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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 (consult 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 descriptors 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 unspec-
              ified  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  socket-
       pair() 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  fam-
              ily.
       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 pro-
              tocol 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 proto-
       cols each address family supports. The documentation for specific  pro-
       tocols 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, Copyright (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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                       SOCKETPAIR(3P)