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1 | .\" $NetBSD: fork.2,v 1.6 1995/02/27 12:32:36 cgd Exp $ |
2 | .\" | |
3 | .\" Copyright (c) 1980, 1991, 1993 | |
4 | .\" The Regents of the University of California. All rights reserved. | |
5 | .\" | |
6 | .\" Redistribution and use in source and binary forms, with or without | |
7 | .\" modification, are permitted provided that the following conditions | |
8 | .\" are met: | |
9 | .\" 1. Redistributions of source code must retain the above copyright | |
10 | .\" notice, this list of conditions and the following disclaimer. | |
11 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
12 | .\" notice, this list of conditions and the following disclaimer in the | |
13 | .\" documentation and/or other materials provided with the distribution. | |
14 | .\" 3. All advertising materials mentioning features or use of this software | |
15 | .\" must display the following acknowledgement: | |
16 | .\" This product includes software developed by the University of | |
17 | .\" California, Berkeley and its contributors. | |
18 | .\" 4. Neither the name of the University nor the names of its contributors | |
19 | .\" may be used to endorse or promote products derived from this software | |
20 | .\" without specific prior written permission. | |
21 | .\" | |
22 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
23 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
24 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
25 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
26 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
27 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
28 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
29 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
30 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
31 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
32 | .\" SUCH DAMAGE. | |
33 | .\" | |
34 | .\" @(#)fork.2 8.1 (Berkeley) 6/4/93 | |
35 | .\" | |
36 | .Dd June 4, 1993 | |
37 | .Dt FORK 2 | |
38 | .Os BSD 4 | |
39 | .Sh NAME | |
40 | .Nm fork | |
41 | .Nd create a new process | |
42 | .Sh SYNOPSIS | |
9bccf70c A |
43 | .Fd #include <unistd.h> |
44 | .Ft pid_t | |
2d21ac55 A |
45 | .Fo fork |
46 | .Fa void | |
47 | .Fc | |
9bccf70c | 48 | .Sh DESCRIPTION |
39037602 | 49 | .Fn fork |
9bccf70c A |
50 | causes creation of a new process. |
51 | The new process (child process) is an exact copy of the | |
52 | calling process (parent process) except for the following: | |
53 | .Bl -bullet -offset indent | |
54 | .It | |
55 | The child process has a unique process ID. | |
56 | .It | |
57 | The child process has a different parent | |
58 | process ID (i.e., the process ID of the parent process). | |
59 | .It | |
60 | The child process has its own copy of the parent's descriptors. | |
61 | These descriptors reference the same underlying objects, so that, | |
62 | for instance, file pointers in file objects are shared between | |
63 | the child and the parent, so that an | |
64 | .Xr lseek 2 | |
65 | on a descriptor in the child process can affect a subsequent | |
66 | .Xr read | |
67 | or | |
68 | .Xr write | |
69 | by the parent. | |
70 | This descriptor copying is also used by the shell to | |
71 | establish standard input and output for newly created processes | |
72 | as well as to set up pipes. | |
73 | .It | |
74 | The child processes resource utilizations | |
75 | are set to 0; see | |
76 | .Xr setrlimit 2 . | |
77 | .El | |
78 | .Sh RETURN VALUES | |
79 | Upon successful completion, | |
80 | .Fn fork | |
2d21ac55 A |
81 | returns a value of 0 to the child process |
82 | and returns the process ID of the child process to the parent process. | |
83 | Otherwise, a value of -1 is returned to the parent process, | |
84 | no child process is created, and the global variable | |
9bccf70c A |
85 | .Va errno |
86 | is set to indicate the error. | |
87 | .Sh ERRORS | |
39037602 | 88 | .Fn fork |
9bccf70c A |
89 | will fail and no child process will be created if: |
90 | .Bl -tag -width Er | |
2d21ac55 | 91 | .\" ========== |
9bccf70c | 92 | .It Bq Er EAGAIN |
2d21ac55 A |
93 | The system-imposed limit |
94 | on the total number of processes under execution | |
95 | would be exceeded. | |
9bccf70c | 96 | This limit is configuration-dependent. |
2d21ac55 | 97 | .\" ========== |
9bccf70c A |
98 | .It Bq Er EAGAIN |
99 | The system-imposed limit | |
100 | .Dv MAXUPRC | |
101 | .Pq Aq Pa sys/param.h | |
102 | on the total number of | |
103 | processes under execution by a single user would be exceeded. | |
2d21ac55 | 104 | .\" ========== |
9bccf70c A |
105 | .It Bq Er ENOMEM |
106 | There is insufficient swap space for the new process. | |
107 | .El | |
2d21ac55 A |
108 | .Sh LEGACY SYNOPSIS |
109 | .Fd #include <sys/types.h> | |
110 | .Fd #include <unistd.h> | |
111 | .Pp | |
112 | The include file | |
113 | .In sys/types.h | |
114 | is necessary. | |
9bccf70c A |
115 | .Sh SEE ALSO |
116 | .Xr execve 2 , | |
2d21ac55 A |
117 | .Xr sigaction 2 , |
118 | .Xr wait 2 , | |
119 | .Xr compat 5 | |
9bccf70c A |
120 | .Sh HISTORY |
121 | A | |
55e303ae | 122 | .Fn fork |
9bccf70c A |
123 | function call appeared in |
124 | .At v6 . | |
2d21ac55 A |
125 | .Sh CAVEATS |
126 | There are limits to what you can do in the child process. | |
127 | To be totally safe you should restrict yourself to only | |
128 | executing async-signal safe operations until such time | |
129 | as one of the exec functions is called. All APIs, including | |
130 | global data symbols, in any framework or library should be | |
131 | assumed to be unsafe after a | |
132 | .Fn fork | |
133 | unless explicitly documented to be safe or async-signal | |
134 | safe. If you need to use these frameworks in the child | |
135 | process, you must exec. In this situation it is reasonable | |
136 | to exec yourself. |