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VFORK(2)		  FreeBSD System Calls Manual		      VFORK(2)

NAME
     vfork -- spawn new	process	in a virtual memory efficient way

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION
     The vfork() system	call can be used to create new processes without fully
     copying the address space of the old process, which is horrendously inef-
     ficient in	a paged	environment.  It is useful when	the purpose of fork(2)
     would have	been to	create a new system context for	an execve(2).  The
     vfork() system call differs from fork(2) in that the child	borrows	the
     parent's memory and thread	of control until a call	to execve(2) or	an
     exit (either by a call to _exit(2)	or abnormally).	 The parent process is
     suspended while the child is using	its resources.

     The vfork() system	call returns 0 in the child's context and (later) the
     pid of the	child in the parent's context.

     The vfork() system	call can normally be used just like fork(2).  It does
     not work, however,	to return while	running	in the child's context from
     the procedure that	called vfork() since the eventual return from vfork()
     would then	return to a no longer existent stack frame.  Be	careful, also,
     to	call _exit(2) rather than exit(3) if you can't execve(2), since
     exit(3) will flush	and close standard I/O channels, and thereby mess up
     the parent	processes standard I/O data structures.	 (Even with fork(2) it
     is	wrong to call exit(3) since buffered data would	then be	flushed
     twice.)

SEE ALSO
     execve(2),	fork(2), rfork(2), sigvec(2), wait(2), _exit(2), exit(3)

RETURN VALUES
     Same as for fork(2).

BUGS
     This system call will be eliminated when proper system sharing mechanisms
     are implemented.  Users should not	depend on the memory sharing semantics
     of	vfork()	as it will, in that case, be made synonymous to	fork(2).

     To	avoid a	possible deadlock situation, processes that are	children in
     the middle	of a vfork() are never sent SIGTTOU or SIGTTIN signals;
     rather, output or ioctl(2)	calls are allowed and input attempts result in
     an	end-of-file indication.

HISTORY
     The vfork() system	call appeared in 2.9BSD.

FreeBSD	10.1			 June 4, 1993			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | SEE ALSO | RETURN VALUES | BUGS | HISTORY

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