Q. systemd: restart down service
A. A big benefit of systemd over traditional service launchers is its ability
to monitor services and optionally restart them if they stop unexpectedly.
In the past I would write little scripts to ensure important services were running.
Now you can simply use Restart=always in the service's unit file.
This will restart the service if crashes.
For example, for dnsmasq:
Description=DNS caching server.
Restart=always <!--- KEY LINE
There are other choices for the Restart option