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 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.

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

       socket()

       The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .