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
windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
,
network connections,
processes
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that produce a specific se ...
, 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. 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, is included in the Plan 9 distribution. A 9P
OS X client
kernel extension is provided by Mac9P. A kernel client driver implementing 9P with some extensions for
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which i ...
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.
Server applications
Many of Plan 9's applications take the form of 9P file servers. Examples include:
*
acme: a text editor/development environment
*
rio: the Plan 9 windowing system
*
plumber: interprocess communication
* ftpfs: an
FTP client that presents the files and directories on a remote FTP server in the local
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
A Uniform Resource Locator (URL), colloquially termed as a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifie ...
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 filesystem is required:
*
NixOS: a purely functional and declarative Linux distribution can rebuild itself inside a
virtual machine
In computing, a virtual machine (VM) is the virtualization/ emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized har ...
, where the client uses 9P to mount the package store directory of the host.
*
Windows Subsystem for Linux: since Windows 10 version 1903, the subsystem implements 9P as a server and the host Windows operating system acts as a client.
*
Crostini
Crostini (meaning "little crusts" in Italian; singular ''crostino'') are an Italian appetizer consisting of small slices of grilled or toasted bread and toppings. The toppings may include a variety of different cheeses, meats, vegetables and ...
: a custom 9P server is used to provide access to files outside of a Linux VM
*
QEMU: the VirtFS device allows for filesystem sharing over 9P, which is accelerated with kernel drivers and shared memory
Distributed I/O Daemon - a 9P file server
See also
*
Distributed file system
*
*
References
External links
9P Resourcespage at cat-v.org
9P ManualThe Styx Architecture for Distributed Systems
by Rob Pike and Dennis Ritchie
The Organization of Networks in Plan 9
by Dave Presotto and Phil Winterbottom
Security in Plan 9
{{File systems
Application layer protocols
Inferno (operating system)
Inter-process communication
Internet Protocol based network software
Network file systems
Network file transfer protocols
Network protocols
Plan 9 from Bell Labs