term% ls -F
term% cat index.txt
PLUMBER(4)                 Kernel Interfaces Manual                 PLUMBER(4)

       plumber - file system for interprocess messaging

       plumber [ -p plumbing ]

       The  plumber  is  a  user-level  file  server  that receives, examines,
       rewrites, and dispatches plumb(6) messages between programs.   Its  be‐
       havior  is programmed by a plumbing file (default /usr/$user/lib/plumb‐
       ing) in the format of plumb(6).

       Its   services   are    mounted    on    the    directory    /mnt/plumb
       (/mnt/term/mnt/plumb  on the CPU server) and consist of two pre-defined
       files, send and rules, and a set of output ports for  dispatching  mes‐
       sages to applications.  The service is also published as a srv(4) file,
       named in $plumbsrv, for mounting elsewhere.

       Programs use write (see read(2)) to deliver messages to the send  file,
       and  read(2) to receive them from the corresponding port.  For example,
       sam(1)'s plumb menu item or the B command cause a message to be sent to
       /mnt/plumb/send; sam in turn reads from, by convention, /mnt/plumb/edit
       to receive messages about files to open.

       A copy of each message is sent to each client that has the  correspond‐
       ing port open.  If none has it open, and the rule has a plumb client or
       plumb start rule, that rule is applied.  A plumb client rule causes the
       specified  command  to  be  run and the message to be held for delivery
       when the port is opened.  A plumb start rule runs the command but  dis‐
       cards  the  message.   If  neither start or client is specified and the
       port is not open, the message is discarded and a  write  error  is  re‐
       turned to the sender.

       The  set of output ports is determined dynamically by the specification
       in the plumbing rules file: a port is created for each unique  destina‐
       tion of a plumb to rule.

       The  set  of rules currently active may be examined by reading the file
       /mnt/plumb/rules; appending to this file adds new  rules  to  the  set,
       while  creating  it (opening it with OTRUNC) clears the rule set.  Thus
       the rule set may be edited dynamically with a traditional text  editor.
       However,  ports  are  never  deleted dynamically; if a new set of rules
       does not include a port that was defined in earlier  rules,  that  port
       will still exist (although no new messages will be delivered there).

              default rules file

              directory to search for files in include statements

              mount point for plumber(4).


       plumb(1), plumb(2), plumb(6)

       Plumber's  file  name  space is fixed, so it is difficult to plumb mes‐
       sages that involve files in newly mounted services.