Abraham Varricatt

Note To Self


Synchronizing time on a dual-boot system

posted on

The time displayed by my OS is different between Ubuntu and Windows 10. Opening the settings screen on Windows on each bootup, turning the time sync off/on was getting tiring. Here is how I solved the problem in a more permanent manner.

The root cause of the issue is due to difference in behaviour with how each OS was treating the time reported by BIOS. Ubuntu treated it as UTC time, but Windows treated it as localtime. This meant that when either of the operating systems would sync time against an online time server, it would set the BIOS clock in a manner different than the other expected.

Between the two approaches - use BIOS time as either UTC or local, I would personally prefer UTC. This would mean that BIOS would not need to be updated each time daylight savings came round every year, or if I was travelling and switched time-zones.

Unfortunately, Windows does not make it easy to use the BIOS clock as UTC time. Technically it’s possible, but it involves messing around with the Registry Editor and I’m worried that other applications wouldn’t play well with the changes.

Which leaves modifying Ubuntu as the other option. Fortunately, this isn’t too difficult. Just run the following command,

$ timedatectl set-local-rtc 1

What the above does, is tell Ubuntu to treat the BIOS clock as localtime. Restarting my system a few times and switching between the OS’s confirms that it works.