man2/socketpair.2

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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 2020-06-09 "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,
.I errno
is set appropriately, and
.I sv
is left unchanged
.PP
On Linux (and other systems),
.BR socketpair ()
does not modify
.I sv
on failure.
A requirement standardizing this behavior was added in POSIX.1-2008 TC2.
.\" 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 domains for this call are
.B AF_UNIX
(or synonymously,
.BR AF_LOCAL )
and
.B AF_TIPC
.\" commit: 70b03759e9ecfae400605fa34f3d7154cccbbba3
(since Linux 4.12).
.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)