INTRO(1) General Commands Manual INTRO(1)
NAME
intro - introduction to Plan 9
DESCRIPTION
Plan 9 is a distributed computing environment assembled from separate machines acting as terminals, CPU servers, and file servers. A user
works at a terminal, running a window system on a bitmapped display. Some windows are connected to CPU servers; the intent is that heavy
computing should be done in those windows but it is also possible to compute on the terminal. A separate file server provides file storage
for terminals and CPU servers alike.
Name Spaces
In Plan 9, almost all objects look like files. The object retrieved by a given name is determined by a mapping called the name space. A
quick tour of the standard name space is in namespace(4). Every program running in Plan 9 belongs to a process group (see rfork in
fork(2)), and the name space for each process group can be independently customized.
A name space is hierarchically structured. A full file name (also called a full path name) has the form
/e1/e2/.../en
This represents an object in a tree of files: the tree has a root, represented by the first the root has a child file named e1, which in
turn has child e2, and so on; the descendent en is the object represented by the path name.
There are a number of Plan 9 services available, each of which provides a tree of files. A name space is built by binding services (or
subtrees of services) to names in the name-space-so-far. Typically, a user's home file server is bound to the root of the name space, and
other services are bound to conventionally named subdirectories. For example, there is a service resident in the operating system for
accessing hardware devices and that is bound to /dev by convention. Kernel services have names (outside the name space) that are a sign
followed by a single letter; for example, #c is conventionally bound to /dev.
Plan 9 has union directories: directories made of several directories all bound to the same name. The directories making up a union direc-
tory are ordered in a list. When the bindings are made (see bind(1)), flags specify whether a newly bound member goes at the head or the
tail of the list or completely replaces the list. To look up a name in a union directory, each member directory is searched in list order
until the name is found. A bind flag specifies whether file creation is allowed in a member directory: a file created in the union direc-
tory goes in the first member directory in list order that allows creation, if any.
The glue that holds Plan 9 together is a network protocol called 9P, described in section 5 of this manual. All Plan 9 servers read and
respond to 9P requests to navigate through a file tree and to perform operations such as reading and writing files within the tree.
Booting
When a terminal is powered on or reset, it must be told the name of a file server to boot from, the operating system kernel to boot, and a
user name and password. How this dialog proceeds is environment- and machine-dependent. Once it is complete, the terminal loads a Plan 9
kernel, which sets some environment variables (see env(3)) and builds an initial name space. See namespace(4), boot(8), and init(8) for
details, but some important aspects of the initial name space are:
o The environment variable $cputype is set to the name of the kernel's CPU's architecture: one of 68020, mips, sparc, or 386. The
environment variable $objtype is initially the same as $cputype.
o The environment variable $terminal is set to the model of the machine running the kernel: e.g., mips magnum 3000.
o The environment variable $service is set to terminal. (Other ways of accessing Plan 9 may set $service to one of cpu, con, or rx.)
o The environment variable $user is set to the name of the user who booted the terminal. The environment variable $home is set to
that user's home directory.
o /$cputype/bin and /rc/bin are unioned into /bin.
After booting, the terminal runs the command interpreter, rc(1), on /usr/$user/lib/profile after moving to the user's home directory.
Here is a typical profile:
bind -c $home/tmp /tmp
bind -a $home/bin/rc /bin
bind -a $home/bin/$cputype /bin
font = /lib/font/bit/pelm/euro.9.font
switch($service){
case terminal
prompt=('term% ' ' ')
exec 81/2 -f $font
case cpu
bind -b /mnt/term/mnt/81/2 /dev
prompt=('cpu% ' ' ')
news
case con
prompt=('cpu% ' ' ')
news
}
The first three lines replace /tmp with a tmp in the user's home directory and union personal bin directories with /bin, to be searched
after the standard bin directories. Then different things happen, depending on the $service environment variable, such as running the win-
dow system 81/2(1) on a terminal.
To do heavy work such as compiling, the cpu(1) command connects a window to a CPU server; the same environment variables are set (to dif-
ferent values) and the same profile is run. The initial directory is the current directory in the terminal window where cpu was typed.
The value of $service will be cpu, so the second arm of the profile switch is executed. The root of the terminal's name space is accessi-
ble through /mnt/term, so the bind is a way of making the window system's graphics interface (see bit(3)) available to programs running on
the CPU server. The news(1) command reports current Plan 9 affairs.
The third possible service type, con, is set when the CPU server is called from a non-Plan-9 machine, such as through telnet (see con(1)).
Using Plan 9
The user commands of Plan 9 are reminiscent of those in Research Unix, version 10; the window system is a lot like mux. There are a number
of differences, however.
The standard shell is rc(1), not the Bourne shell. The most noticeable differences appear only when programming and macro processing.
The character-delete character is backspace, and the line-kill character is control-U; these cannot be changed.
DEL is the interrupt character: typing it sends an interrupt to processes running in that window. See keyboard(6) for instructions on typ-
ing characters like DEL on the various keyboards.
If a program dies with something like an address error, it enters a `Broken' state. It lingers, available for debugging with db(1) or
acid(1). Broke (see kill(1)) cleans up broken processes.
The standard editor is sam(1). There is a variant that permits running the file-manipulating part of sam on a non-Plan-9 system:
sam -r tcp!kremvax
Machine names may be prefixed by the network name, here tcp; others include dk for Datakit and il for the Plan 9 Internet protocol.
Login connections and remote execution on non-Plan-9 machines are usually done by saying, for example,
con kremvax
or
rx deepthought chess
(see con(1)).
9fs connects to file systems of remote systems (see srv(4)). For example,
9fs kremvax
sets things up so that the root of kremvax's file tree is visible locally in /n/kremvax.
Seemail gives graphical notification of arriving mail (see mail(1)); if your mail arrives elsewhere, use vismon:
vismon tcp!kremvax
The Plan 9 file server has an integrated backup facility. The command
9fs dump
binds to /n/dump a tree containing the daily backups on the file server. The dump tree has years as top level file names, and month-day as
next level file names. For example, /n/dump/1990/0120 is the root of the file system as it appeared at dump time on January 20, 1990. If
more than one dump is taken on the same day, dumps after the first have an extra digit. To recover the version of this file as it was on
June 15, 1991,
cp /n/dump/1991/0615/sys/man/man1/Intro.1 .
or use yesterday(1).
SEE ALSO
This section for general publicly accessible commands.
Section (2) for library functions, including system calls.
Section (3) for kernel devices (accessed via bind(1)).
Section (4) for file services (accessed via mount).
Section (5) for the Plan 9 file protocol.
Section (6) for file formats.
Section (7) for databases and database access programs.
Section (8) for things related to administering Plan 9.
Section (9) for raster image software.
/sys/doc for copies of papers referenced in this manual.
The back of this volume has a permuted index to aid searches.
DIAGNOSTICS
Upon termination each program returns a string called the exit status. It was either supplied by a call to exits(2) or was written to the
command's /proc/pid/note file (see proc(3)), causing an abnormal termination. The empty string is customary for successful execution; a
non-empty string gives a clue to the failure of the command.
INTRO(1)