Keeping clocks correct.
WHY IT MATTERS
Logs from different machines cannot be correlated if clocks disagree Certificates fail validation with a wrong clock Scheduled tasks run at the wrong time Authentication tokens depending on time stop working
HOW TO SEE THE CURRENT SETTING
The date command, or timedatectl.
WHAT TO SET SERVERS TO
A single standard, universally, with local time applied at presentation.
WHY
It removes ambiguity and avoids daylight saving problems entirely.
WHAT SYNCHRONISATION SERVICES DO
Keep the clock aligned with reference sources.
WHAT TO CHECK
That synchronisation is enabled and actually working.
WHY THAT SECOND PART
The service can be running while failing to reach any source.
WHAT A DRIFTING CLOCK CAUSES
Intermittent, inexplicable failures that resist diagnosis.
WHAT TO DO ABOUT APPLICATION TIME ZONES
Set them in the application, not by changing the server.
WHY
Other applications on the same machine depend on the server setting.
WHAT TO BE CAREFUL WITH
Changing the clock abruptly on a running database.
WHAT TO PREFER
Gradual correction, which synchronisation services do by default.
WHAT TO VERIFY AFTER ANY CHANGE
Scheduled tasks, whose times shift with the zone.
