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Comments on How to reset time in Ubuntu after replacing CMOS battery?

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How to reset time in Ubuntu after replacing CMOS battery?

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How to reset time in Ubuntu after replacing CMOS battery?

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posted 3 months ago

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By default modern Ubuntu versions run the service systemd-timesyncd in the background. It fetches the time at regular intervals and should automatically set your system time when an NTP server is reachable.

Setting the time in Ubuntu manually

Since Ubuntu use systemd, the normal systemd procedure with timedatectl is used.

From man timedatectl:

set-time [TIME]
Set the system clock to the specified time. This will also update the RTC time accordingly. The time may be specified in the format "2012-10-30 18:17:16".

So, to set the time manually just run the command:

sudo timedatectl set-time "2025-01-07 18:17:16"

Setting the time automatically

I cant't find a concrete command to trigger an NTP sync, but restarting the systemd-timesyncd service should do the trick if you don't want to wait for the automatic sync.

sudo systemctl restart systemd-timesyncd

posted 3 months ago

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Note that some NTP tools will only jump time less than 15 minutes. The manpage should tell you what `... (1 comment)

polydact‭ wrote 4 days ago

Note that some NTP tools will only jump time less than 15 minutes. The manpage should tell you what systemd-timesyncd (sorry I did not look for you), but usually an explicit request to sync will cause a jump.

The purpose of not automatically jumping time more than 15 minutes is when something is already horribly wrong, e.g. bad timezone, jumping time can make it worse or cause other problems.

Also when time is quite close but not exact, NTP tools may choose to "slew" time by changing the effective local clock speed a little to get the system correct in a few hours. This is less invasive for small changes.