9P
lastmod 2025-11-13created 2025-11-131 edits
9P (the Plan 9 Filesystem Protocol, or Styx) is a network protocol developed for the Plan 9 operating system that connects the components of a Plan 9 system. Files are key objects in Plan 9. They represent windows, network connections, processes, and everything else available in the operating system. Unlike NFS, 9P strengthens cache handling and also provides synthetic files (for example, /proc to represent processes).
9P was revised for the 4th edition of Plan 9 under the name 9P2000, which contained various important improvements. 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 treated as a variant of 9P.
Another variant, 9p2000.u, is a revision with better support for Unix environments; for details, see v9fs 9p2000.u. A server implementation of 9P for Unix, called u9fs, is included in the Plan 9 distribution. A kernel client driver 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.