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     PROC(3)                                                   PROC(3)

     NAME
          proc - running processes

     SYNOPSIS
          bind #p /proc

          /proc/n/args
          /proc/n/ctl
          /proc/n/fd
          /proc/n/fpregs
          /proc/n/kregs
          /proc/n/mem
          /proc/n/note
          /proc/n/noteid
          /proc/n/notepg
          /proc/n/ns
          /proc/n/proc
          /proc/n/profile
          /proc/n/regs
          /proc/n/segment
          /proc/n/status
          /proc/n/text
          /proc/n/wait
          ...

     DESCRIPTION
          The proc device serves a two-level directory structure.  The
          first level contains numbered directories corresponding to
          pids of live processes; each such directory contains a set
          of files representing the corresponding process.

          The mem file contains the current memory image of the pro-
          cess.  A read or write at offset o, which must be a valid
          virtual address, accesses bytes from address o up to the end
          of the memory segment containing o. Kernel virtual memory,
          including the kernel stack for the process and saved user
          registers (whose addresses are machine-dependent), can be
          accessed through mem.  Writes are permitted only while the
          process is in the Stopped state and only to user addresses
          or registers.

          The read-only proc file contains the kernel per-process
          structure.  Its main use is to recover the kernel stack and
          program counter for kernel debugging.

          The files regs, fpregs, and kregs hold representations of
          the user-level registers, floating-point registers, and ker-
          nel registers in machine-dependent form.  The kregs file is
          read-only.

     PROC(3)                                                   PROC(3)

          The read-only fd file lists the open file descriptors of the
          process.  The first line of the file is its current direc-
          tory; subsequent lines list, one per line, the open files,
          giving the decimal file descriptor number; whether the file
          is open for read (r), write, (w), or both (rw); the type,
          device number, and qid of the file; its I/O offset; and its
          name at the time it was opened.

          The read-only ns file contains a textual representation of
          the process's file name space, in the format of namespace(6)
          accepted by newns (see auth(2)). The last line of the file
          identifies the current working directory of the process, in
          the form of a cd command (see rc(1)). The information in
          this file is based on the names files had when the name
          space was assembled, so the names it contains may be inac-
          cessible if the files have been subsequently renamed or
          rearranged.

          The read-only segment file contains a textual display of the
          memory segments attached to the process.  Each line has mul-
          tiple fields: the type of segment (Stack, Text, Data, Bss,
          etc.); one-letter flags such as R for read-only, if any;
          starting virtual address, in hexadecimal; ending virtual
          address, and reference count.

          The read-only status file contains a string with twelve
          fields, each followed by a space.  The fields are:

          -    the process name and user name, each 27 characters left
               justified

          -    the process state, 11 characters left justified (see
               ps(1))

          -    the six 11-character numbers also held in the process's
               #c/cputime file

          -    the amount of memory used by the process, except its
               stack, in units of 1024 bytes

          -    the base and current scheduling priority, each 11 char-
               acter numbers

          The read-only args file contains the arguments of the pro-
          gram when it was created by exec(2). If the program was not
          created by exec, such as by fork(2), its args file will be
          empty.  The format of the file is a list of quoted strings
          suitable for tokenize; see getfields(2).

          The text file is a pseudonym for the file from which the
          process was executed; its main use is to recover the symbol
          table of the process.

     PROC(3)                                                   PROC(3)

          The wait file may be read to recover Waitmsg records from
          the exiting children of the process.  If the process has no
          extant children, living or exited, a read of wait will
          block.  It is an error for a process to attempt to read its
          own wait file when it has no children.  When a process's
          wait file is being read, the process will draw an error if
          it attempts a wait system call; similarly, if a process is
          in a wait system call, its wait file cannot be read by any
          process.

          Textual messages written to the ctl file control the execu-
          tion of the process.  Some require that the process is in a
          particular state and return an error if it is not.

          stop      Suspend execution of the process, putting it in
                    the Stopped state.

          start     Resume execution of a Stopped process.

          waitstop  Do not affect the process directly but, like all
                    other messages ending with stop, block the process
                    writing the ctl file until the target process is
                    in the Stopped state or exits.  Also like other
                    stop control messages, if the target process would
                    receive a note while the message is pending, it is
                    instead stopped and the debugging process is
                    resumed.

          startstop Allow a Stopped process to resume, and then do a
                    waitstop action.

          hang      Set a bit in the process so that, when it com-
                    pletes an exec(2) system call, it will enter the
                    Stopped state before returning to user mode.  This
                    bit is inherited across a fork(2).

          closefiles
                    Close all open file descriptors in the process.

          nohang    Clear the hang bit.

          kill      Kill the process the next time it crosses the
                    user/kernel boundary.

          pri n     Set the base priority for the process to the inte-
                    ger n.

          wire n    Wire the process to processor n.

          The priority is interpreted by Plan 9's multilevel process
          scheduler.  Priorities run from 0 to 19, with higher numbers
          representing higher priorities.  A process has a base

     PROC(3)                                                   PROC(3)

          priority and a running priority which is less than or equal
          to the base priority.  As a process uses up more of its
          allocated time, its priority is lowered.  Unless explicitly
          set, user processes have base priority 10, kernel processes
          13.  Children inherit the parent's base priority.

          The read-only profile file contains the instruction fre-
          quency count information used for multiprocess profiling;
          see tprof in prof(1). The information is gleaned by sampling
          the program's user-level program counter at interrupt time.

          Strings written to the note file will be posted as a note to
          the process (see notify(2)). The note should be less than
          ERRLEN-1 characters long; the last character is reserved for
          a terminating NUL character.  A read of at least ERRLEN
          characters will retrieve the oldest note posted to the pro-
          cess and prevent its delivery to the process.  The notepg
          file is similar, but the note will be delivered to all the
          processes in the target process's note group (see fork(2)).
          However, if the process doing the write is in the group, it
          will not receive the note.  The notepg file is write-only.

          The textual noteid file may be read to recover an integer
          identifying the note group of the process (see RFNOTEG in
          fork(2)). The file may be written to cause the process to
          change to another note group, provided the group exists and
          is owned by the same user.

     FILES
          /sys/src/9/*/mem.h
          /sys/src/9/*/dat.h

     SEE ALSO
          debugger(2), mach(2), cons(3)

     SOURCE
          /sys/src/9/port/devproc.c