SOCKET(3P)                                          POSIX Programmer's Manual                                         SOCKET(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult 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 follow-
       ing 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 mecha-
              nism 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  proto-
       col 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    SOCKET(3P)