Recently discovered while making a monitoring script that systemd exposes a few properties that can be used to alert on a service that is continuously failing to start if it's set to restart indefinitely.

    # Get the number of restarts for a service to see if it exceeds an arbitrary threshold.
    systemctl show -p NRestarts "${SYSTEMD_UNIT}" | cut -d= -f2

    # Get when the service started, to work out how long it's been running, as the restart counter isn't reset once the service does start successfully.
    systemctl show -p ActiveEnterTimestamp "${SYSTEMD_UNIT}" | cut -d= -f2

    # Clear the restart counter if the service has been running for long enough based on the timestamp above
    systemctl reset-failed "${SYSTEMD_UNIT}"