Plan 9 from Bell Laboratories FAQ

Newsgroups: comp.os.plan9,comp.os.misc,comp.answers,news.answers
From: (Steve Kotsopoulos)
Subject: Plan 9 from Bell Labs - Frequently Asked Questions [FAQ]
Summary: FAQ for the Plan 9 operating system
Organization: FYWSS
Expires: Apr 1, 2002
Followup-To: poster

Archive-name: comp-os/plan9-faq
Last-modified: Mar 3, 2002
Posting-Frequency: monthly

This document answers frequently asked questions about the third edition of the Plan 9 operating system. Much of it was rendered obsolete with the April/2002 release of Plan9 4th Edition, but it is being saved as a reference. It is unlikely to be updated anymore.

For up-to-date information, see

The following sections are new or modified recently:

A hypertext version of this FAQ is available on my Plan 9 web page, URL

Other sources of information include the newsgroup comp.os.plan9, which is bidirectionally gatewayed to the 9fans mailing list (browse archives at and, or mail to subscribe) and of course the Plan 9 homepage at Bell Labs, URL

If you'd like to discuss the Plan9 license, send mail to Mailing to this list subscribes you to the list.

Please forward any comments or suggestions regarding this FAQ to


Hardware and Software:

Installation and Administration:

General Information:


Subject: What is Plan 9?

Plan 9 is a new computer operating system and associated utilities. It was built by the Computing Science Research Center of Lucent Technologies Bell Laboratories, the same group that developed Unix, C, and C++.

Plan 9 is a distributed system. In the most general configuration, it uses three kinds of components: terminals that sit on users' desks, file servers that store permanent data, and other servers that provide faster CPUs, user authentication, and network gateways. These components are connected by various kinds of networks, including Ethernet, specially-built fiber networks, ordinary modem connections, and ISDN. In typical use, users interact with applications that run either on their terminals or on CPU servers, and the applications get their data from the file servers. The design, however, is highly configurable; it escapes from specific models of networked workstations and central machine service.

Subject: What is in the latest Plan9 release?

The press release for the third edition of Plan9 is at

Among the changes in this release of Plan 9 are a revised kernel, which now has the means to resolve ambiguous file names; an improved graphics environment; an updated command set; and expanded libraries. The system's creators also have installed "plumbing," a new mechanism for passing messages between interactive programs, as part of the user interface.

The new release is available for free download under an open source agreement. This is a significant step over previous releases.

If you'd like to browse the distribution packages before actually installing, you'll need the tools available at

Subject: For History Buffs

The first edition of Plan 9 was released in 1993, and was only available to universities.

In 1995 the second edition was available for purchase under a shrink-wrap license.

The second edition version of this FAQ is archived at

Subject: What is its relation to other operating systems?

Plan 9 is itself an operating system; it doesn't run as an application under another system. It was written from the ground up and doesn't include other people's code. Although the OS's interface to applications is strongly influenced by the approach of Unix, it's not a replacement for Unix; it is a new design.

Subject: What are its key ideas?

Plan 9 exploits, as far as possible, three basic technical ideas: first, all the system objects present themselves as named files that are manipulated by read/write operations; second, all these files may exist either locally or remotely, and respond to a standard protocol; third, the file system name space - the set of objects visible to a program - is dynamically and individually adjustable for each of the programs running on a particular machine. The first two of these ideas were foreshadowed in Unix and to a lesser extent in other systems, while the third is new: it allows a new engineering solution to the problems of distributed computing and graphics. Plan 9's approach means that application programs don't need to know where they are running; where, and on what kind of machine, to run a Plan 9 program is an economic decision that doesn't affect the construction of the application itself.

Subject: What are the advantages to this approach?

Plan 9's approach improves generality and modularity of application design by encouraging servers that make any kind of information appear to users and to applications just like collections of ordinary files. Here are a few examples.

The Plan 9 window system (called rio) is small and clean in part because its design is centered on providing a virtual keyboard, mouse, and screen to each of the applications running under it, while using the real keyboard, mouse, and screen supplied by the operating system. That is - besides creating, deleting, and arranging the windows themselves - its job is be a server for certain resources used by its clients. As a side benefit, this approach means that the window system can run recursively in one of its windows, or even on another machine.

