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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 (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  communica-
       tions  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 communica-
       tions domain. The address families supported by the system  are  imple-
       mentation-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  inte-
       ger,  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  fam-
              ily.
       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 pro-
              tocol 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 proto-
       cols each address family supports. The documentation for specific  pro-
       tocols 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(), shut-
       down(),    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(3P)