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+.\" 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 4, 1993
+.Dt VFORK 2
+.Os BSD 4
+.Sh NAME
+.Nm vfork
+.Nd spawn new process in a virtual memory efficient way
+.Sh SYNOPSIS
+.Fd #include <unistd.h>
+.Ft int
+.Fn vfork void
+.Sh DESCRIPTION
+.Fn 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
+.Xr fork 2
+would have been to create a new system context for an
+.Xr execve .
+.Fn Vfork
+differs from
+.Xr fork
+in that the child borrows the parent's memory and thread of
+control until a call to
+.Xr execve 2
+or an exit (either by a call to
+.Xr exit 2
+or abnormally.)
+The parent process is suspended while the child is using its resources.
+.Pp
+.Fn Vfork
+returns 0 in the child's context and (later) the pid of the child in
+the parent's context.
+.Pp
+.Fn Vfork
+can normally be used just like
+.Xr fork .
+It does not work, however, to return while running in the childs context
+from the procedure that called
+.Fn vfork
+since the eventual return from
+.Fn vfork
+would then return to a no longer existent stack frame.
+Be careful, also, to call
+.Xr _exit
+rather than
+.Xr exit
+if you can't
+.Xr execve ,
+since
+.Xr exit
+will flush and close standard I/O channels, and thereby mess up the
+parent processes standard I/O data structures.
+(Even with
+.Xr fork
+it is wrong to call
+.Xr exit
+since buffered data would then be flushed twice.)
+.Sh SEE ALSO
+.Xr fork 2 ,
+.Xr execve 2 ,
+.Xr sigvec 2 ,
+.Xr wait 2 ,
+.Sh DIAGNOSTICS
+Same as for
+.Xr fork .
+.Sh BUGS
+This system call will be eliminated when proper system sharing
+mechanisms are implemented. 
+Users should not depend on the memory
+sharing semantics of
+.Xr vfork
+as it will, in that case, be made synonymous to
+.Xr fork .
+.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
+.Nm
+function call appeared in
+.Bx 3.0 .