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 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. 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 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  argu-
       ment 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  implementa-
       tion-defined minimum value.

       The  socket  in  use may require the process to have appropriate privi-
       leges 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.
       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 original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .