1.\" Copyright (c) 1980, 1991, 1993
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
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.\" 4. 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.
15.\"
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
26.\" SUCH DAMAGE.
27.\"
28.\" @(#)vfork.2 8.1 (Berkeley) 6/4/93
29.\" $FreeBSD: head/lib/libc/sys/vfork.2 165903 2007-01-09 00:28:16Z imp $
30.\"
31.Dd June 4, 1993
32.Dt VFORK 2
33.Os
34.Sh NAME
35.Nm vfork
36.Nd spawn new process in a virtual memory efficient way
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In unistd.h
41.Ft pid_t
42.Fn vfork void
43.Sh DESCRIPTION
44The
45.Fn vfork
46system call
47can be used to create new processes without fully copying the address
48space of the old process, which is horrendously inefficient in a paged
49environment.
50It is useful when the purpose of
51.Xr fork 2
52would have been to create a new system context for an
53.Xr execve 2 .
54The
55.Fn vfork
56system call
57differs from
58.Xr fork 2
59in that the child borrows the parent's memory and thread of
60control until a call to
61.Xr execve 2
62or an exit (either by a call to
63.Xr _exit 2
64or abnormally).
65The parent process is suspended while the child is using its resources.
66.Pp
67The
68.Fn vfork
69system call
70returns 0 in the child's context and (later) the pid of the child in
71the parent's context.
72.Pp
73The
74.Fn vfork
75system call
76can normally be used just like
77.Xr fork 2 .
78It does not work, however, to return while running in the child's context
79from the procedure that called
80.Fn vfork
81since the eventual return from
82.Fn vfork
83would then return to a no longer existent stack frame.
84Be careful, also, to call
85.Xr _exit 2
86rather than
87.Xr exit 3
88if you cannot
89.Xr execve 2 ,
90since
91.Xr exit 3
92will flush and close standard I/O channels, and thereby mess up the
93parent processes standard I/O data structures.
94(Even with
95.Xr fork 2
96it is wrong to call
97.Xr exit 3
98since buffered data would then be flushed twice.)
99.Sh RETURN VALUES
100Same as for
101.Xr fork 2 .
102.Sh SEE ALSO
103.Xr execve 2 ,
104.Xr _exit 2 ,
105.Xr fork 2 ,
106.Xr rfork 2 ,
107.Xr sigvec 2 ,
108.Xr wait 2 ,
109.Xr exit 3
110.Sh HISTORY
111The
112.Fn vfork
113system call appeared in
114.Bx 2.9 .
115.Sh BUGS
116This system call will be eliminated when proper system sharing
117mechanisms are implemented.
118Users should not depend on the memory
119sharing semantics of
120.Fn vfork
121as it will, in that case, be made synonymous to
122.Xr fork 2 .
123.Pp
124To avoid a possible deadlock situation,
125processes that are children in the middle
126of a
127.Fn vfork
128are never sent
129.Dv SIGTTOU
130or
131.Dv SIGTTIN
132signals; rather,
133output or
134.Xr ioctl 2
135calls
136are allowed
137and input attempts result in an end-of-file indication.
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
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.\" 4. 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.
15.\"
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
26.\" SUCH DAMAGE.
27.\"
28.\" @(#)vfork.2 8.1 (Berkeley) 6/4/93
29.\" $FreeBSD: head/lib/libc/sys/vfork.2 165903 2007-01-09 00:28:16Z imp $
30.\"
31.Dd June 4, 1993
32.Dt VFORK 2
33.Os
34.Sh NAME
35.Nm vfork
36.Nd spawn new process in a virtual memory efficient way
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In unistd.h
41.Ft pid_t
42.Fn vfork void
43.Sh DESCRIPTION
44The
45.Fn vfork
46system call
47can be used to create new processes without fully copying the address
48space of the old process, which is horrendously inefficient in a paged
49environment.
50It is useful when the purpose of
51.Xr fork 2
52would have been to create a new system context for an
53.Xr execve 2 .
54The
55.Fn vfork
56system call
57differs from
58.Xr fork 2
59in that the child borrows the parent's memory and thread of
60control until a call to
61.Xr execve 2
62or an exit (either by a call to
63.Xr _exit 2
64or abnormally).
65The parent process is suspended while the child is using its resources.
66.Pp
67The
68.Fn vfork
69system call
70returns 0 in the child's context and (later) the pid of the child in
71the parent's context.
72.Pp
73The
74.Fn vfork
75system call
76can normally be used just like
77.Xr fork 2 .
78It does not work, however, to return while running in the child's context
79from the procedure that called
80.Fn vfork
81since the eventual return from
82.Fn vfork
83would then return to a no longer existent stack frame.
84Be careful, also, to call
85.Xr _exit 2
86rather than
87.Xr exit 3
88if you cannot
89.Xr execve 2 ,
90since
91.Xr exit 3
92will flush and close standard I/O channels, and thereby mess up the
93parent processes standard I/O data structures.
94(Even with
95.Xr fork 2
96it is wrong to call
97.Xr exit 3
98since buffered data would then be flushed twice.)
99.Sh RETURN VALUES
100Same as for
101.Xr fork 2 .
102.Sh SEE ALSO
103.Xr execve 2 ,
104.Xr _exit 2 ,
105.Xr fork 2 ,
106.Xr rfork 2 ,
107.Xr sigvec 2 ,
108.Xr wait 2 ,
109.Xr exit 3
110.Sh HISTORY
111The
112.Fn vfork
113system call appeared in
114.Bx 2.9 .
115.Sh BUGS
116This system call will be eliminated when proper system sharing
117mechanisms are implemented.
118Users should not depend on the memory
119sharing semantics of
120.Fn vfork
121as it will, in that case, be made synonymous to
122.Xr fork 2 .
123.Pp
124To avoid a possible deadlock situation,
125processes that are children in the middle
126of a
127.Fn vfork
128are never sent
129.Dv SIGTTOU
130or
131.Dv SIGTTIN
132signals; rather,
133output or
134.Xr ioctl 2
135calls
136are allowed
137and input attempts result in an end-of-file indication.