dual-boot time issue

J.Witvliet at mindef.nl J.Witvliet at mindef.nl
Tue Jun 12 13:34:29 UTC 2018

-----Original Message-----
From: ubuntu-users [mailto:ubuntu-users-bounces at lists.ubuntu.com] On Behalf Of Colin Watson
Sent: dinsdag 12 juni 2018 15:02
To: ubuntu-users at lists.ubuntu.com
Subject: Re: dual-boot time issue

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.

Option a) should be better, but is beyond my reach (especially for other systems)
Option B) seems nice, but when using Kerberos, you need a steady and reliable time source.

For Ubuntu there is no problem, it works well with our own time-source,
But the problem arises when people shuts down and subsequently boots windows (yeah, I know, bad move altogether, but such is life)
So during shutdown I think the system should either:
- Not write to the hwclock at all, or,
- write the converted UTC-2-LTC (to keep the win-users happy)

Up to now, I failed to see a system option to influence this behavior.
(could I mislead the system by using the package: "fake-hwclock", or would I break other parts?)

HtH, Hans

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