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



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

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  descrip-
       tors used in referencing the created sockets shall be returned in socket_vector[0] and socket_vector[1].

       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  fol-
       lowing 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 mecha-
              nism 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  proto-
       col 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.

ERRORS
       The socketpair() function shall fail if:

       EAFNOSUPPORT

              The implementation does not support the specified address family.

       EMFILE No more file descriptors are available for this process.

       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
       socket(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                SOCKETPAIR(3P)