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+.\"	$NetBSD: vfork.2,v 1.30 2021/06/09 06:00:16 nia 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. 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 9, 2021
+.Dt VFORK 2
+.Os
+.Sh NAME
+.Nm vfork
+.Nd spawn new process in a virtual memory efficient way
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft pid_t
+.Fn vfork void
+.Sh DESCRIPTION
+The
+.Nm
+system call creates a new process that does not have a new
+virtual address space, but rather shares address space with the
+parent, thus avoiding potentially expensive copy-on-write operations
+normally associated with creating a new process.
+It is useful when the purpose of
+.Xr fork 2
+would have been to create a new system context for an
+.Xr execve 2 .
+The
+.Nm
+system call differs from
+.Xr fork 2
+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
+The
+.Nm
+system call returns 0 in the child's context and (later) the pid
+of the child in the parent's context.
+.Pp
+The
+.Nm
+system call can normally be used just like
+.Xr fork 2 .
+It does not work, however, to return while running in the child's context
+from the procedure that called
+.Fn vfork
+since the eventual return from
+.Fn vfork
+would then return to a no longer existing stack frame.
+Be careful, also, to call
+.Xr _exit 2
+rather than
+.Xr exit 3
+if you can't
+.Xr execve 2 ,
+since
+.Xr exit 3
+will flush and close standard I/O channels, and thereby mess up the
+standard I/O data structures
+in the parent process.
+(Even with
+.Xr fork 2
+it is wrong to call
+.Xr exit 3
+since buffered data would then be flushed twice.)
+.Sh RETURN VALUES
+Same as for
+.Xr fork 2 .
+.Sh ERRORS
+Same as for
+.Xr fork 2 .
+.Sh SEE ALSO
+.Xr execve 2 ,
+.Xr fork 2 ,
+.Xr sigaction 2 ,
+.Xr wait 2 ,
+.Xr posix_spawn 3
+.Sh HISTORY
+The
+.Fn vfork
+function call appeared in
+.Bx 3.0 .
+In
+.Bx 4.4 ,
+the semantics were changed to only suspend the parent and not share
+the address space.
+The original semantics were reintroduced in
+.Nx 1.4 .
+.Sh BUGS
+Portable applications should not depend on the memory sharing
+semantics of
+.Fn vfork
+as implementations exist that implement
+.Fn vfork
+as plain
+.Xr fork 2 .
+.Pp
+To avoid a possible deadlock situation, processes that are children
+in the middle of a
+.Fn vfork
+are never sent
+.Dv SIGTSTP ,
+.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.
+.Pp
+New applications should prefer
+.Xr posix_spawn 3
+over
+.Nm
+followed by
+.Xr execve 2 .