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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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