Plan 9 users do Internet FTP by starting a local program that makes all the files on any FTP server (anywhere on the Internet) appear to be local files. Plan 9 PC users with a DOS/Windows partition on their disk can use the files stored there. ISO 9660 CD-ROMs and tar and cpio tapes all behave as if they were native file systems. The complete I/O behavior and performance of any application can be monitored by running it under a server that sees all its interactions. The debugger can examine a program on another machine even if it is running on a different hardware architecture.

Another example is the approach to networks. In Plan 9, each network presents itself as a set of files for connection creation, I/O, and control. A common semantic core for the operations is agreed upon, together with a general server for translating human-readable addresses to network-specific ones. As a result, applications don't care which kind of network (TCP/IP, ISDN, modem) they are using. In fact, applications don't even know whether the network they are using is physically attached to the machine the application is running on: the network interface files can be imported from another machine.

Hardware and Software:

Subject: What platforms does it run on?

The Plan 9 kernel and applications are highly portable. Plan 9 runs on four major machine architectures: Intel 386/486/Pentium, MIPS, Alpha, and PowerPC. Data structures and protocols are designed for distributed computing on machines of diverse design. Except for necessarily machine-dependent parts of the kernel, the compilers, and a few libraries, there is a single source representation for everything.

To find out whether Plan 9 supports your hardware, read The Various Ports and Supported PC Hardware.

Subject: Is anyone working on a port for my system?

Perhaps ... let us know.

Subject: Does it support symmetric multiprocessing?

Yes. The SGI Challenge series of multiprocessors and multi processor Pentiums are supported. Be warned that Intel-based SMP systems are notoriously fickle in conforming to the Multiprocessor Specification and often some head-scratching is required when things don't just work.

The system has been run on machines ranging from dual Pentium 90's up to quad Xeon 400's and the 8 processor Pentium Pro Axil system. By default, as it comes out the box, the release has SMP operation disabled by an option in the plan9.ini config file.

Subject: What about applications and tools?

Plan 9 comes with its own compilers for C and other languages, together with all the commands and program-development tools originally pioneered in the Unix environment. It also provides newly designed software. Acid is a programmable debugger that understands multiple-process programs, and the programs it is debugging may be running on a hardware platform different from its own. Acme is a new user interface in which any word on the screen can be interpreted as a command by clicking on it, and any string can specify a file to be displayed.

Subject: Is there a fortran compiler?

No, plan9 does not have a fortran compiler. If you have fortran programs you want to run, you can try using the f2c (fortran to C) converter available at

Subject: Where can I get more Plan 9 software?

Charles Forsyth has the original and still the largest list of software
Russ Cox has cd players, mp3 player and a wide variety of other small tools
Tad Hunt can help you balance your bank account, boot your laptop and listen to music
Nemo (Francisco Ballesteros) has a collection of drivers and utilities
Kenji Arisawa's ftp site
Boyd Roberts writes rc scripts when not ranting on 9fans
There's a native Python port at [based on Russ' port to 9P2000]
The wiki User-contributed Software page is useful too

Subject: Is it object-oriented?

No, not in the conventional sense. It is written in a strict dialect of ISO/ANSI C. In a wider sense, its general design of making all its `objects' look like files to which one talks in a well-defined protocol shows a related approach.

Subject: What about application portability?

Plan 9 comes with a library that makes it easy to import POSIX-conforming applications. There is also a library that emulates the Berkeley socket interface.

Subject: What resources does it need?

As might be expected, the answer depends on what you want to do. The kernel, the window system, and the basic applications will run comfortably on a PC with 8MB of memory.

On the other hand, the system can grow. The installation at Bell Laboratories includes multiprocessor SGI Challenge and Pentium machines as CPU servers, and a 350GB Sony WORM disk jukebox for the file server.

Subject: What GUIs does it support?

The standard interface doesn't use icons or drag-n-drop; Plan 9 people tend to be text-oriented. But the window system, the editor, and the general feel are very mousy, very point-and-click: Plan 9 windows are much more than a bunch of glass TTYs. The system supports the graphics primitives and libraries of basic software for building GUIs.
A screenshot is available at

Subject: How do I cut and paste with a 2 button mouse?

