OK, on the “old” Linux machines you mentioned above, start by “manually” deploying the agent script (and nothing more) as described her (deep link):
Proceed here by accessing it via SSH (deep link):
Then check the connections and add the host to the monitoring. The script already checks many common services.
You need more services, then add Checkmk plugins as described here (deep link):
Or add Nagios plugins as described here (deep link):