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32 .\" @(#)vfork.2 8.1 (Berkeley) 6/4/93
33 .\" $FreeBSD: src/lib/libc/sys/vfork.2,v 1.12.2.6 2002/12/29 16:35:34 schweikh Exp $
34 .\" $DragonFly: src/lib/libc/sys/vfork.2,v 1.3 2006/02/17 19:35:06 swildner Exp $
41 .Nd spawn new process in a virtual memory efficient way
50 can be used to create new processes without fully copying the address
51 space of the old process, which is horrendously inefficient in a paged
52 environment. It is useful when the purpose of
54 would have been to create a new system context for an
59 in that the child borrows the parent's memory and thread of
60 control until a call to
62 or an exit (either by a call to
65 The parent process is suspended while the child is using its resources.
68 returns 0 in the child's context and (later) the pid of the child in
72 can normally be used just like
74 It does not work, however, to return while running in the child's context
75 from the procedure that called
77 since the eventual return from
79 would then return to a no longer existent stack frame.
80 Be careful, also, to call
88 will flush and close standard I/O channels, and thereby mess up the
89 parent processes standard I/O data structures.
94 since buffered data would then be flushed twice.)
109 function call appeared in
112 This system call will be eliminated when proper system sharing
113 mechanisms are implemented.
114 Users should not depend on the memory
117 as it will, in that case, be made synonymous to
120 To avoid a possible deadlock situation,
121 processes that are children in the middle
133 and input attempts result in an end-of-file indication.