Plan 9 really works well only with a three-button mouse. In the meantime, Shift-Right-button will simulate a middle button, but that is inadequate for Acme's chording.

Subject: Does Plan 9 have any Unix-like terminal emulators?

The Plan 9 window system doesn't obey any inline cursor controls, since none of the native applications use cursor-addressing. All cursor control in rio, acme and sam is via the mouse.

To see some excellent articles on this important and divisive user interface issue read

If you want to get from Plan9 to Unix systems, you can run /bin/vt in one of your windows, telnet/rlogin to Unix, and set the term/TERM variable accordingly on the Unix end. See vt(1) for more details; note that vt(1) can emulate a VT100 VT220 or ANSI terminal.

Subject: What character set does it use?

The character set is Unicode, the 16-bit set unified with the ISO 10646 standard for representing languages used throughout the world. The system and its utilities support Unicode using a byte-stream representation (called UTF-8) that is compatible with ASCII. On Plan 9, one may grep for Cyrillic strings in a file with a Japanese name and see the results appear correctly on the terminal.

Subject: What about security and user authentication?

Plan 9's authentication design is akin to that of MIT's Kerberos. Passwords are never sent over networks; instead encrypted tickets are obtained from an authentication server. It doesn't have the concept of `set UID' programs. The file server doesn't run user programs, and except at its own console, it doesn't allow access to protected files except by authenticated owners. The concept of a special `root' user is gone.

Subject: How does it communicate with other systems?

The distribution includes a u9fs server that runs on Unix-compatible systems and understands the native Plan 9 remote file protocol, so that file systems of Unix machines may be imported into Plan 9. It also includes an NFS-compatible server that runs on Plan 9, so that Plan 9 file systems may be accessed from other systems that support NFS. It includes the full suite of Internet protocols (telnet, rlogin, ftp).

Subject: Is it suitable for real time control?

No, it is not. It is a general purpose system, without an interrupt priority scheme or real scheduler.

Installation and Administration:

Subject: What PC hardware works well with Plan 9?

If you don't want to spend time fiddling with and swapping PC hardware, you may prefer to buy hardware that is in use within Bell Labs, see Supported PC Hardware.

The biggest source of problems is getting the VGA configured on PC terminals. For best performance and functionality, it is recommended that you use a card that can run at 16 bits per pixel or greater, and with hardware-accelerated graphics support; currently only the Mach64 and S3 Virge are supported to this extent. The best buy today seems to be the ATI 8Meg Xpert 98 cards.

For a cpuserver or fileserver any old card that can do CGA is fine.

Subject: How do I Install Plan 9?

The installation is designed to be run from a PC.

  1. Read "Supported PC hardware" to ensure your PC meets the requirements.
  2. Back up your system.
  3. Make sure you've backed up your system.
  4. Read "Installing the Plan 9 Distribution" at URL
  5. Check the errata page at for problems and fixes found since the distribution was made.
  6. Here are some more questions that have been answered on the 9fans list:
IP configuration
ndb/cs will set the sysname if you setup an appropriate entry in /lib/ndb/local. You must specify an 'ether=' entry, and the address should be all lower case. If all goes well, ip/ipconfig will then configure IP.
Name Service
If you have having problems, first check that ndb/dns is running. It needs to be started in /rc/bin/termrc or /rc/bin/cpurc. Also note that only fully qualified names are supported, and there isn't a separate resolver.
Binding and Mounting Devices
Note that # is the shell comment character, so you must enclose it in single quotes. For example: bind -a '#R6' /dev
Auth Server
When booting a cpuserver without an auth server, if you give as the auth server address instead the cpu server's own address, you won't have to wait for it to timeout.

Subject: It doesn't work for me, how should I troubleshoot?

If you are having having SCSI problems, check your cables and terminators. this is generally the single largest cause of weird SCSI problems. Active terminators are best. If you run external cables you need to get high quality ones. Also, don't crank of the speed on the card.

Subject: How do I setup the VGA?

