Shorter, simpler, non-legacy answer:
journalctl -u [unitfile] Where [unitfile] is the systemd .service name. Eg, to see messages from docker.service,
journalctl --unit=docker Shorter, simpler, non-legacy answer:
journalctl -u [unitfile] Where [unitfile] is the systemd .service name. Eg, to see messages from docker.service,
journalctl --unit=docker