1.\" $NetBSD: fork.2,v 1.10 1998/08/29 08:32:36 lukem 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 BSD 4 39.Sh NAME 40.Nm fork 41.Nd create a new process 42.Sh SYNOPSIS 43.Fd #include <sys/types.h> 44.Fd #include <unistd.h> 45.Ft pid_t 46.Fn fork void 47.Sh DESCRIPTION 48.Fn fork 49causes creation of a new process. 50The new process (child process) is an exact copy of the 51calling process (parent process) except for the following: 52.Bl -bullet -offset indent 53.It 54The child process has a unique process ID. 55.It 56The child process has a different parent 57process ID (i.e., the process ID of the parent process). 58.It 59The child process has its own copy of the parent's descriptors. 60These descriptors reference the same underlying objects, so that, 61for instance, file pointers in file objects are shared between 62the child and the parent, so that an 63.Xr lseek 2 64on a descriptor in the child process can affect a subsequent 65.Xr read 2 66or 67.Xr write 2 68by the parent. 69This descriptor copying is also used by the shell to 70establish standard input and output for newly created processes 71as well as to set up pipes. 72.It 73The child process' resource utilizations 74are set to 0; see 75.Xr setrlimit 2 . 76.El 77.Sh RETURN VALUES 78Upon successful completion, 79.Fn fork 80returns a value 81of 0 to the child process and returns the process ID of the child 82process to the parent process. 83Otherwise, a value of -1 is returned to the parent process, no 84child process is created, and the global variable 85.Va errno 86is set to indicate the error. 87.Sh ERRORS 88.Fn fork 89will fail and no child process will be created if: 90.Bl -tag -width [EAGAIN] 91.It Bq Er EAGAIN 92The system-imposed limit on the total 93number of processes under execution would be exceeded. 94This limit is configuration-dependent. 95.It Bq Er EAGAIN 96The limit 97.Dv RLIMIT_NPROC 98on the total number of 99processes under execution by this user id 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 setrlimit 2 , 106.Xr wait 2 107.Sh STANDARDS 108The 109.Fn fork 110function conforms to 111.St -p1003.1-90 . 112.Sh HISTORY 113A 114.Fn fork 115system call appeared in 116.At v6 . 117