Plan 9 from Bell Labs is an operating system designed by the Computing Science Research Center (CSRC) at Bell Labs in the mid-1980s, built on the UNIX concepts first developed there in the late 1960s. Since 2000, Plan 9 has been free and open-source. The final official release was in early 2015.

Under Plan 9, UNIX's everything is a file metaphor is extended via a pervasive network-centric (distributed) filesystem, and the cursor-addressed, terminal-based I/O at the heart of UNIX is replaced by a windowing system and graphical user interface without cursor addressing (although rc, the Plan 9 shell, is text-based). Plan 9 also introduced capability-based security and a log-structured file system called Fossil that provides snapshotting and versioned file histories.

The name Plan 9 from Bell Labs is a reference to the Ed Wood 1957 cult science fiction Z-movie Plan 9 from Outer Space. It explored several changes to the original Unix model that facilitate the use and programming of the system, notably in distributed multi-user environments. After several years of development and internal use, Bell Labs shipped the operating system to universities in 1992. Three years later, Plan 9 was made available for commercial parties by AT&T via the book publisher Harcourt Brace. With source licenses costing $350, AT&T targeted the embedded systems market rather than the computer market at large. Ritchie commented that the developers did not expect to do "much displacement" given how established other operating systems had become.

By early 1996, the Plan 9 project had been "put on the back burner" by AT&T in favor of Inferno, intended to be a rival to Sun Microsystems' Java platform.

In the late 1990s, Bell Labs' new owner Lucent Technologies dropped commercial support for the project and in 2000, a third release was distributed under an open-source license. A fourth release under a new free software license occurred in 2002.

As Bell Labs has moved on to later projects in recent years, development of the official Plan 9 system had stopped. On March 23, 2021, development resumed following the transfer of copyright from Bell Labs to the Plan 9 Foundation. Geoff Collyer, a Plan 9 maintainer, published his Plan 9 work on his personal homepage, which include the 64-bit 9k kernel and a RISC-V port. Unofficial development for the system also continues on the 9front fork, where active contributors provide monthly builds and new functionality. So far, the 9front fork has provided the system Wi-Fi drivers, audio drivers, USB support and built-in game emulator, along with other features. Other recent Plan 9-inspired operating systems include Harvey OS and Jehanne OS.

{| class="wikitable"

|-

! Date

! Release

! Comment

|-

| 1992

| Plan 9 1st edition

| Released by Bell Labs to universities

|-

| 1995

| Plan 9 2nd edition

| Released by Bell Labs for non-commercial purposes

Unix compatibility

Though Plan 9 was supposed to be a further development of Unix concepts, compatibility with preexisting Unix software was never the goal for the project. Many command-line utilities of Plan 9 share the names of Unix counterparts, but work differently.

Derivatives and forks

  • Inferno is a descendant of Plan 9, and shares many design concepts and even source code in the kernel, particularly around devices and the Styx/9P2000 protocol. Inferno shares with Plan 9 the Unix heritage from Bell Labs and the Unix philosophy. Many of the command line tools in Inferno were Plan 9 tools that were translated to Limbo.
  • 9atom augments the Plan 9 distribution with the addition of a 386 PAE kernel, an amd64 cpu and terminal kernel, nupas, extra pc hardware support, IL and Ken's fs. Its home page hasn't been updated since 2013, and very little is known about its development or community.
  • 9front is a fork of Plan 9. It was started to remedy a perceived lack of devoted development resources inside Bell Labs, and has accumulated various fixes and improvements.
  • 9legacy is an alternative distribution. It includes a set of patches based on the current Plan 9 distribution.
  • Akaros is designed for many-core architectures and large-scale SMP systems.
  • Harvey OS (discontinued) is an effort to get the Plan 9 code working with gcc and clang.
  • JehanneOS is an experimental OS derived from Plan 9. Its userland and modules are mostly derived from 9front, its build system from Harvey OS, and its kernel is a fork of the 9k 64-bit Plan9 kernel.
  • NIX is a fork of Plan9 aimed at multicore systems and cloud computing.
  • node9 is a scripted derivative of Plan9/Inferno that replaces the Limbo programming language and DIS virtual machine with the Lua language and LuaJit virtual machine. It also replaces the Inferno per-platform hosted I/O with Node.js' libuv eventing and I/O for consistent, cross-platform hosting. It's a proof-of-concept that demonstrates that a distributed OS can be constructed from per-process namespaces and generic cloud elements to construct a single-system-image of arbitrary size.
  • Plan B designed to work in distributed environments where the set of available resources is different at different points in time. Originally based on the third edition Plan 9 kernel, Plan B was moved into user space to run on current Plan 9 systems.
  • R9 is a reimplementation of the Plan 9 kernel on Rust (although there is no port of the Rust programming language compiler to Plan 9).

License

Starting with the release of Fourth edition in April 2002, and all previous releases have been relicensed to the MIT License.

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  • 9p.io: Archived mirror of the original official Plan 9 Web site at plan9.bell-labs.com
  • 9fans: Semi-official mailing list for Plan 9 users and developers
  • Plan 9 Foundation