dual-boot time issue

Colin Watson cjwatson at ubuntu.com
Tue Jun 12 13:02:09 UTC 2018

On Tue, Jun 12, 2018 at 11:45:54AM +0000, J.Witvliet at mindef.nl wrote:
> The general issue arrises when dual-booting:
> Ubuntu_18.04 uses UTC, derived from NTP
> Windows uses Local Time, derived from hwclock.
> Normally the two can co-exists together, except, when stopping Ubuntu, System-D writes its time back to the hwclock.
> No big deal for Ubuntu (as it will use ntp), but a source of irritation under Windows.
> I do know several suggestions, like:
> a)      Make Windows10 use UTC instead of local time.
> This would solve everything once and for all FOR ME, but not achievable for others.
> b)      Make Ubuntu_18.04 use local time, with: "timedatectl set-local-rtc 1 --adjust-system-clock"
> However, I'm about to switch to Kerberos for several services, so I must use a reliable source for time.

b) seems like the proper fix, if you don't want to (or can't)
reconfigure Windows.  systemd or anything else writing to the hardware
clock isn't the problem in and of itself; it just needs to make sure to
apply the correct offset, and that's what "timedatectl set-local-rtc 1"

I don't see how this is related to using a reliable source for time.
You should probably omit the --adjust-system-clock option, since you
don't need to synchronise the system clock from the hardware clock; but
once you've run that timedatectl command once, the system should be
configured to do the right thing when writing to the hardware clock from
then on.

Colin Watson                                       [cjwatson at ubuntu.com]

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