Plan 9 from Bell Labs
Installation of Plan 9
|Company / developer||Bell Labs|
|Programmed in||Dialect of ANSI C|
|Source model||Free and open source software|
|Initial release||1992 (universities) / 1995 (general public)|
|Latest stable release||Fourth Edition / April 28, 2002|
|Latest unstable release||Snapshots / daily|
|Supported platforms||x86 / Vx32, x86-64, MIPS, DEC Alpha, SPARC, PowerPC, ARM|
|Default user interface||rio / rc|
|License||Lucent Public License|
Plan 9 from Bell Labs is a free software 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.
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. Also, Glenda, the Plan 9 Bunny, is presumably a reference to Wood's film Glen or Glenda.
|1992||Plan 9 1st Edition||Released by Bell Labs to universities|
|1995||Plan 9 2nd Edition||Released by Bell Labs for non-commercial purposes|
|2000||Plan 9 3rd Edition (Brazil)||Released by Lucent Technologies under an open source 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.
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. The development source tree is accessible over the 9P and HTTP protocols and is used to update existing installations. 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. 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.
Design concepts 
Plan 9 is an evolution of UNIX design concepts:
- all objects are either files or file systems
- communication is over a network
- 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. 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. 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. The protocol is used to refer to and communicate with processes, programs, and data, including both the user interface and the network. With the release of the 4th edition, it was modified and renamed 9P2000.
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. 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.
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.
A union directory can be created by using the
; 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 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
Furthermore, the kernel can keep separate mount tables for each process, 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. Namespaces may be used to create an isolated environment similar to chroot, but in a more secure way.
Special virtual filesystems 
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.
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/udp are used as an interface to their respective protocols.
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. 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.
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. 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.
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. Its compiler is a dialect of C with some extensions and restrictions.
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.
Graphical programs 
Unlike Unix, Plan 9 was designed with graphics in mind. After booting, a Plan 9 terminal will run the rio windowing system, in which the user can create new windows displaying rc. Graphical programs invoked from this shell replace it in its window.
Storage system 
Plan 9 supports the 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.
Plan 9 can support POSIX applications and can emulate the Berkeley socket interface through the ANSI/POSIX Environment (APE). Some Linux binaries can be used with the help of a "linuxemu" (Linux emulator) application; however, it is still a work in progress.
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. 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. The 9wm window manager was inspired by 8½, the older windowing system of Plan 9; wmii is also heavily influenced by Plan 9.
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.
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.
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.
The full source code is freely available under Lucent Public License 1.02; it is considered to be open source by the Open Source Initiative (OSI), free software by the Free Software Foundation, and it passes the Debian Free Software Guidelines.
See also 
- Alef (programming language)
- Amoeba (operating system)
- Glenda, the Plan 9 Bunny
- Rendezvous (Plan 9)
- Inferno (operating system)
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|Wikimedia Commons has media related to: Plan 9 (operating system)|
- Official website
- 9fans, the Plan 9 mailing list hosted by http://9fans.net
- Ninetimes Plan 9, Inferno, Unix, and Bell Labs operating systems news
- #plan9, the Plan 9 IRC channel hosted by freenode
- Cat-v.org Random Contrarian Insurgent Organization, the Plan 9 user and developer community