World Library  
Flag as Inappropriate
Email this Article

Plan 9 from Bell Labs

Plan 9 from Bell Labs
Glenda, the Plan 9 Bunny
Installation of Plan 9
Developer Bell Labs
Written in Dialect of ANSI C
Working state Current
Source model Open source
Initial release 1992 (universities) / 1995 (general public)
Latest release Fourth Edition / daily
Available in English
Update method replica
Platforms x86 / Vx32, x86-64, MIPS, DEC Alpha, SPARC, PowerPC, ARM
Kernel type Hybrid kernel
Default user interface rio / rc
License dual license (GNU GPLv2 and Lucent Public License)
Official website // .html/index/plan9.io9p (mirror)

Plan 9 from Bell Labs is a free distributed operating system. It was developed primarily for research purposes as the successor to Unix by the Computing Sciences Research Center at Bell Labs between the mid-1980s and 2002. Plan 9 continues to be used and developed by operating system researchers and hobbyists.[1][2]

Plan 9 has novel features such as the 9P protocol for accessing local and remote resources as files, union mounts, an improved proc file system, and native Unicode support throughout the system. In Plan 9, all system interfaces, including those required for networking and the user interface, are represented through the file system rather than specialized interfaces.

The name Plan 9 from Bell Labs is a reference to the Ed Wood 1959 cult science fiction Z-movie Plan 9 from Outer Space.[3] Also, Glenda, the Plan 9 Bunny, is presumably a reference to Wood's film Glen or Glenda.


  • History 1
  • Design concepts 2
    • 9P protocol 2.1
    • Union directories and namespaces 2.2
    • Special virtual filesystems 2.3
      • /proc 2.3.1
      • /net 2.3.2
    • Unicode 2.4
  • Combining the design concepts 3
  • Software for Plan 9 4
    • Graphical programs 4.1
    • Storage system 4.2
  • Unix compatibility 5
  • Impact 6
  • License 7
  • See also 8
  • References 9
  • External links 10


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[4]
2000 Plan 9 3rd ed. (Brazil) Released by Lucent Tech. under a gratis license for non-commercial use
2002 Plan 9 4th edition Released by Lucent Technologies under a new free software license

Plan 9 was a Bell Labs internal project from its start during the mid-1980s. It replaced Unix as Bell Labs's primary platform for operating systems research. It explored several changes to the original Unix model that facilitate the use and programming of the system, notably in distributed multi-user environments. In 1992, Bell Labs provided the first public release to universities, and three years later a commercial second release version became available to the general public. In the late 1990s, Lucent Technologies, having inherited Bell Labs, dropped commercial support for the project. In 2000, a non-commercial third release was distributed under an open source license. A fourth release under a new free software license occurred in 2002.[5]

A user and development community, including current and former Bell Labs members and Massachusetts Institute of Technology personnel, continues to produce minor daily releases in form of ISO images. Bell Labs still hosts the development.[6] The development source tree is accessible over the 9P and HTTP protocols and is used to update existing installations.[7] In addition to the official components of the OS included in the ISOs, Bell Labs also hosts a repository of externally developed applications and tools.

Plan 9 from Bell Labs was originally developed by members of the Computing Science Research Center at Bell Labs, the same group that originally developed UNIX and C.[8] The Plan 9 team was initially led by Rob Pike, Ken Thompson, Dave Presotto and Phil Winterbottom, with support from Dennis Ritchie as head of the Computing Techniques Research Department. Over the years, many notable developers have contributed to the project including Brian Kernighan, Tom Duff, Doug McIlroy, Bjarne Stroustrup and Bruce Ellis.[9]

Design concepts

Plan 9 from Bell Labs is like the Quakers: distinguished by its stress on the 'Inner Light,' noted for simplicity of life, in particular for plainness of speech. Like the Quakers, Plan 9 does not proselytize.

—Sape J. Mullender, Pierre G. Janson.
Real Time in a Real Operating System[10]

Plan 9 is an evolution of UNIX design concepts:[11]

  1. all objects are either files or file systems
  2. communication is over a network
  3. private namespaces allow their owners to access local and remote processes transparently

Plan 9 is a grid computing platform. It is an effort to provide a computing environment for geographically distributed clusters running on heterogeneous hardware, engineered for modern distributed environments and designed from the start to be a networked operating system.[12] It can be installed as a self-contained system and used on a single computer, but also has the capability to separate its components between separate computers. In a typical Plan 9 installation, users work at terminals running rio, and they access CPU servers which handle computation-intensive processes. Permanent data storage is provided by additional network hosts acting as file servers and archival storage.[13] Currently available desktop computers can emulate this architecture internally using multiple virtual machines.

