SOCKETPAIR(3)              POSIX Programmer's Manual             SOCKETPAIR(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       socketpair -- create a pair of connected sockets

SYNOPSIS
       #include <sys/socket.h>

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

DESCRIPTION
       The socketpair() function shall create an unbound pair of connected
       sockets in a specified domain, of a specified type, under the protocol
       optionally specified by the protocol argument. The two sockets shall be
       identical. The file descriptors used in referencing the created sockets
       shall be returned in socket__vector[0] and socket__vector[1].  The file
       descriptors shall be allocated as described in Section 2.14, File
       Descriptor Allocation.

       The socketpair() function takes the following arguments:

       domain      Specifies the communications domain in which the sockets
                   are to be created.

       type        Specifies the type of sockets to be created.

       protocol    Specifies a particular protocol to be used with the
                   sockets.  Specifying a protocol of 0 causes socketpair() to
                   use an unspecified default protocol appropriate for the
                   requested socket type.

       socket__vector
                   Specifies a 2-integer array to hold the file descriptors of
                   the created socket pair.

       The type argument specifies the socket type, which determines the
       semantics of communications over the socket. The following socket types
       are defined; implementations may specify additional socket types:

       SOCK_STREAM   Provides sequenced, reliable, bidirectional, connection-
                     mode byte streams, and may provide a transmission
                     mechanism for out-of-band data.

       SOCK_DGRAM    Provides datagrams, which are connectionless-mode,
                     unreliable messages of fixed maximum length.

       SOCK_SEQPACKET
                     Provides sequenced, reliable, bidirectional, connection-
                     mode transmission paths for records. A record can be sent
                     using one or more output operations and received using
                     one or more input operations, but a single operation
                     never transfers part of more than one record. Record
                     boundaries are visible to the receiver via the MSG_EOR
                     flag.

       If the protocol argument is non-zero, it shall specify a protocol that
       is supported by the address family. If the protocol argument is zero,
       the default protocol for this address family and type shall be used.
       The protocols supported by the system are implementation-defined.

       The process may need to have appropriate privileges to use the
       socketpair() function or to create some sockets.

RETURN VALUE
       Upon successful completion, this function shall return 0; otherwise, -1
       shall be returned and errno set to indicate the error, no file
       descriptors shall be allocated, and the contents of socket__vector shall
       be left unmodified.

ERRORS
       The socketpair() function shall fail if:

       EAFNOSUPPORT
              The implementation does not support the specified address
              family.

       EMFILE All, or all but one, of the file descriptors available to the
              process are currently open.

       ENFILE No more file descriptors are available for the system.

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

       EPROTONOSUPPORT
              The protocol is not supported by the address family, or the
              protocol is not supported by the implementation.

       EPROTOTYPE
              The socket type is not supported by the protocol.

       The socketpair() function may fail if:

       EACCES The process does not have appropriate privileges.

       ENOBUFS
              Insufficient resources were available in the system to perform
              the operation.

       ENOMEM Insufficient memory was available to fulfill the request.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The documentation for specific address families specifies which
       protocols each address family supports. The documentation for specific
       protocols specifies which socket types each protocol supports.

       The socketpair() function is used primarily with UNIX domain sockets
       and need not be supported for other domains.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.14, File Descriptor Allocation, socket()

       The Base Definitions volume of POSIX.1-2017, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                        SOCKETPAIR(3)
