1.\"	$MirOS: src/lib/libc/sys/vfork.2,v 1.3 2006/01/22 01:37:14 tg Exp $
2.\"	$OpenBSD: vfork.2,v 1.14 2003/06/02 20:18:39 millert Exp $
3.\"	$NetBSD: vfork.2,v 1.8 1997/07/10 07:54:13 mikel Exp $
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32.\"     @(#)vfork.2	8.1 (Berkeley) 6/4/93
33.\"
34.Dd June 30, 1997
35.Dt VFORK 2
36.Os
37.Sh NAME
38.Nm vfork
39.Nd spawn new process and block parent
40.Sh SYNOPSIS
41.Fd #include <unistd.h>
42.Ft pid_t
43.Fn vfork void
44.Sh DESCRIPTION
45.Fn vfork
46was originally used to create new processes without fully copying the address
47space of the old process, which is horrendously inefficient in a paged
48environment.
49It was useful when the purpose of
50.Xr fork 2
51would have been to create a new system context for an
52.Xr execve 2 .
53Since
54.Xr fork 2
55is now efficient, even in the above case, the need for
56.Fn vfork
57has diminished.
58.Fn vfork
59differs from
60.Xr fork 2
61in that the parent is suspended until the child makes a call to
62.Xr execve 2
63or an exit (either by a call to
64.Xr _exit 2
65or abnormally).
66.Pp
67.Fn vfork
68returns 0 in the child's context and (later) the PID of the child in
69the parent's context.
70.Sh RETURN VALUES
71Same as for
72.Xr fork 2 .
73.Sh SEE ALSO
74.Xr execve 2 ,
75.Xr fork 2 ,
76.Xr sigaction 2 ,
77.Xr wait 2
78.Sh HISTORY
79The
80.Fn vfork
81function call appeared in
82.Bx 2.9 .
83.Sh BUGS
84To avoid a possible deadlock situation, processes that are children
85in the middle of a
86.Fn vfork
87are never sent
88.Dv SIGTTOU
89or
90.Dv SIGTTIN
91signals; rather, output or
92.Xr ioctl 2
93calls are allowed and input attempts result in an end-of-file indication.
94