1.\" $NetBSD: fork.2,v 1.14 2002/04/29 01:41:45 simonb 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 39.Sh NAME 40.Nm fork 41.Nd create a new process 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]unistd.h\*[Gt] 46.Ft pid_t 47.Fn fork void 48.Sh DESCRIPTION 49.Fn fork 50causes creation of a new process. 51The new process (child process) is an exact copy of the 52calling process (parent process) except for the following: 53.Bl -bullet -offset indent 54.It 55The child process has a unique process ID. 56.It 57The child process has a different parent 58process ID (i.e., the process ID of the parent process). 59.It 60The child process has its own copy of the parent's descriptors. 61These descriptors reference the same underlying objects, so that, 62for instance, file pointers in file objects are shared between 63the child and the parent, so that an 64.Xr lseek 2 65on a descriptor in the child process can affect a subsequent 66.Xr read 2 67or 68.Xr write 2 69by the parent. 70This descriptor copying is also used by the shell to 71establish standard input and output for newly created processes 72as well as to set up pipes. 73.It 74The child process' resource utilizations 75are set to 0; see 76.Xr setrlimit 2 . 77.El 78.Sh RETURN VALUES 79Upon successful completion, 80.Fn fork 81returns a value 82of 0 to the child process and returns the process ID of the child 83process to the parent process. 84Otherwise, a value of -1 is returned to the parent process, no 85child process is created, and the global variable 86.Va errno 87is set to indicate the error. 88.Sh ERRORS 89.Fn fork 90will fail and no child process will be created if: 91.Bl -tag -width [EAGAIN] 92.It Bq Er EAGAIN 93The system-imposed limit on the total 94number of processes under execution would be exceeded. 95This limit is configuration-dependent. 96.It Bq Er EAGAIN 97The limit 98.Dv RLIMIT_NPROC 99on the total number of 100processes under execution by this user id would be exceeded. 101.It Bq Er ENOMEM 102There is insufficient swap space for the new process. 103.El 104.Sh SEE ALSO 105.Xr execve 2 , 106.Xr setrlimit 2 , 107.Xr wait 2 108.Sh STANDARDS 109The 110.Fn fork 111function conforms to 112.St -p1003.1-90 . 113.Sh HISTORY 114A 115.Fn fork 116system call appeared in 117.At v6 . 118