LISTEN(P)                                                                               LISTEN(P)



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

SYNOPSIS
       #include <sys/socket.h>

       int listen(int socket, int backlog);


DESCRIPTION
       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
       <sys/socket.h>.

       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.

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

ERRORS
       The listen() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

       EDESTADDRREQ

              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.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EOPNOTSUPP
              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.

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


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       accept()  ,  connect()  ,  socket() , the Base Definitions volume of IEEE Std 1003.1-2001,
       <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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .



POSIX                                          2003                                     LISTEN(P)