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 No more file descriptors are available for this process.

       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
       IEEE Std 1003.1-2001, <netinet/in.h>, <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                                             SOCKET(P)