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FORK(2)                       System Calls Manual                      FORK(2)



NAME
       fork, rfork - manipulate process resources

SYNOPSIS
       #include <u.h>
       #include <libc.h>

       int fork(void)

       int rfork(int flags)

DESCRIPTION
       Forking  is the only way new processes are created.  The flags argument
       to rfork selects which resources of the invoking process  (parent)  are
       shared  by the new process (child) or initialized to their default val‐
       ues.  The resources include the file name space, the open file descrip‐
       tor  table  (which,  when  shared,  permits processes to open and close
       files for other processes),  the  set  of  environment  variables  (see
       env(3)),  the note group (the set of processes that receive notes writ‐
       ten to a member's notepg file; see proc(3)), the set of rendezvous tags
       (see  rendezvous(2));  and open files.  Flags is the logical OR of some
       subset of

       RFPROC If set a new process is created; otherwise  changes  affect  the
              current process.

       RFNOWAIT
              If  set,  the child process will be dissociated from the parent.
              Upon exit the child will leave no Waitmsg (see wait(2)) for  the
              parent to collect.

       RFNAMEG
              If  set,  the  new  process inherits a copy of the parent's name
              space; otherwise the new process shares the parent's name space.
              Is mutually exclusive with RFCNAMEG.

       RFCNAMEG
              If  set,  the  new process starts with a clean name space. A new
              name space must be built from a mount of an open  file  descrip‐
              tor.  Is mutually exclusive with RFNAMEG.

       RFNOMNT
              If  set,  subsequent mounts into the new name space and derefer‐
              encing of pathnames starting with # are disallowed.

       RFENVG If set, the environment variables are copied; otherwise the  two
              processes  share  environment  variables.  Is mutually exclusive
              with RFCENVG.

       RFCENVG
              If set, the new process starts with an  empty  environment.   Is
              mutually exclusive with RFENVG.

       RFNOTEG
              Each  process  is  a  member  of  a  group of processes that all
              receive notes when a note is written  to  any  of  their  notepg
              files  (see  proc(3)).  The group of a new process is by default
              the same as its parent, but if RFNOTEG  is  set  (regardless  of
              RFPROC),  the process becomes the first in a new group, isolated
              from previous processes.

       RFFDG  If set, the invoker's file descriptor table  (see  intro(2))  is
              copied; otherwise the two processes share a single table.

       RFCFDG If  set, the new process starts with a clean file descriptor ta‐
              ble.  Is mutually exclusive with RFFDG.

       RFREND If set, the process will be unable to rendezvous(2) with any  of
              its ancestors; its children will, however, be able to rendezvous
              with it.  In effect, RFREND makes the process  the  first  in  a
              group of processes that share a space for rendezvous tags.

       RFMEM  If  set,  the  child and the parent will share data and bss seg‐
              ments.  Otherwise, the child inherits a copy of those  segments.
              Other segment types, in particular stack segments, will be unaf‐
              fected.  May be set only with RFPROC.

       File descriptors in a shared file descriptor table are kept open  until
       either  they  are  explicitly closed or all processes sharing the table
       exit.

       If RFPROC is set, the value returned  in  the  parent  process  is  the
       process  id  of  the  child process; the value returned in the child is
       zero.  Without RFPROC, the return value is  zero.   Process  ids  range
       from 1 to the maximum integer (int) value.  Rfork will sleep, if neces‐
       sary, until required process resources are available.

       Fork is just a call of rfork(RFFDG|RFREND|RFPROC).

SOURCE
       /sys/src/libc/9syscall
       /sys/src/libc/9sys/fork.c

SEE ALSO
       intro(2), proc(3),

DIAGNOSTICS
       These functions set errstr.



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