Comment 7 for bug 837954

I can't start it manually anyway until I run `systemctl stop knockd.service`. `systemctl start knockd.service` will start it after it's stopped and finally `ps` will show it:
root 2885 2.5 0.0 8748 3584 ? Ss 22:04 0:00 /usr/sbin/knockd -d -i wlan0