Filesystem Hierarchy Standard （Linux文件系统层次标准）

中文译文：文件系统层次结构标准(FHS)(for Linux)
本片文章的内容完全从wiki上复制过来,仅排版有所不同 , 完整内容请转至
wiki:https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

由[email protected]整理，
本文更新地址：http://blog.csdn.net/qq_29753285/article/details/69790931

Filesystem Hierarchy Standard (FHS)由linux基金会维护，
目前(2017-4-9)，FHS的最新版本为3.0，可从http://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.pdf下载

Filesystem Hierarchy Standard

Developed by Linux Foundation
Initial release 14 February 1994
Latest release 3.0 (3 June 2015)
Website Official website

The Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Unix-like operating systems. It is maintained by the Linux Foundation. The latest version is 3.0, released on 3 June 2015. Currently it is only used by Linux distributions.

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 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.

• / 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.
  • /dev Essential device files, 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, 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). Since the publication of early documentation, the directory name has been re-explained in various ways. Recent interpretations include backronyms such as "Editable Text Configuration" or "Extended Tool Chest".[5]
    
    • /etc/opt Configuration files for add-on packages that are stored in /opt/.
    • /etc/sgml Configuration files, such as catalogs, for software that processes SGML.
    • /etc/X11 Configuration files for the X Window System, version 11.
    • /etc/xml Configuration files, such as catalogs, for software that processes XML.
  • /home Users home directories, containing saved files, personal settings, etc.
  • /lib Libraries essential for the binaries in /bin/ and /sbin/.
  • /lib Alternate format essential libraries. Such directories are optional, but if they exist, they have some requirements.
  • /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 providing process and kernel information as files. In Linux, corresponds to a procfs mount.
  • /root Home directory for the root user.
  • /run Run-time variable data: Information about the running system since last boot, e.g., currently logged-in users and running daemons.
  • /sbin Essential system binaries, e.g., fsck, init, route.
  • /srv 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.
  • /sys Contains information about the devices connected to the computer.
  • /tmp Temporary files (see also /var/tmp). Often not preserved between system reboots, and may be severely size restricted.
  • /usr Secondary hierarchy for read-only 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/lib Alternate format libraries (optional).
    • /usr/local Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, e.g., bin/, lib/, share/.
    • /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 (up to FHS-2.3, optional).
  • /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.
    
    • /var/cache 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.
    • /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 Mailbox files. In some distributions, these files may be located in the deprecated /var/spool/mail.
    • /var/opt Variable data from add-on packages that are stored in /opt/.
    • /var/run Run-time variable data. This directory contains system information data describing the system since it was booted.
In FHS 3.0, /var/run is replaced by /run; a system should either continue to provide a /var/run directory, or provide a symbolic link from /var/run to /run, for backwards compatibility.[10]
    • /var/spool Spool for tasks waiting to be processed, e.g., print queues and outgoing mail queue.
      
      • /var/spool/mail Deprecated location for users mailboxes.
    • /var/tmp 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.GoboLinux and NixOS provide examples of intentionally non-compliant filesystem implementations.

Some distributions that generally follow the standard deviate from it in some areas. Common deviations include:

• 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,[18] whereas many traditional UNIX and Unix-like operating systems use /sys as a symbolic link to the kernel source tree.
• Many modern UNIX systems (like FreeBSD via its ports system) install third party packages into /usr/local while keeping code considered part of the operating system in /usr.
• Some Linux distributions no longer differentiate between /lib versus /usr/lib and have /lib symlinked to /usr/lib.
• Some Linux distributions no longer differentiate between /bin versus /usr/bin and /sbin versus /usr/sbin. They symlink /bin to /usr/bin and /sbin to /usr/sbin. And /usr/sbin may get symlinked to /usr/bin.

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. 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:

• /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

When the FHS was created as the FSSTND (short for “Filesystem Standard”), other UNIX and Unix-like operating systems already had their own standards. Notable examples are these: the hier(7) description of file system layout, which has existed since the release of Version 7 Unix (in 1979); the SunOS filesystem(7) and its successor, the Solaris filesystem(5).

Release history

legend	Version	Release Date	Notes
older version	1	1994/2/14	FSSTND
older version	1.1	1994/10/9	FSSTND
older version	1.2	1995/3/28	FSSTND
older version	2	1997/10/26	FHS 2.0 is the direct successor for FSSTND 1.2. Name of the standard was changed to Filesystem Hierarchy Standard.
older version	2.1	2000/4/12	FHS
older version	2.2	2001/5/23	FHS
still supported	2.3	2004/1/29	FHS
latest version	3	2015/5/18	FHS

See also

Unix directory structure
Intel Binary Compatibility Standard (iBCS)
hier(7)– Linux Programmer’s Manual – Overview, Conventions and Miscellanea