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 .