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Plan 9 - man page for fork (plan9 section 2)

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FORK(2) 										  FORK(2)

       fork, rfork - manipulate process resources

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

       int fork(void)

       int rfork(int flags)

       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.

	      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.

	      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.

	      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.

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

	      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).


       intro(2), proc(3),

       These functions set errstr.

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