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 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

       accept(), bind(), connect(), getsockname(), getsockopt(),  listen(),  recv(),  recvfrom(),
       recvmsg(), send(), sendmsg(), setsockopt(), shutdown(), socketpair()

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