How should I choose a port number for my server?

  The list of registered port assignments can be found in STD 2 or RFC
  1700.  Choose one that isn't already registered, and isn't in
  /etc/services on your system.  It is also a good idea to let users
  customize the port number in case of conflicts with other un-
  registered port numbers in other servers.  The best way of doing this
  is hardcoding a service name, and using getservbyname() to lookup the
  actual port number.  This method allows users to change the port your
  server binds to by simply editing the /etc/services file.