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.\" from: @(#)fork.2 6.5 (Berkeley) 3/10/91 33.\" $Id: fork.2,v 1.5 1993/11/29 21:25:07 jtc Exp $ 34.\" 35.Dd March 10, 1991 36.Dt FORK 2 37.Os BSD 4.0 38.Sh NAME 39.Nm fork 40.Nd create a new process 41.Sh SYNOPSIS 42.Fd #include <sys/types.h> 43.Fd #include <unistd.h> 44.Ft pid_t 45.Fn fork void 46.Sh DESCRIPTION 47.Fn Fork 48causes creation of a new process. 49The new process (child process) is an exact copy of the 50calling process (parent process) except for the following: 51.Bl -bullet -offset indent 52.It 53The child process has a unique process ID. 54.It 55The child process has a different parent 56process ID (i.e., the process ID of the parent process). 57.It 58The child process has its own copy of the parent's descriptors. 59These descriptors reference the same underlying objects, so that, 60for instance, file pointers in file objects are shared between 61the child and the parent, so that an 62.Xr lseek 2 63on a descriptor in the child process can affect a subsequent 64.Xr read 65or 66.Xr write 67by the parent. 68This descriptor copying is also used by the shell to 69establish standard input and output for newly created processes 70as well as to set up pipes. 71.It 72The child processes resource utilizations 73are set to 0; see 74.Xr setrlimit 2 . 75.El 76.Sh RETURN VALUES 77Upon successful completion, 78.Fn fork 79returns a value 80of 0 to the child process and returns the process ID of the child 81process to the parent process. Otherwise, a value of -1 is returned 82to the parent process, no child process is created, and the global 83variable 84.Va errno 85is set to indicate the error. 86.Sh ERRORS 87.Fn Fork 88will fail and no child process will be created if: 89.Bl -tag -width Er 90.It Bq Er EAGAIN 91The system-imposed limit on the total 92number of processes under execution would be exceeded. 93This limit is configuration-dependent. 94.It Bq Er EAGAIN 95The system-imposed limit 96.Dv MAXUPRC 97.Pq Aq Pa sys/param.h 98on the total number of 99processes under execution by a single user would be exceeded. 100.It Bq Er ENOMEM 101There is insufficient swap space for the new process. 102.El 103.Sh SEE ALSO 104.Xr execve 2 , 105.Xr wait 2 106.Sh HISTORY 107A 108.Fn fork 109function call appeared in 110.At v6 . 111