All of a sudden, my openHAB installation on a RPi 3 stopped working. I rebooted the RPi and checked the status. I am not able to start OH2 anymore. Any idea what is going on?
Try sudo systemctl start openhab2. You need elevated permissions to start a service.
Oh man, how stupid. 
I did another reboot and, for whatsoever reason, OH2 is up and running again.