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1.1     ! root        1: .TH INTRO 1
        !             2: .SH NAME
        !             3: intro \- introduction to Plan 9
        !             4: .SH DESCRIPTION
        !             5: Plan 9 is a distributed computing environment assembled from
        !             6: separate machines acting as terminals,
        !             7: CPU servers, and file servers.
        !             8: A user works at a terminal, running a window system on a bitmapped display.
        !             9: Some windows are connected to CPU servers; the intent is that heavy computing
        !            10: should be done in those windows but it is also possible to compute on the terminal.
        !            11: A separate file server provides file storage for terminals and
        !            12: CPU servers alike.
        !            13: .SS Name Spaces
        !            14: In Plan 9, almost all objects look like files.
        !            15: The object retrieved by a given name is determined by a mapping called the
        !            16: .I name space.
        !            17: A quick tour of the standard name space is in
        !            18: .IR namespace (4).
        !            19: Every program running in Plan 9 belongs to a
        !            20: .I process group
        !            21: (see
        !            22: .I rfork
        !            23: in
        !            24: .IR fork (2)),
        !            25: and the name space for each process group can be independently
        !            26: customized.
        !            27: .PP
        !            28: A name space is hierarchically structured.
        !            29: A full file name (also called a
        !            30: .IR "full path name" )
        !            31: has the form
        !            32: .IP
        !            33: .RI / e1 / e2 /.../ en
        !            34: .PP
        !            35: This represents an object in a tree of files: the tree has a root,
        !            36: represented by the first
        !            37: .LR / ;
        !            38: the root has a child file named
        !            39: .IR e1 ,
        !            40: which in turn has child
        !            41: .IR e2 ,
        !            42: and so on; the descendent
        !            43: .I en
        !            44: is the object represented by the path name.
        !            45: .PP
        !            46: There are a number of Plan 9
        !            47: .I services
        !            48: available, each of which provides a tree of files.
        !            49: A name space is built by
        !            50: .I binding
        !            51: services (or subtrees of services) to names in the name-space-so-far.
        !            52: Typically, a user's home file server is bound to the root of the name space,
        !            53: and other services are bound to conventionally named subdirectories.
        !            54: For example, there is a service resident in the operating system for accessing
        !            55: hardware devices and that is bound to
        !            56: .B /dev
        !            57: by convention.
        !            58: Kernel services have names (outside the name space) that are a
        !            59: .L #
        !            60: sign followed by a single letter;
        !            61: for example,
        !            62: .B #c
        !            63: is conventionally bound to
        !            64: .BR /dev .
        !            65: .PP
        !            66: Plan 9 has
        !            67: .IR "union directories" :
        !            68: directories made of several directories all bound to the
        !            69: same name.
        !            70: The directories making up a union directory are ordered in a list.
        !            71: When the bindings are made
        !            72: (see
        !            73: .IR bind (1)),
        !            74: flags specify whether a newly bound member goes at the head or the tail of the list
        !            75: or completely replaces the list.
        !            76: To look up a name in a union directory, each member directory is searched
        !            77: in list order until the name is found.
        !            78: A bind
        !            79: flag specifies whether file creation is allowed in a member directory:
        !            80: a file created in the union directory goes in
        !            81: the first member directory in list order that allows creation, if any.
        !            82: .PP
        !            83: The glue that holds Plan 9 together is a network protocol called
        !            84: .IR 9P ,
        !            85: described in section 5 of this manual.
        !            86: All Plan 9 servers read and respond to 9P requests to navigate through
        !            87: a file tree and to perform operations such as reading and writing
        !            88: files within the tree.
        !            89: .SS Booting
        !            90: When a terminal is powered on or reset,
        !            91: it must be told the name of a file server to boot from,
        !            92: the operating system kernel to boot,
        !            93: and a user name and password.
        !            94: How this dialog proceeds is environment- and machine-dependent.
        !            95: Once it is complete,
        !            96: the terminal loads a Plan 9 kernel,
        !            97: which sets some environment variables (see
        !            98: .IR env (3))
        !            99: and builds an initial name space.
        !           100: See
        !           101: .IR namespace (4),
        !           102: .IR boot (8),
        !           103: and
        !           104: .IR init (8)
        !           105: for details, but some important aspects of the initial name space are:
        !           106: .IP \(bu
        !           107: The environment variable
        !           108: .B $cputype
        !           109: is set to the name of the kernel's CPU's architecture: one of
        !           110: .BR 68020 ,
        !           111: .BR mips ,
        !           112: .BR sparc ,
        !           113: or
        !           114: .BR 386 .