9P protocol

To reduce the number of custom APIs and system calls, Plan 9 makes heavy use of the 9P protocol. 9P is a generic medium-agnostic byte-oriented protocol that provides for messages delivered between a server and a client.[14] The protocol is used to refer to and communicate with processes, programs, and data, including both the user interface and the network.[15] With the release of the 4th edition, it was modified and renamed 9P2000.[5]

Unlike most other operating systems, Plan 9 does not provide special application programming interfaces (such as Berkeley sockets, X resources or ioctl system calls) to access devices.[14] Instead, Plan 9 device drivers implement their control interface as a file system, so that the hardware can be accessed by the ordinary file input/output operations read and write. Consequently, sharing the device across the network can be accomplished by mounting the corresponding directory tree to the target machine.[3]

Union directories and namespaces

Plan 9 allows the user to collect the files (called names) from different directory trees in a single location. The name resolution is then performed from top to bottom: If the name doesn't exist in the top directory, it is looked up in lower ones until found. The same name in lower directories will be shown in the directory listing, but will not be accessible; thus, the merging of subdirectories is not handled.[16]

A union directory can be created by using the bind command:

; bind /arm/bin /bin
; bind -a /usr/inferno/Plan9/arm/bin /bin
; bind -b /usr/alice/bin /bin

In the example above, /arm/bin is mounted at /bin, the contents of /arm/bin replacing the previous contents of /bin. Inferno's bin directory is then union mounted after /bin, and Alice's personal bin directory is union mounted before. When a file is requested from /bin, it is first looked for in /usr/alice/bin, then in /arm/bin, and then finally in /usr/inferno/Plan9/arm/bin.

This mechanism of union directories replaces the search path of conventional UNIX shells. As far as you are concerned, all executable programs are in /bin.

Furthermore, the kernel can keep separate mount tables for each process,[10] and can thus provide each process with its own file system namespace. Processes' namespaces can be constructed independently, and the user may work simultaneously with programs that have heterogeneous namespaces.[18] Namespaces may be used to create an isolated environment similar to chroot, but in a more secure way.[14]

Plan 9's union directory architecture inspired BSD and Linux union file system implementations.[19]

Special virtual filesystems


Listing processes with list contents of directory (ls, lc) command[20] in /proc

Instead of having system calls specifically for process management, Plan 9 provides the /proc file system. Each process appears as a directory containing information and control files which can be manipulated by the ordinary file IO system calls.[16]

The file system approach allows Plan 9 processes to be managed with simple file management tools such as ls and cat; however, the processes cannot be copied and moved as files.[21]


Plan 9 does not have specialised system calls or ioctls for accessing the networking stack or networking hardware. Instead, the /net file system is used. Network connections are controlled by reading and writing control messages to control files. Sub-directories such as /net/tcp and /net/udp are used as an interface to their respective protocols.[21]


To reduce the complexity of managing character encodings, Plan 9 uses Unicode throughout the system. The initial Unicode implementation was ISO 10646. Ken Thompson invented UTF-8, which became the native encoding in Plan 9. The entire system was converted to general use in 1992.[22] UTF-8 preserves backwards compatibility with traditional null terminated strings, enabling more reliable information processing and the chaining of multilingual string data with Unix pipes between multiple processes. Using a single UTF-8 encoding with characters for all cultures and regions eliminates the need for switching between code sets.[23]

Combining the design concepts

Though interesting on their own, the design concepts of Plan 9 were supposed to be most useful when combined together. For example, to implement a network address translation (NAT) server, a union directory can be created, overlaying the router's /net directory tree with its own /net. Similarly, a virtual private network (VPN) can be implemented by overlaying in a union directory a /net hierarchy from a remote gateway, using secured 9P over the public Internet. A union directory with the /net hierarchy and filters can be used to sandbox an untrusted application or to implement a firewall.[14] In the same manner, a distributed computing network can be composed with a union directory of /proc hierarchies from remote hosts, which allows interacting with them as if they are local.

When used together, these features allow for assembling a complex distributed computing environment by reusing the existing hierarchical name system.[21]

Software for Plan 9

The distribution package for Plan 9 includes special compiler variants and programming languages, and provides a tailored set of libraries along with a windowing user interface system specific to Plan 9.[24] Its compiler is a dialect of C with some extensions and restrictions.[25]

As a benefit from the system's design, most tasks in Plan 9 can be accomplished by using ls, cat, grep, cp and rm utilities in combination with the rc shell (the default Plan 9 shell).

