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

       socket — create an endpoint for communication

SYNOPSIS

       #include <sys/socket.h>

       int socket(int domain, int type, int protocol);

DESCRIPTION

       The  socket()  function  shall  create  an  unbound  socket in a communications domain, and return a file
       descriptor that can be used in later function calls that operate on sockets. The file descriptor shall be
       allocated as described in Section 2.14, File Descriptor Allocation.

       The socket() function takes the following arguments:

       domain      Specifies the communications domain in which a socket is to be created.

       type        Specifies the type of socket to be created.

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

       The domain argument specifies the address family used in the communications domain. The address  families
       supported by the system are implementation-defined.

       Symbolic constants that can be used for the domain argument are defined in the <sys/socket.h> header.

       The  type  argument  specifies  the socket type, which determines the semantics of communication 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()  function  or  to  create  some
       sockets.

RETURN VALUE

       Upon  successful  completion,  socket()  shall return a non-negative integer, the socket file descriptor.
       Otherwise, a value of -1 shall be returned and errno set to indicate the error.

ERRORS

       The socket() function shall fail if:

       EAFNOSUPPORT
              The implementation does not support the specified address family.

       EMFILE All file descriptors available to the process are currently open.

       ENFILE No more file descriptors are available for the system.

       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 socket() 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 application can determine whether an address family is supported by trying to create  a  socket  with
       domain set to the protocol in question.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section  2.14,  File  Descriptor  Allocation,  accept(),  bind(), connect(), getsockname(), getsockopt(),
       listen(), recv(), recvfrom(), recvmsg(), send(), sendmsg(), setsockopt(), shutdown(), socketpair()

       The Base Definitions volume of POSIX.1‐2017, <netinet_in.h>, <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                                        SOCKET(3POSIX)