1 .\" Copyright (c) 1980, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
12 .\" 3. Neither the name of the University nor the names of its contributors
13 .\" may be used to endorse or promote products derived from this software
14 .\" without specific prior written permission.
16 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 .\" @(#)vfork.2 8.1 (Berkeley) 6/4/93
36 .Nd create a new process without copying the address space
45 Since this function is hard to use correctly from application software,
46 it is recommended to use
56 can be used to create new processes without fully copying the address
57 space of the old process, which is inefficient in a paged
59 It is useful when the purpose of
61 would have been to create a new system context for an
68 in that the child borrows the parent process's address space and the
69 calling thread's stack
72 or an exit (either by a call to
75 The calling thread is suspended while the child is using its resources.
76 Other threads continue to run.
81 returns 0 in the child's context and (later) the pid of the child in
84 Many problems can occur when replacing
88 For example, it does not work to return while running in the child's context
89 from the procedure that called
91 since the eventual return from
93 would then return to a no longer existent stack frame.
94 Also, changing process state which is partially implemented in user space
95 such as signal handlers with
97 will corrupt the parent's state.
99 Be careful, also, to call
107 will flush and close standard I/O channels, and thereby mess up the
108 parent processes standard I/O data structures.
113 since buffered data would then be flushed twice.)
129 system call appeared in
132 To avoid a possible deadlock situation,
133 processes that are children in the middle
145 and input attempts result in an end-of-file indication.