SOCKETPAIR(2)

NAME
socketpair - create a pair of connected sockets

SYNOPSIS
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>

int socketpair(int domain, int type, int protocol, int sv[2]);

DESCRIPTION
The socketpair() call creates an unnamed pair of connected sockets in the specified domain, of the specified type, and using the optionally specified protocol. For further details of these arguments, see socket(2).

The file descriptors used in referencing the new sockets are returned in sv[0] and sv[1]. The two sockets are indistinguishable.

RETURN VALUE
On success, zero is returned. On error, -1 is returned, errno is set appropriately, and sv is left unchanged

On Linux (and other systems), socketpair() does not modify sv on failure. A requirement standardizing this behavior was added in POSIX.1-2016.

ERRORS

EAFNOSUPPORT
    The specified address family is not supported on this machine.

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

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

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

EOPNOTSUPP
    The specified protocol does not support creation of socket pairs.

EPROTONOSUPPORT
    The specified protocol is not supported on this machine.

CONFORMING TO
POSIX.1-2001, POSIX.1-2008, 4.4BSD. 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).

NOTES
On Linux, the only supported domains for this call are AF_UNIX (or synonymously, AF_LOCAL) and AF_TIPC (since Linux 4.12).

Since Linux 2.6.27, socketpair() supports the SOCK_NONBLOCK and SOCK_CLOEXEC flags in the type argument, as described in socket(2).

POSIX.1 does not require the inclusion of <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.

SEE ALSO
pipe(2), read(2), socket(2), write(2), socket(7), unix(7)

COLOPHON
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