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 values.  The resources include the file name  space,  the	open  file
       descriptor 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 written to a member's notepg file; see proc(3)), 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 par-
	      ent 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.   The
	      tag space for rendezvous(2) is considered part of the 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 descriptor.	Is
	      mutually exclusive with RFNAMEG.

       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 table.  Is mutually exclusive with RFFDG.

       RFMEM  If set, the kernel will mark segments of type data and bss as shared. The child will then inherit all the shared segments the parent
	      process owns. Other segment types will be unaffected.  Subsequent forks by the parent will then propagate the shared  data  and  bss
	      between children.  The stack segment is always split.  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 necessary,
       until required process resources are available.

       Fork is just a call of rfork(RFFDG|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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