Factotum is an authentication and key management server for Plan 9. It handles authentication on behalf of other programs such that both secret keys and implementation details need only be known to Factotum.[26]

Graphical programs

Plan 9 running acme and rc

Unlike Unix, Plan 9 was designed with graphics in mind.[15] After booting, a Plan 9 terminal will run the rio windowing system, in which the user can create new windows displaying rc.[27] Graphical programs invoked from this shell replace it in its window.

The plumber provides an inter-process communication mechanism which allows system-wide hyperlinking.

Sam and acme are Plan 9's text editors.[28]

Storage system

Plan 9 supports the Kfs, Paq, Cwfs, FAT, and Fossil file systems. The latter was designed at Bell Labs specifically for Plan 9 and provides snapshot storage capability. It can be used directly with a hard drive or backed with Venti—an archival file system and permanent data storage system.

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. Still, many command line utilities of Plan 9 have aliases to the names of their Unix counterparts.[20]

Plan 9 can support POSIX applications and can emulate the Berkeley socket interface through the ANSI/POSIX Environment (APE) that implements an interface close to ANSI C and POSIX, with some common extensions (the native Plan 9 C interfaces conform to neither standard). It also includes a POSIX-compatible shell. APE's authors claim to have used it to port the X Window System (X11) to Plan 9, although they do not ship X11 "because supporting it properly is too big a job".[29] Some Linux binaries can be used with the help of a "linuxemu" (Linux emulator) application; however, it is still a work in progress.[30]


The wmii X window manager was inspired by acme, a text editor from the Plan 9 project.[31]

Plan 9 demonstrated that an integral concept of Unix—that every system interface could be represented as a set of files—could be successfully implemented in a modern distributed system.[27] Some features from Plan 9, like the UTF-8 character encoding of Unicode, have been implemented in other operating systems. Unix-like operating systems such as Linux have implemented 9P, Plan 9's file system, and limited forms of rfork-like system calls. Additionally, in Plan 9 from User Space, several of Plan 9's applications and tools, including the sam and acme editors, have been ported to Unix and Linux systems and have achieved some level of popularity. Several projects seek to replace the GNU operating system programs surrounding the Linux kernel with the Plan 9 operating system programs.[32][33] The 9wm window manager was inspired by , the older windowing system of Plan 9;[34] wmii is also heavily influenced by Plan 9.[31]

However, Plan 9 has never approached Unix in popularity, and has been primarily a research tool:

Plan 9 failed simply because it fell short of being a compelling enough improvement on Unix to displace its ancestor. Compared to Plan 9, Unix creaks and clanks and has obvious rust spots, but it gets the job done well enough to hold its position. There is a lesson here for ambitious system architects: the most dangerous enemy of a better solution is an existing codebase that is just good enough.

Other factors that contributed to low adoption of Plan 9 include the lack of commercial backup, the low number of end-user applications, and the lack of device drivers.[27][28]

Plan 9 proponents and developers claim that the problems hindering its adoption have been solved, that its original goals as a distributed system, development environment, and research platform have been met, and that it enjoys moderate but growing popularity. Inferno, through its hosted capabilities, has been a vehicle for bringing Plan 9 technologies to other systems as a hosted part of heterogeneous computing grids.[35][36][37][38]

Several projects actively work to extend Plan 9, including 9atom and 9front. These forks augment Plan 9 with additional hardware drivers and software, including nupas (an improved version of the Upas e-mail system), the go compiler, Mercurial version control system support, and other programs.[2][39] Plan 9 was ported to the Raspberry Pi single-board computer.[40][41]


Starting with the release of Fourth edition on April 2002,[5] the full source code of Plan 9 from Bell Labs was freely available under Lucent Public License 1.02, which is considered to be open source license by the Open Source Initiative (OSI), free software license by the Free Software Foundation, and it passes the Debian Free Software Guidelines.[14]

In February 2014 the University of California, Berkeley, has been authorised by the current Plan 9 copyright holderAlcatel-Lucent – to release all Plan 9 software previously governed by the Lucent Public License, Version 1.02 under the GNU General Public License, Version 2.[42]

