View source for 9P (protocol)

{{Short description|A network protocol developed for the Plan 9 distributed operating system}}
{{Multiple issues|
{{Technical|date=February 2017}}
{{Primary sources|date=August 2015}}
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{{Infobox networking protocol
| title        = 9P
| logo         = 
| logo alt     = 
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| caption      = 
| is stack     = No
| abbreviation = 
| purpose      = Connecting components
| developer    = [[Bell Labs]]
| date         = {{Start date and age|1992}}
| based on     = 
| influenced   = 9P2000
| osilayer     = 
| ports        = 
| rfcs         = 
| hardware     = 
}}
{{IPstack}}
'''9P''' (or the '''Plan 9 Filesystem Protocol''' or '''Styx''') is a [[network protocol]] developed for the [[Plan 9 from Bell Labs]] [[distributed operating system]] as the means of connecting the components of a Plan 9 system. Files are key objects in Plan 9. They represent [[window (computing)|windows]], [[computer network|network]] connections, [[process (computing)|processes]], and almost anything else available in the operating system.

9P was revised for the 4th edition of Plan 9 under the name '''9P2000''', containing various improvements. Some of the improvements made are the removal of certain filename restrictions, the addition of a 'last modifier' metadata field for directories, and authentication files.<ref>{{Cite web|url=https://9p.io/plan9/about.html|title=Plan 9 from Bell Labs — Overview|website=9p.io}}</ref> The latest version of the [[Inferno operating system]] also uses 9P2000. The Inferno file protocol was originally called Styx, but technically it has always been a variant of 9P.

A server implementation of 9P for Unix, called u9fs,<ref>{{Cite web|url=https://www.netlib.org/research/|title=research: u9fs.tgz is the source code tarbal|website=www.netlib.org}}</ref><ref>{{Cite web|url=http://9p.io/magic/man2html/4/u9fs|title=Plan 9 /sys/man/4/u9fs|website=9p.io}}</ref> is included in the Plan 9 distribution. A 9P [[OS X]] client [[kernel extension]] is provided by Mac9P.<ref>{{Cite web|url=https://github.com/benavento/mac9p|title=9P for Mac|author=benavento|date=April 19, 2019|via=GitHub}}</ref> A kernel client driver implementing 9P with some extensions for [[Linux]] is part of the [[v9fs]] project. 9P and its derivatives have also found application in embedded environments, such as the Styx-on-a-Brick project for [[Lego_Mindstorms#RCX|Lego Mindstorms Bricks]].<ref>{{Cite web |url=http://doc.cat-v.org/inferno/4th_edition/styx-on-a-brick/ |title=Styx-on-a-Brick |website=Cat-V Doc }}</ref>

== Server applications ==
Many of Plan 9's applications take the form of 9P file servers. Examples include:
* [[acme (text editor)|acme]]: a text editor/development environment
* [[rio (windowing system)|rio]]: the Plan 9 windowing system
* [[plumber (Plan 9)|plumber]]: interprocess communication
* ftpfs: an [[File Transfer Protocol|FTP]] client that presents the files and directories on a remote FTP server in the local [[Plan 9 from Bell Labs#Union directories and namespaces|namespace]]
* wikifs: a [[wiki]] editing tool that presents a remote wiki as files in the local namespace
* webfs: a file server that retrieves data from [[URL]]s and presents the contents and details of responses as files in the local namespace

Outside of Plan 9, the 9P protocol is still used when a lightweight remote file system is required:
* [[NixOS]]: a Linux distribution that uses the [[Nix package manager]]. NixOS can rebuild itself inside a [[virtual machine]], where the client uses 9P to mount the package store directory of the host.
* [[GNU Guix]]: a [[package manager]] that can instantiate and manage [[Unix-like]] operating systems. It can instantiate a system inside a [[virtual machine]] in the same manner that [[NixOS]] does
* [[Windows Subsystem for Linux]] (WSL): since Windows 10 version 1903, the subsystem implements 9P as a server and the host Windows operating system acts as a client.<ref>{{Cite web|url=https://devblogs.microsoft.com/commandline/whats-new-for-wsl-in-windows-10-version-1903/|title=What's new for WSL in Windows 10 version 1903?|date=February 16, 2019|website=Windows Command Line Tools For Developers}}</ref>
* [[Chrome_OS#Linux_apps|Crostini]]: a custom 9P server is used to provide access to files outside of a Linux VM <ref>{{Cite web|url=https://chromium.googlesource.com/chromiumos/docs/+/master/containers_and_vms.md#Overview|work=Chromium OS Docs|title=Running Custom Containers Under Chrome OS|access-date=2019-03-28}}</ref>
* [[QEMU]]: the VirtFS device allows for filesystem sharing over 9P, which is accelerated with kernel drivers and shared memory <ref>{{Cite journal|last1=Jujjuri|first1=Venkateswararao|last2=Van Hensbergen|first2=Eric|last3=Liguori|first3=Anthony|last4=Pulavarty|first4=Badari|date=July 13–16, 2010|title=VirtFS—A virtualization aware File System pass-through|url=https://www.kernel.org/doc/ols/2010/ols2010-pages-109-120.pdf|journal=Linux Symposium}}</ref><ref>{{Cite web|url=https://wiki.qemu.org/Documentation/9psetup|title=Documentation/9psetup|website=QEMU Docs|access-date=2019-03-28}}</ref>
* [https://github.com/chaos/diod DIOD]: Distributed I/O Daemon{{dash}}a 9P file server

== See also ==
* [[Distributed file system]]
* {{Annotated link|Everything is a file}}
* {{Annotated link|IL (network protocol)|IL}}

== References ==
{{Reflist|30em}}

== External links ==
* [http://9p.cat-v.org/ 9P Resources] page at cat-v.org
* [http://man.cat-v.org/plan_9/5/intro 9P Manual]
* [http://doc.cat-v.org/inferno/4th_edition/styx The Styx Architecture for Distributed Systems] by [[Rob Pike]] and [[Dennis Ritchie]]
* [http://doc.cat-v.org/plan_9/4th_edition/papers/net/ The Organization of Networks in Plan 9] by Dave Presotto and Phil Winterbottom
* [http://doc.cat-v.org/plan_9/4th_edition/papers/auth Security in Plan 9]

{{File systems}}

[[Category:Computer-related introductions in 1992]]
[[Category:Application layer protocols]]
[[Category:Inferno (operating system)]]
[[Category:Inter-process communication]]
[[Category:Internet Protocol based network software]]
[[Category:Network file systems]]
[[Category:Network file transfer protocols]]
[[Category:Plan 9 from Bell Labs]]