Knowing what a restart does before you do it.
RELOAD VERSUS RESTART
Reload re-reads configuration without dropping existing connections, where supported. Prefer it on a live site.
Restart stops and starts, dropping connections. Necessary for some changes.
TEST FIRST
Web servers and most major services offer a configuration test command. Run it before reloading or restarting.
A restart with broken configuration means the service does not come back, and the site is down until you find the error.
THE ORDER OF DEPENDENCIES
Some services depend on others. Restarting a database while applications are connected causes errors in those applications, which may need their own restart afterwards.
WHEN A SERVICE WILL NOT START
Check systemctl status, which usually names the problem Check the service's error log Check whether another process is holding the port Check whether a configuration file has a syntax error
WHAT NOT TO DO
Restarting repeatedly in the hope that it works. Read the error instead.
REBOOTING
Necessary after kernel updates. Schedule it, and confirm all services come back afterwards.
