INTRO(1)                                                 INTRO(1)

     NAME
          intro - introduction to Plan 9 from User Space

     DESCRIPTION
          Plan 9 is a distributed computing environment built at Bell
          Labs starting in the late 1980s.  The system can be obtained
          from Bell Labs at http://plan9.bell-labs.com/plan9 and runs
          on PCs and a variety of other platforms.  Plan 9 became a
          convenient platform for experimenting with new ideas, appli-
          cations, and services.

          Plan 9 from User Space provides many of the ideas, applica-
          tions, and services from Plan 9 on Unix-like systems.  It
          runs on FreeBSD (x86), Linux (x86 and PowerPC), Mac OS X
          (PowerPC), OpenBSD (x86), and SunOS (Sparc).

        Commands
          Plan 9 from User Space expects its own directory tree, con-
          ventionally /usr/local/plan9.  When programs need to access
          files in the tree, they expect the $PLAN9 environment vari-
          able to contain the name of the root of the tree.  See
          install(1) for details about installation.

          Many of the familiar Unix commands, for example cat(1),
          ls(1), and wc(1), are present, but in their Plan 9 forms:
          cat takes no options, ls does not columnate its output when
          printing to a terminal, and wc counts UTF characters.  In
          some cases, the differences are quite noticeable: grep(1)
          and sed(1) expect Plan 9 regular expressions (see
          regexp(7)), which are closest to what Unix calls extended
          regular expressions.  Because of these differences, it is
          not recommended to put $PLAN9/bin before the usual system
          bin directories in your search path.  Instead, put it at the
          end of your path and use the 9(1) script when you want to
          invoke the Plan 9 version of a traditional Unix command.

          Occasionally the Plan 9 programs have been changed to adapt
          to Unix.  Mk(1) now allows mkfiles to choose their own
          shell, and rc(1) has a ulimit builtin and manages $PATH.

          Many of the graphical programs from Plan 9 are present,
          including sam(1) and acme(1). An X11 window manager rio(1)
          mimics Plan 9's window system, with command windows imple-
          mented by the external program 9term(1). Following the style
          of X Windows, these programs run in new windows rather than
          the one in which they are invoked.  They all take a -W
          option to specify the size and placement of the new window.
          The argument is one of widthxheight, widthxheight@xmin,xmax,
          or xmin,ymin,xmax,ymax.

     INTRO(1)                                                 INTRO(1)

          The plumber(4) helps to connect the various Plan 9 programs
          together, and fittings like web(1) connect it to external
          programs such as web browsers; one can click on a URL in
          acme and see the page load in Firefox.

        User-level file servers
          In Plan 9, user-level file servers present file trees via
          the Plan 9 file protocol, 9P.  Processes can mount arbitrary
          file servers and customize their own name spaces.  These
          facilities are used to connect programs.  Clients interact
          with file servers by reading and writing files.

          This cannot be done directly on Unix.  Instead the servers
          listen for 9P connections on Unix domain sockets; clients
          connect to these sockets and speak 9P directly using the
          9pclient(3) library.  Intro(4) tells more of the story.  The
          effect is not as clean as on Plan 9, but it gets the job
          done and still provides a uniform and easy-to-understand
          mechanism.  The 9p(1) client can be used in shell scripts or
          by hand to carry out simple interactions with servers.
          Netfiles(1) is an experimental client for acme.

        External databases
          Some programs rely on large databases that would be cumber-
          some to include in every release.  Scripts are provided that
          download these databases separately.  These databases can be
          downloaded separately. See $PLAN9/dict/README and
          $PLAN9/sky/README.

        Programming
          The shell scripts 9c and 9l (see 9c(1)) provide a simple
          interface to the underlying system compiler and linker, sim-
          ilar to the 2c and 2l families on Plan 9.  9c compiles
          source files, and 9l links object files into executables.
          When using Plan 9 libraries, 9l infers the correct set of
          libraries from the object files, so that no -l options are
          needed.

          The only way to write multithreaded programs is to use the
          thread(3) library.  Rfork(3) exists but is not as capable as
          on Plan 9.  There are many unfortunate by necessary prepro-
          cessor diversions to make Plan 9 and Unix libraries coexist.
          See intro(3) for details.

