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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>

     int
     vfork(void);

DESCRIPTION
     Vfork() can be used to create new processes without fully copying the
     address space of the old process, which is	horrendously inefficient 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).  Vfork() 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.

     Vfork() returns 0 in the child's context and (later) the pid of the child
     in	the parent's context.

     Vfork() can normally be used just like fork(2).  It does not work,	how-
     ever, to return while running in the childs 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(2) 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() function 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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