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1 | .\" Copyright (c) 1980, 1991 Regents of the University of California. |
2 | .\" 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 | .\" 3. All advertising materials mentioning features or use of this software | |
13 | .\" must display the following acknowledgement: | |
14 | .\" This product includes software developed by the University of | |
15 | .\" California, Berkeley and its contributors. | |
16 | .\" 4. Neither the name of the University nor the names of its contributors | |
17 | .\" may be used to endorse or promote products derived from this software | |
18 | .\" without specific prior written permission. | |
19 | .\" | |
20 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
21 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
22 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
23 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
24 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
25 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
26 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
27 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
28 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
29 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
30 | .\" SUCH DAMAGE. | |
31 | .\" | |
32 | .\" @(#)fork.2 6.5 (Berkeley) 3/10/91 | |
33 | .\" | |
34 | .Dd March 10, 1991 | |
35 | .Dt FORK 2 | |
36 | .Os BSD 4.0 | |
37 | .Sh NAME | |
38 | .Nm fork | |
39 | .Nd create a new process | |
40 | .Sh SYNOPSIS | |
41 | .Fd #include <unistd.h> | |
42 | .Ft pid_t | |
43 | .Fn fork void | |
44 | .Sh DESCRIPTION | |
45 | .Fn Fork | |
46 | causes creation of a new process. | |
47 | The new process (child process) is an exact copy of the | |
48 | calling process (parent process) except for the following: | |
49 | .Bl -bullet -offset indent | |
50 | .It | |
51 | The child process has a unique process ID. | |
52 | .It | |
53 | The child process has a different parent | |
54 | process ID (i.e., the process ID of the parent process). | |
55 | .It | |
56 | The child process has its own copy of the parent's descriptors. | |
57 | These descriptors reference the same underlying objects, so that, | |
58 | for instance, file pointers in file objects are shared between | |
59 | the child and the parent, so that an | |
60 | .Xr lseek 2 | |
61 | on a descriptor in the child process can affect a subsequent | |
62 | .Xr read | |
63 | or | |
64 | .Xr write | |
65 | by the parent. | |
66 | This descriptor copying is also used by the shell to | |
67 | establish standard input and output for newly created processes | |
68 | as well as to set up pipes. | |
69 | .It | |
70 | The child processes resource utilizations | |
71 | are set to 0; see | |
72 | .Xr setrlimit 2 . | |
73 | .El | |
74 | .Sh RETURN VALUES | |
75 | Upon successful completion, | |
76 | .Fn fork | |
77 | returns a value | |
78 | of 0 to the child process and returns the process ID of the child | |
79 | process to the parent process. Otherwise, a value of -1 is returned | |
80 | to the parent process, no child process is created, and the global | |
81 | variable | |
82 | .Va errno | |
83 | is set to indicate the error. | |
84 | .Sh ERRORS | |
85 | .Fn Fork | |
86 | will fail and no child process will be created if: | |
87 | .Bl -tag -width [EAGAIN] | |
88 | .It Bq Er EAGAIN | |
89 | The system-imposed limit on the total | |
90 | number of processes under execution would be exceeded. | |
91 | This limit is configuration-dependent. | |
92 | .It Bq Er EAGAIN | |
93 | The system-imposed limit | |
94 | .Dv MAXUPRC | |
95 | .Pq Aq Pa sys/param.h | |
96 | on the total number of | |
97 | processes under execution by a single user would be exceeded. | |
98 | .It Bq Er ENOMEM | |
99 | There is insufficient swap space for the new process. | |
100 | .El | |
101 | .Sh SEE ALSO | |
102 | .Xr execve 2 , | |
103 | .Xr wait 2 | |
104 | .Sh HISTORY | |
105 | A | |
106 | .Nm | |
107 | function call appeared in Version 6 AT&T UNIX. |