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 listen(2)                                                         listen(2)

 NAME    [Toc]    [Back]
      listen - listen for connections on a socket

 SYNOPSIS    [Toc]    [Back]
      #include <sys/socket.h>

      int listen(int s, int backlog);

 DESCRIPTION    [Toc]    [Back]
      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
      <sys/socket.h>.  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    [Toc]    [Back]
      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    [Toc]    [Back]
      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

 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003

 listen(2)                                                         listen(2)

           [EOPNOTSUPP]        The socket referenced by s does not support

           [EINVAL]            The socket has been shut down or is already

 FUTURE DIRECTION    [Toc]    [Back]
      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

 AUTHOR    [Toc]    [Back]
      listen() was developed by HP and the University of California,

 SEE ALSO    [Toc]    [Back]
      accept(2), connect(2), socket(2), thread_safety(5),
      xopen_networking(7), inet(7F).

      listen(): XPG4

 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003
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