1.\" $NetBSD: fork.2,v 1.12 1999/12/02 21:42:36 kleink 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 <sys/types.h> 46.Fd #include <unistd.h> 47.Ft pid_t 48.Fn fork void 49.Sh DESCRIPTION 50.Fn fork 51causes 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.El 79.Sh RETURN VALUES 80Upon successful completion, 81.Fn fork 82returns a value 83of 0 to the child process and returns the process ID of the child 84process to the parent process. 85Otherwise, a value of -1 is returned to the parent process, no 86child process is created, and the global variable 87.Va errno 88is set to indicate the error. 89.Sh ERRORS 90.Fn fork 91will fail and no child process will be created if: 92.Bl -tag -width [EAGAIN] 93.It Bq Er EAGAIN 94The system-imposed limit on the total 95number of processes under execution would be exceeded. 96This limit is configuration-dependent. 97.It Bq Er EAGAIN 98The limit 99.Dv RLIMIT_NPROC 100on the total number of 101processes under execution by this user id would be exceeded. 102.It Bq Er ENOMEM 103There is insufficient swap space for the new process. 104.El 105.Sh SEE ALSO 106.Xr execve 2 , 107.Xr setrlimit 2 , 108.Xr wait 2 109.Sh STANDARDS 110The 111.Fn fork 112function conforms to 113.St -p1003.1-90 . 114.Sh HISTORY 115A 116.Fn fork 117system call appeared in 118.At v6 . 119