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LISTEN(P)			    POSIX Programmer's Manual				LISTEN(P)

       listen - listen for socket connections and limit the queue of incoming connections

       #include <sys/socket.h>

       int listen(int socket, int backlog);

       The  listen()  function shall mark a connection-mode socket, specified by the socket argu-
       ment, as accepting connections.

       The backlog argument provides a hint to the implementation which the implementation  shall
       use to limit the number of outstanding connections in the socket's listen queue. Implemen-
       tations may impose a limit on backlog and silently reduce the specified value. Normally, a
       larger  backlog	argument  value  shall	result	in a larger or equal length of the listen
       queue.  Implementations shall support values  of  backlog  up  to  SOMAXCONN,  defined  in

       The  implementation  may include incomplete connections in its listen queue. The limits on
       the number of incomplete connections and completed connections queued may be different.

       The implementation may have an upper limit on the length of the listen queue-either global
       or  per accepting socket. If backlog exceeds this limit, the length of the listen queue is
       set to the limit.

       If listen() is called with a backlog argument value that is  less  than	0,  the  function
       behaves as if it had been called with a backlog argument value of 0.

       A  backlog  argument  of  0  may allow the socket to accept connections, in which case the
       length of the listen queue may be set to an implementation-defined minimum value.

       The socket in use may require the process to have appropriate privileges to use	the  lis-
       ten() function.

       Upon  successful completions, listen() shall return 0; otherwise, -1 shall be returned and
       errno set to indicate the error.

       The listen() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.


	      The socket is not bound to a local address, and the protocol does not support  lis-
	      tening on an unbound socket.

       EINVAL The socket is already connected.

	      The socket argument does not refer to a socket.

	      The socket protocol does not support listen().

       The listen() function may fail if:

       EACCES The calling process does not have the appropriate privileges.

       EINVAL The socket has been shut down.

	      Insufficient resources are available in the system to complete the call.

       The following sections are informative.





       accept()  ,  connect()  ,  socket() , the Base Definitions volume of IEEE Std 1003.1-2001,

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					LISTEN(P)
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