Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
VFORK(2)		  FreeBSD System Calls Manual		      VFORK(2)

NAME
     vfork -- create a new process without copying the address space

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 cannot	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.)

RETURN VALUES
     Same as for fork(2).

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

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

BUGS
     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.

FreeBSD	10.1		       November	13, 2009		  FreeBSD 10.1

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

Want to link to this manual page? Use this URL:
<http://www.freebsd.org/cgi/man.cgi?query=vfork&sektion=2&manpath=FreeBSD+9.1-RELEASE>

home | help