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  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 .