[Service] # empty exec prevents error "docker.service has more than one ExecStart= setting, which is only allowed for Type=oneshot services. Refusing." ExecStart= ExecStart=/usr/bin/dockerd -H fd:// --log-driver=syslog
This enables syslog logging for the docker daemon. The file should be created in the appropriate directory with owner root, which typically would be
/etc/systemd/system/docker.service.d on e.g. Ubuntu 16.04.