NetBSD/lib/libc/sys/vfork.2

.\"	$NetBSD: vfork.2,v 1.9 1997/11/01 06:37:50 mycroft Exp $
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.\"     @(#)vfork.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 30, 1997
.Dt VFORK 2
.Os BSD 4
.Sh NAME
.Nm vfork
.Nd spawn new process and block parent
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft pid_t
.Fn vfork void
.Sh DESCRIPTION
.Fn Vfork
was originally used to create new processes without fully copying the address
space of the old process, which is horrendously inefficient in a paged
environment.  It was useful when the purpose of
.Xr fork 2
would have been to create a new system context for an
.Xr execve .
It is the case that 
.Xr fork
is now efficient, even in the above case, so that the need for
.Fn vfork
is diminished.
.Fn Vfork
differs from
.Xr fork
in that the parent is suspended until the child makes a call to
.Xr execve 2
or an exit (either by a call to
.Xr _exit 2
or abnormally.)
.Pp
.Fn Vfork
returns 0 in the child's context and (later) the pid of the child in
the parent's context.
.Sh SEE ALSO
.Xr fork 2 ,
.Xr execve 2 ,
.Xr sigaction 2 ,
.Xr wait 2
.Sh DIAGNOSTICS
Same as for
.Xr fork 2 .
.Sh BUGS
.Pp
To avoid a possible deadlock situation,
processes that are children in the middle
of a
.Fn vfork
are never sent
.Dv SIGTTOU
or
.Dv SIGTTIN
signals; rather,
output or
.Xr ioctl 2
calls
are allowed
and input attempts result in an end-of-file indication.
.Sh HISTORY
The
.Fn vfork
function call appeared in
.Bx 3.0 .