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.\"     @(#)socketpair.2	6.4 (Berkeley) 3/10/91

.\"

.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>

.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>

.\" Modified 2002-07-22 by Michael Kerrisk <mtk.manpages@gmail.com>

.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>

.\" 2008-10-11, mtk: Add description of SOCK_NONBLOCK and SOCK_CLOEXEC

.\"

.TH SOCKETPAIR 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

socketpair \- create a pair of connected sockets

.SH SYNOPSIS

.BR "#include <sys/types.h>" "          /* See NOTES */"

.br

.B #include <sys/socket.h>

.PP

.BI "int socketpair(int " domain ", int " type ", int " protocol \

", int " sv [2]);

.SH DESCRIPTION

The

.BR socketpair ()

call creates an unnamed pair of connected sockets in the specified

.IR domain ,

of the specified

.IR type ,

and using the optionally specified

.IR protocol .

For further details of these arguments, see

.BR socket (2).

.PP

The file descriptors used in referencing the new sockets are returned in

.IR sv [0]

and

.IR sv [1].

The two sockets are indistinguishable.

.SH RETURN VALUE

On success, zero is returned.

On error, \-1 is returned, and

.I errno

is set appropriately.

.PP

On Linux (and other systems),

.BR socketpair ()

does not modify

.I sv

on failure.

A requirement standardizing this behavior was added in POSIX.1-2016.

.\" http://austingroupbugs.net/view.php?id=483

.SH ERRORS

.TP

.B EAFNOSUPPORT

The specified address family is not supported on this machine.

.TP

.B EFAULT

The address

.I sv

does not specify a valid part of the process address space.

.TP

.B EMFILE

The per-process limit on the number of open file descriptors has been reached.

.TP

.B ENFILE

The system-wide limit on the total number of open files has been reached.

.TP

.B EOPNOTSUPP

The specified protocol does not support creation of socket pairs.

.TP

.B EPROTONOSUPPORT

The specified protocol is not supported on this machine.

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008, 4.4BSD.

.BR socketpair ()

first appeared in 4.2BSD.

It is generally portable to/from

non-BSD systems supporting clones of the BSD socket layer (including

System\ V variants).

.SH NOTES

On Linux, the only supported domain for this call is

.B AF_UNIX

(or synonymously,

.BR AF_LOCAL ).

(Most implementations have the same restriction.)

.PP

Since Linux 2.6.27,

.BR socketpair ()

supports the

.BR SOCK_NONBLOCK

and

.BR SOCK_CLOEXEC

flags in the

.I type

argument, as described in

.BR socket (2).

.PP

POSIX.1 does not require the inclusion of

.IR <sys/types.h> ,

and this header file is not required on Linux.

However, some historical (BSD) implementations required this header

file, and portable applications are probably wise to include it.

.SH SEE ALSO

.BR pipe (2),

.BR read (2),

.BR socket (2),

.BR write (2),

.BR socket (7),

.BR unix (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.