        !           115: The environment variable
        !           116: .B $objtype
        !           117: is initially the same as
        !           118: .BR $cputype .
        !           119: .IP \(bu
        !           120: The environment variable
        !           121: .B $terminal
        !           122: is set to the model of the machine running the kernel: e.g.,
        !           123: .BR "mips magnum 3000" .
        !           124: .IP \(bu
        !           125: The environment variable
        !           126: .B $service
        !           127: is set to
        !           128: .BR terminal .
        !           129: (Other ways of accessing Plan 9 may set
        !           130: .B $service
        !           131: to one of
        !           132: .BR cpu ,
        !           133: .BR con ,
        !           134: or
        !           135: .BR rx .)
        !           136: .IP \(bu
        !           137: The environment variable
        !           138: .B $user
        !           139: is set to the name of the user who booted the terminal.
        !           140: The environment variable
        !           141: .B $home
        !           142: is set to that user's home directory.
        !           143: .IP \(bu
        !           144: .B /$cputype/bin
        !           145: and
        !           146: .B /rc/bin
        !           147: are unioned into
        !           148: .BR /bin .
        !           149: .PD
        !           150: .PP
        !           151: After booting, the terminal runs the command interpreter,
        !           152: .IR rc (1),
        !           153: on
        !           154: .B /usr/$user/lib/profile
        !           155: after moving to the user's home directory.
        !           156: .PP
        !           157: Here is a typical profile:
        !           158: .IP
        !           159: .EX
        !           160: bind -c $home/tmp /tmp
        !           161: bind -a $home/bin/rc /bin
        !           162: bind -a $home/bin/$cputype /bin
        !           163: font = /lib/font/bit/pelm/euro.9.font
        !           164: switch($service){
        !           165: case terminal
        !           166:        prompt=('term% ' '      ')
        !           167:        exec 8½ -f $font
        !           168: case cpu
        !           169:        bind -b /mnt/term/mnt/8½ /dev
        !           170:        prompt=('cpu% ' '       ')
        !           171:        news
        !           172: case con
        !           173:        prompt=('cpu% ' '       ')
        !           174:        news
        !           175: }
        !           176: .EE
        !           177: .PD
        !           178: .PP
        !           179: The first three lines replace
        !           180: .B /tmp
        !           181: with a
        !           182: .B tmp
        !           183: in the user's home directory
        !           184: and union personal
        !           185: .B bin
        !           186: directories with
        !           187: .BR /bin ,
        !           188: to be searched after the standard
        !           189: .B bin
        !           190: directories.
        !           191: Then different things happen, depending on the
        !           192: .B $service
        !           193: environment variable,
        !           194: such as running the window system
        !           195: .IR 8½ (1)
        !           196: on a terminal.
        !           197: .PP
        !           198: To do heavy work such as compiling, the
        !           199: .IR cpu (1)
        !           200: command connects a window to a CPU server;
        !           201: the same environment variables are set (to different values)
        !           202: and the same profile is run.
        !           203: The initial directory is the current directory in the terminal window
        !           204: where
        !           205: .I cpu
        !           206: was typed.
        !           207: The value of
        !           208: .B $service
        !           209: will be
        !           210: .BR cpu ,
        !           211: so the second arm of the profile switch is executed.
        !           212: The root of the terminal's name space is accessible through
        !           213: .BR /mnt/term ,
        !           214: so the
        !           215: .I bind
        !           216: is a way of making the window system's graphics interface (see
        !           217: .IR bit (3))
        !           218: available to programs running on the CPU server.
        !           219: The
        !           220: .IR news (1)
        !           221: command reports current Plan 9 affairs.
        !           222: .PP
        !           223: The third possible service type,
        !           224: .BR con ,
        !           225: is set when the CPU server is called from a non-Plan-9 machine,
        !           226: such as through
        !           227: .I telnet
        !           228: (see
        !           229: .IR con (1)).
        !           230: .SS Using Plan 9
        !           231: The user commands of Plan 9 are reminiscent of those in Research Unix, version 10;
        !           232: the window system is a lot like
        !           233: .IR mux .
        !           234: There are a number of differences, however.
        !           235: .PP
        !           236: The standard shell is
        !           237: .IR rc (1),
        !           238: not the Bourne shell.
        !           239: The most noticeable differences appear only when programming and macro processing.
        !           240: .PP
        !           241: The character-delete character is backspace, and the line-kill character is
        !           242: control-U; these cannot be changed.
        !           243: .PP
        !           244: DEL is the interrupt character: typing it sends an interrupt to processes running in that window.
        !           245: See
        !           246: .IR keyboard (6)
        !           247: for instructions on typing characters like DEL on the various keyboards.
