Using my retropie-Kodi combo for a while now I walked into some issues where Kodi wasn’t active for some reason (usually me forgetting about it after rebooting my Pi). This interfered with my SickRage Kodi notification.
With the release of Retropie 4.0 this option has finally been built-in! After upgrading to the new Retropie release you can go to the retropie-setup menu and choose the following options:
C Configuration / tools > 001 autostart – Auto-start Emulation Station / Kodi on boot > 2 Start Kodi at boot (exit for Emulation Station)
Exit the retropie setup and restart your raspberry. You will now be greeted by your Kodi! On exiting Kodi you will go back to emulation station.