Disabling/enabling services in Ubuntu (UPDATED)

Recent versions of Ubuntu have changed the way that system services start up.  Presumably this reflects a policy change in Linux systems.
There are now THREE different ways for Linux services to start automatically at boot...

1. New way: /etc/init/example.conf
   
   • If you find such a file, open it up in an editor and examine its startup conditions (beginning with "start on"). 
   • To prevent the service from starting, comment out the "start on" line (change "start on" to '#start on")
   Alternatively, I'm told that you can say:

   echo "manual" >/etc/init/example.conf.override

   but I haven't tried this yet. 
   
   
2. Legacy way: /etc/init.d/example and /etc/rc5.d/S20example.
   To start a service using this traditional technique...
   
   • Place a shell script in /etc/init.d/example.
   • Create a symbolic link to /etc/init.d/example for each run level you want the service to auto-start in. For example:  ln -s /etc/init.d/example /etc/rc5.d/S20example would start the example service in Run Level 5.  
   • Symbolic links named something like /etc/rcN.d/K20example provide a way to stop a service cleanly when the machine changes run level (e.g. shuts down).
   • You may recall that run level 2 is single-user text-mode; 3 is multi-user text mode; 5 is multi-user GUI mode.
   • The numbers after 'S' or 'K' provide a crude way of tweaking service start-up order, so that for example you can make sure that a database service starts up before an SQL-based application server.
   • To stop a service starting in this way, you can just delete the symlinks i.e. rm /etc/rc*.d/S*example.
     
   
   
3. Bastardized legacy way: /etc/init.d/example by itself.
• Some services still use /etc/init.d/example but rather than relying on symlinks such as /etc/rc*.d/S*example, they use a new syntax for startup conditions, placed in comments near the top of
  /etc/init.d/example.
  
  
• For example, the Mathopd web server is controlled solely from
  /etc/init.d/mathopd, which contains the text:
  
  ### BEGIN INIT INFO
  # Provides:          mathopd
  # Required-Start:    $local_fs $remote_fs $network $syslog
  # Required-Stop:     $local_fs $remote_fs $network $syslog
  # Default-Start:     2 3 4 5
  # Default-Stop:      0 1 6
  # Short-Description: Mathopd web server
  ### END INIT INFO
  
  
Just delete all of the lines (from BEGIN INIT INFO to END INIT INFO) and replace them with a single line containing the word exit and it will not restart after you reboot the box.

After rebooting, run "netstat -tan | grep LISTEN" to make sure you know what's bound to your external network interfaces (i.e. anything other than 127.0.0.1 for IPv4, or ::1 for IPv6).

If you see an IPv6 service listed like this:

     tcp6   0   0 :::51413     :::*        LISTEN 

it simply means that the service is listening on all IPv6 interfaces, on port 51413.  It's the IPv6 equivalent of showing 0.0.0.0:51413.

Further reading at http://overtag.dk/wordpress/2011/02/headaches-over-disablingenabling-services-init-d-scripts-in-ubuntu-10-10/ .   See also http://ubuntuforums.org/showthread.php?t=1519273 .