392 lines
9.3 KiB
Text
392 lines
9.3 KiB
Text
.TH INTRO 1
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.SH NAME
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intro \- introduction to Plan 9
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.SH DESCRIPTION
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Plan 9 is a distributed computing environment assembled from
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separate machines acting as terminals,
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CPU servers, and file servers.
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A user works at a terminal, running a window system on a raster display.
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Some windows are connected to CPU servers; the intent is that heavy computing
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should be done in those windows but it is also possible to compute on the terminal.
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A separate file server provides file storage for terminals and
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CPU servers alike.
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.SS Name Spaces
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In Plan 9, almost all objects look like files.
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The object retrieved by a given name is determined by a mapping called the
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.IR "name space" .
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A quick tour of the standard name space is in
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.IR namespace (4).
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Every program running in Plan 9 belongs to a
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.I process group
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(see
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.I rfork
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in
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.IR fork (2)),
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and the name space for each process group can be independently
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customized.
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.PP
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A name space is hierarchically structured.
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A full file name (also called a
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.IR "full path name" )
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has the form
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.IP
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.RI / e1 / e2 /.../ en
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.PP
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This represents an object in a tree of files: the tree has a root,
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represented by the first
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.LR / ;
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the root has a child file named
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.IR e1 ,
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which in turn has child
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.IR e2 ,
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and so on; the descendent
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.I en
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is the object represented by the path name.
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.PP
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There are a number of Plan 9
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.I services
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available, each of which provides a tree of files.
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A name space is built by
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.I binding
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services (or subtrees of services) to names in the name-space-so-far.
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Typically, a user's home file server is bound to the root of the name space,
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and other services are bound to conventionally named subdirectories.
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For example, there is a service resident in the operating system for accessing
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hardware devices and that is bound to
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.B /dev
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by convention.
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Kernel services have names (outside the name space) that are a
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.L #
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sign followed by a single letter;
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for example,
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.B #c
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is conventionally bound to
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.BR /dev .
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.PP
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Plan 9 has
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.IR "union directories" :
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directories made of several directories all bound to the
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same name.
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The directories making up a union directory are ordered in a list.
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When the bindings are made
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(see
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.IR bind (1)),
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flags specify whether a newly bound member goes at the head or the tail of the list
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or completely replaces the list.
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To look up a name in a union directory, each member directory is searched
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in list order until the name is found.
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A bind
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flag specifies whether file creation is allowed in a member directory:
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a file created in the union directory goes in
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the first member directory in list order that allows creation, if any.
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.PP
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The glue that holds Plan 9 together is a network protocol called
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.IR 9P ,
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described in section 5 of this manual.
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All Plan 9 servers read and respond to 9P requests to navigate through
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a file tree and to perform operations such as reading and writing
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files within the tree.
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.SS Booting
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When a terminal is powered on or reset,
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it must be told the name of a file server to boot from,
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the operating system kernel to boot,
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and a user name and password.
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How this dialog proceeds is environment- and machine-dependent.
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Once it is complete,
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the terminal loads a Plan 9 kernel,
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which sets some environment variables (see
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.IR env (3))
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and builds an initial name space.
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See
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.IR namespace (4),
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.IR boot (8),
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and
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.IR init (8)
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for details, but some important aspects of the initial name space are:
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.IP \(bu
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The environment variable
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.B $cputype
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is set to the name of the kernel's CPU's architecture: one of
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.BR mips ,
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.BR sparc ,
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.B power
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(Power PC),
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.BR 386
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(386, 486, Pentium, ...)
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etc.
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The environment variable
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.B $objtype
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is initially the same as
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.BR $cputype .
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.IP \(bu
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The environment variable
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.B $terminal
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is set to a description of the machine running the kernel,
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such as
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.BR "generic pc" .
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Sometimes the middle word of
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.B $terminal
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encodes the file from which the kernel is booted.
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.IP \(bu
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The environment variable
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.B $service
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is set to
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.BR terminal .
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(Other ways of accessing Plan 9 may set
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.B $service
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to one of
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.BR cpu ,
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.BR con ,
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or
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.BR rx .)
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.IP \(bu
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The environment variable
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.B $user
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is set to the name of the user who booted the terminal.
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The environment variable
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.B $home
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is set to that user's home directory.
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.IP \(bu
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.B /$cputype/bin
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and
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.B /rc/bin
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are unioned into
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.BR /bin .
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.PD
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.PP
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After booting, the terminal runs the command interpreter,
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.IR rc (1),
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on
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.B /usr/$user/lib/profile
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after moving to the user's home directory.
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.PP
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Here is a typical profile:
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.IP
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.EX
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bind -a $home/bin/rc /bin
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bind -a $home/bin/$cputype /bin
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bind -c $home/tmp /tmp
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font = /lib/font/bit/pelm/euro.9.font
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upas/fs
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switch($service){
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case terminal
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plumber
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prompt=('term% ' ' ')
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exec rio -f $font
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case cpu
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bind /mnt/term/dev/cons /dev/cons
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bind /mnt/term/dev/consctl /dev/consctl
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bind -a /mnt/term/mnt/wsys /dev
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prompt=('cpu% ' ' ')
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news
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case con
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prompt=('cpu% ' ' ')
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news
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}
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.EE
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.PD
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.PP
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The first three lines replace
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.B /tmp
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with a
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.B tmp
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in the user's home directory
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and union personal
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.B bin
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directories with
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.BR /bin ,
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to be searched after the standard
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.B bin
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directories.
