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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

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 argument, as accepting con-
       nections.

       The backlog argument provides a hint to the implementation which the implementation shall use to limit the num-
       ber  of outstanding connections in the socket's listen queue. Implementations 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  incom-
       plete 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 listen() 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 listening 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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                           LISTEN(3P)