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SubjectRe: PROBLEM: Linux updates RTC secretly when clock synchronizes
Hi!

> >> The offset needs to be sufficient to handle the case of the RTC
> >> being set to local time and the boot and first ntp sync occurring on
> >> opposite sides of a Daylight Savings Time change. A couple of
> >> timezones use a DST offset of 90 minutes, so if it's less than that,
> >> there will be problems.
>
> > There is a related problem, where if you are running something which
> > can suspend, like a laptop, but not using integrated apm to do it
> > (for instance a laptop which has a broken BIOS), then suspending
> > 'freezes' the system time, which is wrong on resume (as the power
> > management event appears to be invisible to Linux). Then this goes
> > and blats over the (correct) RTC time. If you then get a network
> > connection up, ntp won't adjust the time as it's too far out.
>
> That sounds like a configuration error to me, and here's why.
>
> 1. One of the available reference clocks for xntpd is the local
> RTC, type 1 in the list of reference clock types, and that
> should ALWAYS be listed as one of the reference clocks to use,
> but with a higher stratum than any other reference clock used.
>
> 2. My experience with the xntpd driver suggests that if no better
> reference is available and the RTC is one of the listed clocks,
> then it ALWAYS adjusts the time to match the RTC, irrespective
> of the time difference between them.

This sounds racy. What if kernel is faster and destroys RTC just after
resume and before xntpd ca run?
Pavel
--
Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.

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