listen(2)                                                         listen(2)




 NAME
      listen - listen for connections on a socket

 SYNOPSIS
      #include <sys/socket.h>

      int listen(int s, int backlog);

 DESCRIPTION
      To accept connections, a socket is first created using socket(), a
      queue for incoming connections is activated using listen(), and then
      connections are accepted using accept().  listen() applies only to
      unconnected sockets of type SOCK_STREAM.  If the socket has not been
      bound to a local port before listen() is invoked, the system
      automatically binds a local port for the socket to listen on (see
      inet(7F)).  For sockets in the address family AF_CCITT, the socket
      must be bound to an address by using bind() before connection
      establishment can continue, otherwise an EADDREQUIRED error is
      returned.

      A listen queue is established for the socket specified by the s
      parameter, which is a socket descriptor.

      backlog defines the desirable queue length for pending connections.
      The actual queue length may be greater than the specified backlog . If
      a connection request arrives when the queue is full, the client will
      receive an ETIMEDOUT error.

      backlog is limited to the range of 0 to SOMAXCONN, which is defined in
      <sys/socket.h>.  SOMAXCONN is currently set to 20.  If any other value
      is specified, the system automatically assigns the closest value
      within the range.  A backlog of 0 specifies only 1 pending connection
      is allowed at any given time.

 DEPENDENCIES
    AF_CCITT:
      Call-acceptance can be controlled by the X25_CALL_ACPT_APPROVAL
      ioctl() call described in RETURN VALUE .  Upon successful completion,
      listen() returns 0; otherwise, it returns -1 and sets errno to
      indicate the error.

 ERRORS
      listen() fails if any of the following conditions are encountered:

           [EBADF]             s is not a valid file descriptor.

           [EDESTADDRREQ]      The socket s has not been bound to an address
                               by using bind() .

           [ENOTSOCK]          s is a valid file descriptor but it is not a
                               socket.



 Hewlett-Packard Company            - 1 -    HP-UX Release 10.20:  July 1996






 listen(2)                                                         listen(2)




           [EOPNOTSUPP]        The socket referenced by s does not support
                               listen() .

           [EINVAL]            The socket has been shut down or is already
                               connected (see socketx25(7)).

 AUTHOR
      listen() was developed by the University of California, Berkeley.

 FUTURE DIRECTION
      The default behavior in this release is still the classic HP-UX BSD
      Sockets, however it will be changed to X/Open Sockets in some future
      release.  At that time, any HP-UX BSD Sockets behavior which is
      incompatible with X/Open Sockets may be obsoleted.  HP customers are
      advised to migrate their applications to conform to X/Open
      specification( see xopen_networking(7) ).

 SEE ALSO
      accept(2), connect(2), socket(2), socketx25(7), af_ccitt(7F),
      inet(7F), xopen_networking(7).

 STANDARDS CONFORMANCE
      listen(): XPG4































 Hewlett-Packard Company            - 2 -    HP-UX Release 10.20:  July 1996