See also


  1. ^ Robertson, James (2011-07-16). "Plan 9 Forked, Continues as 9front".  
  2. ^ a b "9atom". Retrieved 2011-11-11. 
  3. ^ a b c  
  4. ^ "Announcement of the first release to general public". 9 fans. 1995-07-16. 
  5. ^ a b c Loli-Queru, Eugenia (2002-04-29). "Bell Labs Releases New Version of Plan 9".  
  6. ^ "How to contribute". Bell Labs. Lucent Technologies. Retrieved 2011-11-30. 
  7. ^ "Staying up to date". Bell Labs. Lucent Technologies. Retrieved 2006-04-27. 
  8. ^ "From the inventors of UNIX system comes Plan 9 from Bell Labs" (Press release). Lucent Technologies. 1995-07-18. Archived from the original on 2006-02-09. 
  9. ^ McIlroy, Doug (Mar 1995). "Sys". Bell Labs (2nd ed.). Lucent Technologies. Retrieved 2006-04-02. 
  10. ^ a b Mullender, Sape J.; Janson, Pierre G. (2004-02-26). "Real Time in a Real Operating System". In Herbert, Andrew J.; Spärck Jones, Karen. Computer systems: theory, technology, and applications: a tribute to Roger Needham.  
  11. ^ Bischof, Hans-Peter; Imeyer, Gunter; Wellhöfer, Bernhard & Schreiner, Axel-Tobias (1999). Das Netzbetriebssystem Plan 9.  
  12. ^ Hancock, Brian (2003). "Reinventing Unix: an introduction to the Plan 9 operating system". Library Hi Tech (MCB UP) 21 (4): 471–76.  
  13. ^ Presotto, Dave;  
  14. ^ a b c d e Pereira, Uriel M. (2006). The Unix Spirit set Free: Plan 9 from Bell Labs ( 
  15. ^ a b Minnich, Ron (2005). "Why Plan 9 is not dead yet And What we can learn from it" (PDF).  
  16. ^ a b Ballesteros, Francisco J. (2007-09-28). "Introduction to OS abstractions using Plan 9 from Bell Labs" (pdf).  
  17. ^   Hosted by Mirtchovski.
  18. ^  
  19. ^ Valerie, Aurora (2009-03-25). "Union file systems: Implementations, part I".  
  20. ^ a b "UNIX to Plan 9 command translation". Bell Labs. Lucent Technologies. Retrieved 2011-12-02. 
  21. ^ a b c  
  22. ^  
  23. ^ Lunde, Ken (Jan 1999). CJKV information processing.  
  24. ^ Dixon, Rod (2004). Open source software law.  
  25. ^  
  26. ^ Cox, R.; Grosse, E.;  
  27. ^ a b c Hudson, Andrew (2006-07-19). "Investigating the Plan 9 Operating System".  
  28. ^ a b "An interview with Russ Cox". The Setup. Uses this. 2011-04-09. Retrieved 2012-01-01. 
  29. ^ Trickey, Howard. "APE – The ANSI/POSIX Environment". Bell Labs. Lucent Technologies. Retrieved 2011-04-27. 
  30. ^ "Linux emulation". Bell Labs. Lucent Technologies. Retrieved 2011-12-02. 
  31. ^ a b "window manager improved 2".  
  32. ^ "Glendix: Bringing the beauty of Plan 9 to Linux". Retrieved 2011-12-01. 
  33. ^ "Plan 9 From Gentoo: Plan 9 Meets Gentoo".  
  34. ^ "The 9wm Window Manager". 9wm. Retrieved 2012-01-02. 9wm is an X window manager which attempts to emulate the Plan 9 window manager 8-1/2 as far as possible within the constraints imposed by X. 
  35. ^ "9grid".  
  36. ^ "Vita Nuova Supplies Inferno Grid to Evotec OAI" (PDF) (Press release).  
  37. ^ "Rutgers University Libraries Install Inferno Data Grid" (PDF) (Press release).  
  38. ^ "The University of York Department of Biology install Vita Nuova's Inferno Data Grid" (PDF) (Press release).  
  39. ^ "plan9front – the front fell off". Retrieved 2011-12-01. 
  40. ^ Hayward, David (2013-05-09). "Raspberry Pi operating systems: 5 reviewed and rated".  
  41. ^ "How to install Plan 9 on a Raspberry Pi". eLinux. Retrieved 2014-11-16. 
  42. ^ Sharwood, Simon (2014-02-14). "Plan 9 moves out from Lucent licence space".  

External links

  • Official website
  • 9fans, the Plan 9 mailing list hosted by
  • Ninetimes Plan 9, Inferno, Unix, and Bell Labs operating systems news
  • #plan9, the Plan 9 IRC channel hosted by freenode
  • Random Contrarian Insurgent Organization, the Plan 9 user and developer community
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Hawaii eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.