%. In particular, paths specifically created by the FHS editors, such as /srv/, do not see widespread usage.

Some Linux systems reject the FHS in favor of a different approach, as in GoboLinux. Since the FHS began as a Linux initiative, other UNIX and Unix-like operating systems generally completely ignore it in favor of their own systems, which sometimes vary wildly — for example, Mac OS X uses more readable names such as /Library/, /Applications/, and /Users/ in tandem with its traditional UNIX directory hierarchy.

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.
/dev/	Essential devices (e.g., /dev/null).
/etc/	Host-specific system-wide configuration files (the name comes from et cetera).
/etc/opt/	Configuration files for /opt/.
/etc/X11/	Configuration files for the X Window System, version 11.
/etc/sgml/	Configuration files for SGML.
/etc/xml/	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.
/proc/	Virtual filesystem documenting kernel and process status as text files (e.g., uptime, network).
/root/	Home directory for the root user.
/sbin/	Essential system binaries (e.g., init, route, ifup).
/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 user data; contains the majority of (multi-)user utilities and applications.
/usr/bin/	Non-essential command binaries (not needed in single user mode); for all users.
/usr/include/	Standard include files.
/usr/lib/	Libraries for the binaries in /usr/bin/ and /usr/sbin/.
/usr/sbin/	Non-essential system binaries (e.g. daemons for various network-services).
/usr/share/	Architecture-independent (shared) data.
/usr/src/	Source code (e.g. the kernel source code with its header files).
/usr/X11R6/	X Window System, Version 11, Release 6.
/usr/local/	Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, eg. bin/, lib/, share/.
/var/	Variable files, such as logs, spool files, and temporary e-mail files.
/var/lib/	State information. Persistent data modified by programs as they run (e.g. databases, packaging system metadata etc.).
/var/lock/	Lock files. Files keeping track of resources currently in use.
/var/log/	Log files. Various logs.
/var/mail/	Users' mailboxes.
/var/run/	Information about the running system since last boot (e.g. currently logged-in users and running daemons).
/var/spool/	Spool for tasks waiting to be processed (e.g. print queues and unread mail).
/var/spool/mail/	Deprecated location for users' mailboxes.
/var/tmp/	Temporary files to be preserved between reboots.

See also

• Linux Standard Base
• GoboLinux

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 (January 29, 2004)