2004-11-03 13:51:07 +00:00
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified by Michael Haardt (michael@moria.de)
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.\" Modified Sat Jul 24 13:22:07 1993 by Rik Faith (faith@cs.unc.edu)
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.\" Modified 21 Aug 1994 by Michael Chastain (mec@shell.portal.com):
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.\" Referenced 'clone(2)'.
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.\" Modified 1995-06-10, 1996-04-18, 1999-11-01, 2000-12-24
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.\" by Andries Brouwer (aeb@cwi.nl)
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2004-11-03 14:43:40 +00:00
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.\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
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2004-11-03 13:51:07 +00:00
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.\" Added notes on capability requirements
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.\"
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.TH FORK 2 2004-05-27 "Linux 2.6.6" "Linux Programmer's Manual"
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.SH NAME
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fork \- create a child process
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.SH SYNOPSIS
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.B #include <sys/types.h>
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.br
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.B #include <unistd.h>
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.sp
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.B pid_t fork(void);
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.SH DESCRIPTION
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.B fork
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creates a child process that differs from the parent process only in its
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PID and PPID, and in the fact that resource utilizations are set to 0.
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File locks and pending signals are not inherited.
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.PP
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Under Linux,
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.B fork
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is implemented using copy-on-write pages, so the only penalty incurred by
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fork is the time and memory required to duplicate the parent's page tables,
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and to create a unique task structure for the child.
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.SH "RETURN VALUE"
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On success, the PID of the child process is returned in the parent's thread
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of execution, and a 0 is returned in the child's thread of execution. On
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failure, a \-1 will be returned in the parent's context, no child process
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will be created, and
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.I errno
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will be set appropriately.
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.SH ERRORS
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.TP
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.B EAGAIN
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.B fork
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cannot allocate sufficient memory to copy the parent's page tables and
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allocate a task structure for the child.
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.TP
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.B EAGAIN
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It was not possible to create a new process because the caller's
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.B RLIMIT_NPROC
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resource limit was encountered.
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To exceed this limit, the process must have either the
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.BR CAP_SYS_ADMIN
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or the
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.BR CAP_SYS_RESOURCE
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capability.
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.TP
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.B ENOMEM
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.B fork
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failed to allocate the necessary kernel structures because memory is tight.
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.SH "CONFORMING TO"
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The
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.B fork
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2005-07-18 15:05:56 +00:00
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call conforms to SVr4, SVID, POSIX, X/OPEN, 4.3BSD.
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2004-11-03 13:51:07 +00:00
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.SH "SEE ALSO"
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.BR clone (2),
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.BR execve (2),
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.BR setrlimit (2),
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.BR vfork (2),
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.BR wait (2),
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.BR capabilities (7)
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