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.\" $NetBSD: vfork.2,v 1.8 1997/07/10 07:54:13 mikel Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)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 RETURN VALUES
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 2.9 .
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