          The debuggers acid(1) and db(1) and the debugging library
          mach(3) are works in progress.  They are platform-
          independent, so that x86 Linux core dumps can be inspected
          on PowerPC Mac OS X machines, but they are also fairly
          incomplete.  The x86 target is the most mature; initial Pow-
          erPC support exists; and other targets are unimplemented.
          The debuggers can only inspect, not manipulate, target pro-
          cesses.  Support for operating system threads and for 64-bit

     INTRO(1)                                                 INTRO(1)

          architectures needs to be rethought.  On x86 Linux systems,
          acid and db can be relied upon to produce reasonable stack
          traces (often in cases when GNU gdb cannot) and dump data
          structures, but that it is the extent to which they have
          been developed and exercised.

        Porting programs
          The vast majority of the familiar Plan 9 programs have been
          ported, including the Unicode-aware troff(1).

          Of the more recent additions to Plan 9, factotum(4),
          secstore(1), and secstored(1), vac(1), vacfs(4), and
          venti(8) are all ported.

          A backup system providing a dump file system built atop
          Venti is in progress; see vbackup(8).

        Porting to new systems
          Porting the tree to new operating systems or architectures
          should be straightforward, as system-specific code has been
          kept to a minimum. The largest pieces of system-specific
          code are <u.h>, which must include the right system files
          and set up the right integer type definitions, and
          libthread, which must implement spin locks, operating system
          thread creation, and context switching routines.  Portable
          implementations of these using <pthread.h> and <ucontext.h>
          already exist.  If your system supports them, you may not
          need to write any system specific code at all.

          There are other smaller system dependencies, such as the
          terminal handling code in 9term(1) and the implementation of
          getcallerpc(3), but these are usually simple and are not on
          the critical path for getting the system up and running.

     SEE ALSO
          The rest of this manual describes Plan 9 from User Space.
          Many of the man pages have been brought from Plan 9, but
          they have been updated, and others have been written from
          scratch.

          The manual pages are in a Unix style tree, with names like
          $PLAN9/man/man1/cat.1 instead of Plan 9's simpler
          $PLAN9/man/1/cat, so that the Unix man(1) utility can handle
          it.  Some systems, for example Debian Linux, deduce the man
          page locations from the search path, so that adding
          $PLAN9/bin to your path is sufficient to cause $PLAN9/man to
          be consulted for manual pages using the system man. On other
          systems, or to look at manual pages with the same name as a
          system page, invoke the Plan 9 man directly, as in 9 man
          cat.

          The manual sections follow the Unix numbering conventions,

     INTRO(1)                                                 INTRO(1)

          not the Plan 9 ones.

          describes general publicly accessible commands.

          describes C library functions.

          describes user-level file servers.

          describes file formats and protocols.  (On Unix, section (5)
          is technically for file formats but seems now to be used for
          describing specific files.)

          describes commands used for system administration.

          describes the Plan 9 file protocol 9P.

          These pages describe parts of the system that are new or
          different from Plan 9 from Bell Labs:

               9(1), 9c(1), 9p(1), 9term(1), acidtypes in acid(1),
               dial(1), hg(1), label(1), the MKSHELL variable in
               mk(1), namespace(1), netfiles(1), page(1), psfonts(1),
               rio(1), web(1), wintext(1)

               intro(3), 9pclient(3), the unix network in dial(3),
               exits(3), get9root(3), getns(3), notify(3),
               post9pservice(3), rfork(3), searchpath(3), sendfd(3),
               udpread(3), venti(3), wait(3), wctl(3)

               intro(4), 9pserve(4), import(4),

               vbackup(8)

               openfd(9p)

     DIAGNOSTICS
          In Plan 9, a program's exit status is an arbitrary text
          string, while on Unix it is an integer.  Section (1) of this
          manual describes commands as though they exit with string
          statuses.  In fact, exiting with an empty status corresponds
          to exiting with status 0, and exiting with any non-empty
          string corresponds to exiting with status 1.  See exits(3).