Editing Filesystem Hierarchy Standard (section)

== FHS compliance ==
Most [[Linux distribution]]s follow the Filesystem Hierarchy Standard and declare it their own policy to maintain FHS compliance.<ref>[[Red Hat]] reference guide on [https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html-single/Storage_Administration_Guide/index.html#s1-filesystem-fhs file system structure].</ref><ref>[[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}}.</ref><ref>[[Debian]] policy on [https://www.debian.org/doc/debian-policy/#file-system-hierarchy FHS compliance].</ref><ref>[[Ubuntu]] [https://help.ubuntu.com/community/LinuxFilesystemTreeOverview Linux File system Tree Overview]{{snd}} Community Ubuntu Documentation.</ref> [[GoboLinux]]<ref>{{cite web | title = The Unix tree rethought: an introduction to GoboLinux | url = http://www.gobolinux.org/?page=k5 | author = Hisham Muhammad | date = 9 May 2003 | access-date = 2016-10-04}}</ref> and [[NixOS]]<ref>{{cite conference |last1=Dolstra |first1=E. |last2=Löh |first2=A. |url=https://nixos.org/~eelco/pubs/nixos-icfp2008-final.pdf |title=NixOS: A Purely Functional Linux Distribution |conference-url=http://www.icfpconference.org/icfp2008/ |conference=ICFP 2008: 13th ACM SIGPLAN International Conference on Functional Programming |pages=367–378 |location=Victoria, British Columbia, Canada |date=September 2008}}</ref> provide examples of intentionally non-compliant filesystem implementations.

Some distributions generally follow the standard but deviate from it in some areas. The FHS is a "trailing standard", and so documents common practices at a point in time. Of course, times change, and distribution goals and needs call for experimentation. Some common deviations include:
* Modern Linux distributions include a <code>/sys</code> directory as a [[virtual filesystem]] ([[sysfs]], comparable to <code>/proc</code>, which is a [[procfs]]), which stores and allows modification of the devices connected to the system,<ref>{{cite web |title=5.3 About the /sys Virtual File System |url=http://docs.oracle.com/cd/E37670_01/E41138/html/ol_sysfs.html |website=docs.oracle.com |publisher=Oracle |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20160708193213/https://docs.oracle.com/cd/E37670_01/E41138/html/ol_sysfs.html |archive-date=8 July 2016}}</ref> whereas many traditional [[Unix-like]] operating systems use <code>/sys</code> as a [[symbolic link]] to the [[Kernel (operating system)|kernel]] source tree.<ref>{{cite book |last1=Lehey |first1=Greg |title=The Complete FreeBSD: Documentation from the Source |date=May 2003 |publisher=O'Reilly Media, Incorporated |isbn=9780596005160 |pages=188, 609 |edition=Fourth |url=https://books.google.com/books?id=7Y5kfaRmtKUC}}</ref>
* Many modern Unix-like systems (such as [[FreeBSD]] and [[OpenBSD]]) via their [[Ports collection|ports systems]] install third-party packages into <code>/usr/local</code>, while keeping code considered part of the operating system in <code>/usr</code>.
* Some Linux distributions no longer differentiate between <code>/lib</code> and <code>/usr/lib</code> and have <code>/lib</code> symlinked to <code>/usr/lib</code>.<ref>{{cite web |author1=Allan McRae |title=Arch Linux – News: The /lib directory becomes a symlink |url=https://www.archlinux.org/news/the-lib-directory-becomes-a-symlink/ |website=archlinux.org |access-date=14 December 2019 |archive-url=https://web.archive.org/web/20140909234433/https://www.archlinux.org/news/the-lib-directory-becomes-a-symlink/ |archive-date=9 September 2014 |url-status=live}}</ref>
* Some Linux distributions no longer differentiate between <code>/bin</code> and <code>/usr/bin</code> and between <code>/sbin</code> and <code>/usr/sbin</code>. They may symlink <code>/bin</code> to <code>/usr/bin</code> and <code>/sbin</code> to <code>/usr/sbin</code>. Other distributions choose to consolidate all four, symlinking them to <code>/usr/bin</code>.<ref>{{cite web |author1=Allan McRae |title=Arch Linux – News: Binaries move to /usr/bin requiring update intervention |url=https://www.archlinux.org/news/binaries-move-to-usrbin-requiring-update-intervention/ |website=archlinux.org |access-date=15 December 2019 |archive-url=https://web.archive.org/web/20140910093202/https://www.archlinux.org/news/binaries-move-to-usrbin-requiring-update-intervention/ |archive-date=10 September 2014 |url-status=live}}</ref>

Modern Linux distributions include a <code>/run</code> 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 <code>/var/run</code>, 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 <code>/dev/.udev</code>, <code>/dev/.mdadm</code>, <code>/dev/.systemd</code> or <code>/dev/.mount</code> directories, even though the device directory is not intended for such data.<ref>{{cite mailing list |url=https://www.mail-archive.com/devel@lists.fedoraproject.org/msg23576.html |title=What's this /run directory doing on my system and where does it come from? |author=Lennart Poettering |date=30 March 2011 |mailing-list=devel@lists.fedoraproject.org}}</ref> 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:<ref>{{cite web |url=http://wiki.debian.org/ReleaseGoals/RunDirectory |title=ReleaseGoalsRunDirectory |website=Debian Wiki}}</ref>
* <code>/dev/.*</code> → <code>/run/*</code>
* <code>/dev/shm</code> → <code>/run/shm</code>
* <code>/dev/shm/*</code> → <code>/run/*</code>
* <code>/etc/*</code> (writeable files) → <code>/run/* </code>
* <code>/lib/init/rw</code> → <code>/run</code>
* <code>/var/lock</code> → <code>/run/lock</code>
* <code>/var/run</code> → <code>/run</code>
* <code>/tmp</code> → <code>/run/tmp</code>