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 listen(2)							   listen(2)




 NAME
      listen - listen for connections on a socket

 SYNOPSIS
      #include <&lt&lt&lt;sys/socket.h>&gt&gt&gt;

      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.	Except for AF_VME_LINK, 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
      and AF_VME_LINK, 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
      <&lt&lt&lt;sys/socket.h>&gt&gt&gt;.  SOMAXCONN is currently set to 4096.  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 11i: November 2000






 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)).

 FUTURE DIRECTION
      Currently, the default behavior is the HP-UX BSD Sockets; however, it
      might be changed to X/Open Sockets in a future release.  At that time,
      any HP-UX BSD Sockets behavior that is incompatible with X/Open
      Sockets might be obsoleted.  Applications that conform to the X/Open
      specification now will avoid migration problems (see
      xopen_networking(7)).

 MULTITHREAD USAGE
      The listen() system call is thread-safe.	It has a cancellation point;
      and it is async-cancel safe, async-signal safe, and fork-safe.

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

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

 STANDARDS CONFORMANCE
      listen(): XPG4


























 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000