Man

Command Section
SOCKETPAIR(2)             FreeBSD System Calls Manual            SOCKETPAIR(2)

NAME
     socketpair - create a pair of connected sockets

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>

     int
     socketpair(int domain, int type, int protocol, int *sv);

DESCRIPTION
     The socketpair() system call creates an unnamed pair of connected sockets
     in the specified communications domain, 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.

     The SOCK_CLOEXEC and SOCK_NONBLOCK flags in the type argument apply to
     both descriptors.

RETURN VALUES
     The socketpair() function returns the value 0 if successful; otherwise
     the value -1 is returned and the global variable errno is set to indicate
     the error.

ERRORS
     The call succeeds unless:

     [EMFILE]           Too many descriptors are in use by this process.

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

     [EPROTONOSUPPORT]  The specified protocol is not supported on this
                        machine.

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

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

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

HISTORY
     The socketpair() system call appeared in 4.2BSD.

BUGS
     This call is currently implemented only for the UNIX domain.

FreeBSD 11.1-RELEASE-p4           May 4, 2015          FreeBSD 11.1-RELEASE-p4
Command Section