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The next starts the mail file system; see
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.IR mail (1).
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Then different things happen, depending on the
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.B $service
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environment variable,
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such as running the window system
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.IR rio (1)
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on a terminal.
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.PP
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To do heavy work such as compiling, the
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.IR rcpu (1)
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command connects a window to a CPU server;
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the same environment variables are set (to different values)
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and the same profile is run.
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The initial directory is the current directory in the terminal window
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where
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.I rcpu
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was typed.
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The value of
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.B $service
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will be
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.BR cpu ,
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so the second arm of the profile switch is executed.
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The root of the terminal's name space is accessible through
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.BR /mnt/term ,
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so the
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.I bind
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is a way of making the window system's graphics interface (see
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.IR draw (3))
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available to programs running on the CPU server.
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The
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.IR news (1)
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command reports current Plan 9 affairs.
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.PP
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The third possible service type,
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.BR con ,
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is set when the CPU server is called from a non-Plan-9 machine,
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such as through
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.I telnet
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(see
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.IR con (1)).
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.SS Using Plan 9
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The user commands of Plan 9 are reminiscent of those in Research Unix, version 10.
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There are a number of differences, however.
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.PP
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The standard shell is
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.IR rc (1),
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not the Bourne shell.
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The most noticeable differences appear only when programming and macro processing.
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.PP
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The character-delete character is backspace, and the line-kill character is
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control-U; these cannot be changed.
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.PP
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DEL is the interrupt character: typing it sends an interrupt to processes running in that window.
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See
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.IR keyboard (6)
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for instructions on typing characters like DEL on the various keyboards.
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.PP
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If a program dies with something like an address error, it enters a `Broken'
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state. It lingers, available for debugging with
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.IR db (1)
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or
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.IR acid (1).
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.I Broke
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(see
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.IR kill (1))
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cleans up broken processes.
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.PP
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The standard editor is one of
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.IR acme (1)
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or
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.IR sam (1).
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There is a variant of
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.I sam
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that permits running the file-manipulating part of
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.I sam
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on a non-Plan-9 system:
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.IP
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.EX
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sam -r tcp!kremvax
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.EE
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.PP
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For historical reasons,
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.I sam
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uses a tab stop setting of 8 spaces, while the other editors and window systems use 4 spaces.
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These defaults can be overridden by setting the value of the environment variable
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.B $tabstop
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to the desired number of spaces per tab.
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.PP
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Machine names may be prefixed by the network name,
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here
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.BR tcp ;
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and
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.B net
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for the system default.
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.PP
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Login connections and remote execution on non-Plan-9 machines are usually
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done by saying, for example,
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.IP
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.EX
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con kremvax
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.EE
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.PP
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or
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.IP
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.EX
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rx deepthought chess
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.EE
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.PP
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(see
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.IR con (1)).
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.PP
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.I 9fs
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connects to file systems of remote systems
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(see
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.IR srv (4)).
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For example,
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.IP
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.EX
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9fs kremvax
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.EE
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.PP
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sets things up so that the root of
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.BR kremvax 's
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file tree is visible locally in
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.BR /n/kremvax .
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.PP
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.IR Faces (1)
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gives graphical notification of arriving mail.
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.PP
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The Plan 9 file server has an integrated backup facility.
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The command
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.IP
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.EX
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9fs dump
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.EE
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.PP
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binds to
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.B /n/dump
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a tree containing the daily backups on the file server.
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The dump tree has years as top level file names, and month-day
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as next level file names.
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For example,
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.B /n/dump/2000/0120
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is the root of the file system as it appeared at dump time on
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January 20, 2000.
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If more than one dump is taken on the same day, dumps after
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the first have an extra digit.
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To recover the version of this file as it was on June 15, 1999,
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.IP
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.EX
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cp /n/dump/1999/0615/sys/man/1/0intro .
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.EE
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.PP
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or use
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.IR yesterday (1).
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.SH SEE ALSO
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This section for general publicly accessible commands.
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.br
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Section (2) for library functions, including system calls.
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.br
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Section (3) for kernel devices (accessed via
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.IR bind (1)).
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.br
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Section (4) for file services (accessed via
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.IR mount ).
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.br
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Section (5) for the Plan 9 file protocol.
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.br
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Section (6) for file formats.
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.br
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Section (7) for databases and database access programs.
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.br
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Section (8) for things related to administering Plan 9.
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.br
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.B /sys/doc
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for copies of papers referenced in this manual.
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.PP
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The back of this volume has a permuted index to aid searches.
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.SH DIAGNOSTICS
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Upon termination each program returns a string called the
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.IR "exit status" .
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It was either supplied by a call to
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.IR exits (2)
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or was written to the command's
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.BI /proc/ pid /note
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file
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(see
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.IR proc (3)),
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causing an abnormal termination.
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The empty string is customary for successful execution;
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a non-empty string gives a clue to the failure of the command.
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