1.\" $OpenBSD: vfork.2,v 1.20 2015/09/10 17:55:21 schwarze Exp $ 2.\" $NetBSD: vfork.2,v 1.8 1997/07/10 07:54:13 mikel Exp $ 3.\" 4.\" Copyright (c) 1980, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)vfork.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: September 10 2015 $ 34.Dt VFORK 2 35.Os 36.Sh NAME 37.Nm vfork 38.Nd spawn new process and block parent 39.Sh SYNOPSIS 40.In unistd.h 41.Ft pid_t 42.Fn vfork void 43.Sh DESCRIPTION 44.Fn vfork 45was originally used to create new processes without fully copying the address 46space of the old process, which is horrendously inefficient in a paged 47environment. 48It was useful when the purpose of 49.Xr fork 2 50would have been to create a new system context for an 51.Xr execve 2 . 52Since 53.Xr fork 2 54is now efficient, even in the above case, the need for 55.Fn vfork 56has diminished. 57.Fn vfork 58differs from 59.Xr fork 2 60in that the parent is suspended until the child makes a call to 61.Xr execve 2 62or an exit (either by a call to 63.Xr _exit 2 64or abnormally). 65In addition, fork handlers established using 66.Xr pthread_atfork 3 67are not called when a multithreaded program calls 68.Fn vfork . 69.Pp 70.Fn vfork 71returns 0 in the child's context and (later) the PID of the child in 72the parent's context. 73.Sh RETURN VALUES 74Same as for 75.Xr fork 2 . 76.Sh SEE ALSO 77.Xr execve 2 , 78.Xr fork 2 , 79.Xr sigaction 2 , 80.Xr wait 2 81.Sh HISTORY 82The 83.Fn vfork 84function call appeared in 85.Bx 3.0 86with the additional semantics that the child process ran in the 87memory of the parent until it called 88.Xr execve 2 89or exited. 90That sharing of memory was removed in 91.Bx 4.4 , 92leaving just the semantics of blocking the parent until the child calls 93.Xr execve 2 94or exits. 95On many other systems the original behavior has been restored, 96making this interface particularly unportable. 97.Sh BUGS 98To avoid a possible deadlock situation, processes that are children 99in the middle of a 100.Fn vfork 101are never sent 102.Dv SIGTTOU 103or 104.Dv SIGTTIN 105signals; rather, output or 106.Xr ioctl 2 107calls are allowed and input attempts result in an end-of-file indication. 108