From Linux Man Pages
socketpair - create a pair of connected sockets
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int socketpair(int d, int type, int protocol, int sv[2]);
DESCRIPTION
The socketpair() call creates an unnamed pair of connected sockets in the specified domain d, of the specified
type, and using the optionally specified protocol. The 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, and errno is set appropriately.
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 Too many descriptors are in use by this process.
ENFILE The system 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
4.4BSD, POSIX.1-2001. The socketpair() function call 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 domain for this call is AF_UNIX (or synonymously, AF_LOCAL). (Most implementations
have the same restriction.)
RELATED
pipe(2), read(2), socket(2), write(2), unix(7)
CATEGORY