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.\" 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 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd June 4, 1993 36.Dt FORK 2 37.Os 38.Sh NAME 39.Nm fork 40.Nd create a new process 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In sys/types.h 45.In unistd.h 46.Ft pid_t 47.Fn fork void 48.Sh DESCRIPTION 49The 50.Fn fork 51system call causes creation of a new process. 52The new process (child process) is an exact copy of the 53calling process (parent process) except for the following: 54.Bl -bullet -offset indent 55.It 56The child process has a unique process ID. 57.It 58The child process has a different parent 59process ID (i.e., the process ID of the parent process). 60.It 61The child process has its own copy of the parent's descriptors. 62These descriptors reference the same underlying objects, so that, 63for instance, file pointers in file objects are shared between 64the child and the parent, so that an 65.Xr lseek 2 66on a descriptor in the child process can affect a subsequent 67.Xr read 2 68or 69.Xr write 2 70by the parent. 71This descriptor copying is also used by the shell to 72establish standard input and output for newly created processes 73as well as to set up pipes. 74.It 75The child process' resource utilizations 76are set to 0; see 77.Xr setrlimit 2 . 78.It 79All interval timers are cleared; see 80.Xr setitimer 2 . 81.El 82.Sh RETURN VALUES 83Upon successful completion, 84.Fn fork 85returns a value 86of 0 to the child process and returns the process ID of the child 87process to the parent process. 88Otherwise, a value of -1 is returned 89to the parent process, no child process is created, and the global 90variable 91.Va errno 92is set to indicate the error. 93.Sh ERRORS 94The 95.Fn fork 96system call will fail and no child process will be created if: 97.Bl -tag -width Er 98.It Bq Er EAGAIN 99The system-imposed limit on the total 100number of processes under execution would be exceeded. 101The limit is given by the 102.Xr sysctl 3 103MIB variable 104.Dv KERN_MAXPROC . 105(The limit is actually ten less than this 106except for the super user). 107.It Bq Er EAGAIN 108The user is not the super user, and 109the system-imposed limit 110on the total number of 111processes under execution by a single user would be exceeded. 112The limit is given by the 113.Xr sysctl 3 114MIB variable 115.Dv KERN_MAXPROCPERUID . 116.It Bq Er EAGAIN 117The user is not the super user, and 118the soft resource limit corresponding to the 119.Fa resource 120argument 121.Dv RLIMIT_NPROC 122would be exceeded (see 123.Xr getrlimit 2 ) . 124.It Bq Er ENOMEM 125There is insufficient swap space for the new process. 126.El 127.Sh SEE ALSO 128.Xr execve 2 , 129.Xr rfork 2 , 130.Xr setitimer 2 , 131.Xr setrlimit 2 , 132.Xr vfork 2 , 133.Xr wait 2 134.Sh HISTORY 135The 136.Fn fork 137function appeared in 138.At v6 . 139