Linux/Systemd - Not installed service returns 'inactive' instead

[bt]

I noticed that in https://github.com/kardianos/service/blob/master/service_systemd_linux.go#L218 when checking for Status() of a service that's not installed, it returns inactive instead.

I'm running this on Ubuntu server and here is example output:

$ systemctl is-active asd
inactive
$ systemctl is-active asfdsafdsad
inactive

Both asd and asfdsafdsad are not valid services, so they shouldn't be returning inactive. Therefore it's not possible to check whether a service is installed or not -- ie. it's not possible to get ErrNotInstalled.

I'm not sure if there's a workaround at this time but I'll investigate. Potentially we might have to fallback to checking whether such file exists in /etc/systemd/system if the response from systemd is inactive?