If the VGA doesn't work, read the last couple sections (Setting Up and Troubleshooting) of "Installing the Plan 9 Distribution"

You will have to find out more about the card so you can configure it. The relevant manuals are: vga(3), vgadb(6), vga(8), and 9load(8).

If your VGA card is not supported, you could try for Matrox G200 G400 and G450 drivers by Philippe Anel or see for Riva TNT drivers by Nicholas Waples.

(1st line) in plan9.ini and try again. It may not be of much help but will allow to ask a more specific question.

Subject: How do I control the services that start at boot time?

This is controlled by shell scripts, that are roughly equivalent to the /etc/rc files on Unix:
/rc/bin/termrc for terminals
/rc/bin/cpurc for cpu servers

See cpurc(8) for more details.

Subject: How do I setup network services?

For UDP services, you must start them up in the appropriate cpurc(8) file. For TCP or IL services, you must use the listen(8) daemon.

Subject: How do I shutdown my terminal/cpuserver system?

If you booted from a real fileserver, you can just turn it off.

If you are using kfs, you must halt the disks manually by typing
disk/kfscmd halt
at a prompt and waiting for ``kfs: file system halted'' to appear on the screen.

Not doing this means the disk might not be in a consistent state or modified data might not have been written out yet; not halting the disk forces the long wait at the ``kfs...'' when you boot the next time while kfs checks the disk.

Subject: How do I reboot my system?

The system can be rebooted by typing ^T^Tr (two control-T's followed by 'r'). Cpu servers can be rebooted by typing ^P on the console. See the cons(3) manual for more details.

General Information:

Subject: Where did the name come from?

It was chosen in the Bell Labs tradition of selecting names that make marketeers wince. The developers also wished to pay homage to the famous film, "Plan 9 From Outer Space".

Subject: How can I Obtain Plan 9?

The Plan 9 release is available for free download at
It includes source of the kernel, libraries, and commands for all supported architectures. It also includes complete binaries for the x86 architecture.

Subject: How can I get involved?

The best way to learn about the system is to write something that other people in the Plan 9 user community could use, or to port the system to new platforms.

Subject: Where can I get more detailed technical information?

The Bell Labs site stores a wealth of information about the system.
The manual pages are at
For auxiliary documentation, see
A Plan 9 wiki is maintained by enthusiasts at

Subject: Are there any Plan 9 user groups?

There is one in Austin, Texas. See It's open to anyone, even if you don't live in Austin.

Subject: Is the cross product of two vectors a vector?

No, it is not, and the fact that people treat it as one is the problem. The *geometric object* that is the closest thing to the c.p. is a skew tensor (practically the same as wedge product), which (only) in 3D has Cartesian components that resemble those of a vector, *except* that this pseudo-vector *flips* under reflection (unlike a genuine vector). Unfortunately, physicists have been trained to express Maxwell's laws as a relationship between a genuine vector (field) and a c.p., which means that that expression of those laws *changes* under reflection, something that physicists are *not* taught and which appears to have been overlooked in the analysis of the (nonconservation of) parity experiment.
I had to quote Douglas Gwyn verbatim on this, because I have no *ucking clue what he's talking about -- Steve

Subject: Can I emulate Plan 9 under Unix?

Ron Minnich has implemented private name spaces for Linux and FreeBSD. You can get documentation and source code from

Several Plan 9 inspired applications are available for Unix systems.

The sam editor is available from

There is also a Windows 95/NT version of Sam, currently distributed in binary form only, available from Comments and bug reports can be sent to

Wily is an acme lookalike by Gary Capell. See

Mark H. Wilkinson's 9libs package of Plan 9 emulation libraries for Unix is probably the easiest-to-install distribution of sam and wily. You can get it from

A free re-implementation of the rc shell is available from

9wm is David Hogan's lightweight X window manager in the style of 8½/rio. It was once available from but is being moved to a new home. Comments to

9term is an 8½ terminal emulator by Matty Farrow,, available from In the same directory, you'll find a collection of Unicode fonts that can be used with 9term, sam and wily.

9menu is a simple program by Arnold Robbins,, that allows you to create X menus from the shell, where each menu item will run a command. 9menu is intended for use with 9wm, but can be used with any other window manager. It is available from

Copyright © 1995 Lucent Technologies. All rights reserved.

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