View source for Aufs

{{Short description|Linux filesystem}}
{{lowercase}}
{{distinguish|AUFS}}
{{Infobox filesystem
| name                    = aufs
| full_name               = Advanced multi layered unification filesystem
| developer               = [[Junjiro Okajima]]
| introduction_os         = 
| introduction_date       = 2006
| partition_id            = 
| directory_struct        = 
| file_struct             = 
| bad_blocks_struct       = 
| max_filename_size       = 
| max_files_no            = 
| max_volume_size         = 
| max_file_size           = 
| filename_character_set  = 
| dates_recorded          = 
| date_range              = 
| date_resolution         = 
| forks_streams           = 
| attributes              = 
| file_system_permissions = [[POSIX]]
| compression             = 
| encryption              = 
| OS                      = [[Linux]] via third-party [[Loadable kernel module|kernel module]]
| website                 = [https://aufs.sourceforge.net/ aufs.sourceforge.net]
}}

'''aufs''' (short for '''advanced multi-layered unification filesystem''') implements a [[union mount]] for [[Linux]] [[file system]]s. The name originally stood for '''AnotherUnionFS''' until version 2.

Developed by [[Junjiro Okajima]] in 2006,<ref>{{cite web|title=History of aufs|url=http://aufs.sourceforge.net/History|access-date=2015-11-08}}</ref> aufs is a complete rewrite of the earlier [[UnionFS]]. It aimed to improve reliability and performance, but also introduced some new concepts, like writable branch balancing,<ref>[http://aufs.sourceforge.net/ Goals and new features of aufs in the project's homepage]</ref> and other improvements – some of which are now implemented in the UnionFS 2.x branch.

aufs was rejected for merging into mainline Linux. Its code was criticized for being "dense, unreadable, [and] uncommented".<ref>{{cite web|last1=Aurora|first1=Valerie|title=Unioning file systems: Implementations, part 2|url=https://lwn.net/Articles/327738/|website=[[LWN.net]]|access-date=2015-11-08|date=2009-04-07}}</ref> Instead, [[OverlayFS]] was merged in the Linux kernel.<ref>{{cite web|url=https://github.com/torvalds/linux/commit/e9be9d5e76e34872f0c37d72e25bc27fe9e2c54c|title=overlay filesystem · torvalds/linux@e9be9d5|website=[[GitHub]] |access-date=12 July 2016}}</ref><ref>{{cite web|last1=Hellwig|first1=Christoph|title=Re: [RFC Aufs2 #5 28/29] export lookup functions|url=http://marc.info/?l=linux-kernel&m=123938533724484&w=2|access-date=2015-11-08|date=2009-04-10}}</ref> After several attempts to merge aufs into mainline kernel, the author has given up.<ref>{{cite web|last1=Okajima|first1=Junjiro|title=Re: [RFC Aufs2 #5 28/29] export lookup functions|url=https://marc.info/?l=linux-kernel&m=123938442923108|access-date=2018-10-01|date=2009-04-10}}</ref>

==Use==
Aufs is included in [[Debian]] "Jessie" (v8) and [[Ubuntu (operating system)|Ubuntu]] 16.04 out of the box. Debian "Stretch" (v9) does not include aufs anymore, but provides a package aufs-dkms, which auto-compiles the aufs kernel module using [[Dell]]'s [[Dynamic Kernel Module Support|dkms]].

[[Docker (software)|Docker]] originally used aufs for container filesystem layers. It is still available as one of the storage backends but is deprecated in favour of the {{mono|overlay2}} backend which uses [[OverlayFS]].<ref>{{cite web|title=Deprecated Engine Features|website=[[GitHub]] |url=https://github.com/docker/cli/blob/master/docs/deprecated.md|access-date=2020-10-26}}</ref>

Several [[Linux distribution]]s have chosen aufs as a replacement for UnionFS, including:
* [[Knoppix]] [[live CD]] [[Linux distribution]] – since the end of 2006, "for better stability and performance"<ref>{{cite web|title=KNOPPIX 5.1 - Live Linux Filesystem On CD|url=http://www.knopper.net/knoppix/knoppix51-en.html|publisher=knopper.net|access-date=2015-11-08|date=2013-01-05}}</ref>
* [[NimbleX]] since version 2008. Switched simultaneously with Linux-Live
* [[Porteus (operating system)|Porteus]] LiveCD, run fully in RAM
* [[Slax]] (and Linux-Live scripts in general) since version 6<ref>[http://www.linux-live.org/?changes Linux Live scripts] {{Webarchive|url=https://web.archive.org/web/20090322090540/http://www.linux-live.org/?changes |date=2009-03-22 }}  use AUFS for better stability</ref>
* [[Xandros]] Linux distribution, available in the ASUS [[Eee PC]] model 901
* [[Ubuntu (operating system)|Ubuntu]] 10.04 LTS Live CD
* [[Debian]] 6.0 Live media
* [[Gentoo Linux]] LiveDVD 11.0<ref>{{cite web|url=http://www.gentoo.org/news/20110308-livedvd.xml |title=Gentoo Linux - Gentoo Linux - LiveDVD 11.0 |publisher=Gentoo.org |date=2011-03-08 |access-date=2012-04-19 |url-status=dead |archive-url=https://web.archive.org/web/20120413110015/http://www.gentoo.org/news/20110308-livedvd.xml |archive-date=2012-04-13 }}</ref>
* [[Gentoo Linux]] LiveDVD 11.2<ref>{{cite web|url=http://www.gentoo.org/news/20110807-livedvd.xml |title=Gentoo Linux - Gentoo Linux releases 11.2 LiveDVD |publisher=Gentoo.org |date=2011-08-07 |access-date=2012-04-19 |url-status=dead |archive-url=https://web.archive.org/web/20120417064501/http://www.gentoo.org/news/20110807-livedvd.xml |archive-date=2012-04-17 }}</ref>
* [[Gentoo Linux]] LiveDVD 12.0<ref>{{cite web|url=http://www.gentoo.org/news/20120102-livedvd.xml |title=Gentoo Linux - Gentoo Linux releases 12.0 LiveDVD |publisher=Gentoo.org |date=2012-01-02 |access-date=2012-04-19 |url-status=dead |archive-url=https://web.archive.org/web/20120421204113/http://www.gentoo.org/news/20120102-livedvd.xml |archive-date=2012-04-21 }}</ref>
* [[Salix OS#LiveCD version|Salix Live]] via Linux-Live scripts until version 13.1.1 and via SaLT from version 13.37
* [[Puppy linux|Puppy Linux]] versions can run fully in RAM with changes saved to disk on shutdown. For example, Slacko 5.3.3 running as a LiveCD.
* [[Manjaro Linux]] via their patched official kernels <ref>{{cite web|url=https://gitlab.manjaro.org/packages/core/linux54/blob/master/PKGBUILD |title=Manjaro linux54 kernel PKGBUILD|date=2020-01-19 |access-date=2020-01-19}}</ref>

==See also==
{{Portal|Free and open-source software}}
* [[OverlayFS]], the competing project that was chosen for merger to the Linux core
* [[File system]]
* [[Union mount]], describing the concept of merging file system branches
* [[UnionFS]], an older union mount project
* [[Syslinux]]

==References==
{{Reflist}}

==External links==
* [http://aufs.sourceforge.net/ AuFS project homepage]
* [http://bbs.archlinux.org/viewtopic.php?pid=314698 A simple example]

{{File systems}}

[[Category:Free special-purpose file systems]]
[[Category:File systems supported by the Linux kernel]]
[[Category:Union file systems]]