pipe.2: Note that 'pipefd' is left unchanged in the event of an error

[thirdparty/man-pages.git] / man2 / vfork.2

.\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl), 1 Nov 1999
.\" and Copyright 2006, 2012, 2017 Michael Kerrisk <mtk.manpages@gmail.com>
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.\" 1999-11-10: Merged text taken from the page contributed by
.\" Reed H. Petty (rhp@draper.net)
.\"
.TH VFORK 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
vfork \- create a child process and block parent
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.PP
.B pid_t vfork(void);
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.BR vfork ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.12:
.nf
(_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.TP 4
.fi
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.\"     || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.PD
.RE
.ad b
.SH DESCRIPTION
.SS Standard description
(From POSIX.1)
The
.BR vfork ()
function has the same effect as
.BR fork (2),
except that the behavior is undefined if the process created by
.BR vfork ()
either modifies any data other than a variable of type
.I pid_t
used to store the return value from
.BR vfork (),
or returns from the function in which
.BR vfork ()
was called, or calls any other function before successfully calling
.BR _exit (2)
or one of the
.BR exec (3)
family of functions.
.SS Linux description
.BR vfork (),
just like
.BR fork (2),
creates a child process of the calling process.
For details and return value and errors, see
.BR fork (2).
.PP
.BR vfork ()
is a special case of
.BR clone (2).
It is used to create new processes without copying the page tables of
the parent process.
It may be useful in performance-sensitive applications