title: How do I register for systemd service lifecycle events?
body: <p>I want to be informed about all state changes of service units. I know there is the DBUS API which gives me signals for UnitNew and UnitRemoved, but the semantic is still unclear to me. Also the signals doesn't provide the informations I need.</p>
  
  <p>I'm using go and tried the <a href="https://github.com/coreos/go-systemd" rel="nofollow noreferrer">go-systemd lib</a> from coreos. They provide a way to "subscribe" but it's in fact polling all the unit information available in the system. I do not want to do so every few milliseconds, just to get informed about statechanges.</p>
  
  <p>I also tried the default org.freedesktop.DBus.Properties but I can not get this working.</p>
  
  <p>Please help If you can, I'm out of ideas.</p>