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	1	.\" $NetBSD: fork.2,v 1.6 1995/02/27 12:32:36 cgd 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
	49	causes creation of a new process.
	50	The new process (child process) is an exact copy of the
	51	calling process (parent process) except for the following:
	52	.Bl -bullet -offset indent
	53	.It
	54	The child process has a unique process ID.
	55	.It
	56	The child process has a different parent
	57	process ID (i.e., the process ID of the parent process).
	58	.It
	59	The child process has its own copy of the parent's descriptors.
	60	These descriptors reference the same underlying objects, so that,
	61	for instance, file pointers in file objects are shared between
	62	the child and the parent, so that an
	63	.Xr lseek 2
	64	on a descriptor in the child process can affect a subsequent
	65	.Xr read
	66	or
	67	.Xr write
	68	by the parent.
	69	This descriptor copying is also used by the shell to
	70	establish standard input and output for newly created processes
	71	as well as to set up pipes.
	72	.It
	73	The child processes resource utilizations
	74	are set to 0; see
	75	.Xr setrlimit 2 .
	76	.El
	77	.Sh RETURN VALUES
	78	Upon successful completion,
	79	.Fn fork
	80	returns a value
	81	of 0 to the child process and returns the process ID of the child
	82	process to the parent process. Otherwise, a value of -1 is returned
	83	to the parent process, no child process is created, and the global
	84	variable
	85	.Va errno
	86	is set to indicate the error.
	87	.Sh ERRORS
	88	.Fn Fork
	89	will fail and no child process will be created if:
	90	.Bl -tag -width Er
	91	.It Bq Er EAGAIN
	92	The system-imposed limit on the total
	93	number of processes under execution would be exceeded.
	94	This limit is configuration-dependent.
	95	.It Bq Er EAGAIN
	96	The system-imposed limit
	97	.Dv MAXUPRC
	98	.Pq Aq Pa sys/param.h
	99	on the total number of
	100	processes under execution by a single user would be exceeded.
	101	.It Bq Er ENOMEM
	102	There is insufficient swap space for the new process.
	103	.El
	104	.Sh SEE ALSO
	105	.Xr execve 2 ,
	106	.Xr wait 2
	107	.Sh HISTORY
	108	A
	109	.Fn fork 2
	110	function call appeared in
	111	.At v6 .