        !           248: .PP
        !           249: If a program dies with something like an address error, it enters a `Broken'
        !           250: state.  It lingers, available for debugging with
        !           251: .IR db (1)
        !           252: or
        !           253: .IR acid (1).
        !           254: .I Broke
        !           255: (see
        !           256: .IR kill (1))
        !           257: cleans up broken processes.
        !           258: .PP
        !           259: The standard editor is
        !           260: .IR sam (1).
        !           261: There is a variant that permits running the file-manipulating part of
        !           262: .I sam
        !           263: on a non-Plan-9 system:
        !           264: .IP
        !           265: .EX
        !           266: sam -r tcp!kremvax
        !           267: .EE
        !           268: .PP
        !           269: Machine names may be prefixed by the network name,
        !           270: here
        !           271: .BR tcp ;
        !           272: others include
        !           273: .B dk
        !           274: for Datakit and
        !           275: .B il
        !           276: for the Plan 9 Internet protocol.
        !           277: .PP
        !           278: Login connections and remote execution on non-Plan-9 machines are usually
        !           279: done by saying, for example,
        !           280: .IP
        !           281: .EX
        !           282: con kremvax
        !           283: .EE
        !           284: .PP
        !           285: or
        !           286: .IP
        !           287: .EX
        !           288: rx deepthought chess
        !           289: .EE
        !           290: .PP
        !           291: (see
        !           292: .IR con (1)).
        !           293: .PP
        !           294: .I 9fs 
        !           295: connects to file systems of remote systems
        !           296: (see
        !           297: .IR srv (4)).
        !           298: For example,
        !           299: .IP
        !           300: .EX
        !           301: 9fs kremvax
        !           302: .EE
        !           303: .PP
        !           304: sets things up so that the root of
        !           305: .BR kremvax 's
        !           306: file tree is visible locally in
        !           307: .BR /n/kremvax .
        !           308: .PP
        !           309: .I Seemail
        !           310: gives graphical notification of arriving mail
        !           311: (see
        !           312: .IR mail (1));
        !           313: if your mail arrives elsewhere, use
        !           314: .IR vismon :
        !           315: .IP
        !           316: .EX
        !           317: vismon tcp!kremvax
        !           318: .EE
        !           319: .PP
        !           320: The Plan 9 file server has an integrated backup facility.
        !           321: The command
        !           322: .IP
        !           323: .EX
        !           324: 9fs dump
        !           325: .EE
        !           326: .PP
        !           327: binds to
        !           328: .B /n/dump
        !           329: a tree containing the daily backups on the file server.
        !           330: The dump tree has years as top level file names, and month-day
        !           331: as next level file names.
        !           332: For example,
        !           333: .B /n/dump/1990/0120
        !           334: is the root of the file system as it appeared at dump time on
        !           335: January 20, 1990.
        !           336: If more than one dump is taken on the same day, dumps after
        !           337: the first have an extra digit.
        !           338: To recover the version of this file as it was on June 15, 1991,
        !           339: .IP
        !           340: .EX
        !           341: cp /n/dump/1991/0615/sys/man/man1/Intro.1 .
        !           342: .EE
        !           343: .PP
        !           344: or use
        !           345: .IR yesterday (1).
        !           346: .SH SEE ALSO
        !           347: This section for general publicly accessible commands.
        !           348: .br
        !           349: Section (2) for library functions, including system calls.
        !           350: .br
        !           351: Section (3) for kernel devices (accessed via
        !           352: .IR bind (1)).
        !           353: .br
        !           354: Section (4) for file services (accessed via
        !           355: .IR mount ).
        !           356: .br
        !           357: Section (5) for the Plan 9 file protocol.
        !           358: .br
        !           359: Section (6) for file formats.
        !           360: .br
        !           361: Section (7) for databases and database access programs.
        !           362: .br
        !           363: Section (8) for things related to administering Plan 9.
        !           364: .br
        !           365: Section (9) for raster image software.
        !           366: .br
        !           367: .B /sys/doc
        !           368: for copies of papers referenced in this manual.
        !           369: .PP
        !           370: The back of this volume has a permuted index to aid searches.
        !           371: .SH DIAGNOSTICS
        !           372: Upon termination each program returns a string called the
        !           373: .IR "exit status" .
        !           374: It was either supplied by a call to
        !           375: .IR exits (2)
        !           376: or was written to the command's
        !           377: .BI /proc/ pid /note
        !           378: file
        !           379: (see
        !           380: .IR proc (3)),
        !           381: causing an abnormal termination.
        !           382: The empty string is customary for successful execution;
        !           383: a non-empty string gives a clue to the failure of the command.

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