Hi Miroslav,
thank you for your quick reply!
I've done some further experiments and I'm pretty sure now that this task cannot be handled by chrony alone due to the different drift if running/stopped.On Mon, Oct 15, 2018 at 10:10:38AM +0200, Leo von Klenze wrote:Hello, I've a cubietruck with a very weird RTC. It is off by about 2384 seconds per day if the box is not running. While running the offset is just about 480s per day.That's bad. Unless the board is always running, so the drift doesn't change so much, I'm not sure how much the RTC support in chrony will be useful.
No, there are no errors. Chrony states the drift in rtcdata as long as the RTC is not synchronized with the SysClock. Afterwards rtcdata reports no drift anymore.Is there anything chrony can do about it? I'm not quite sure out of the docs what chrony exactly is doing with the drift f the RTC. I'm using rtcfile option in config and "-s" switch on startup. However chrony sets the system clock from the RTC on startup but without any correction (as far as I can see).AFAIK there is no limit on the frequency error. Are there any errors from chronyd in the system log? What does the rtc file contain when chronyd is starting? What does "chronyc rtcdata" print?
Can chrony handle such a case or do I have go get hwclock with /etc/adjtime in place as well?It depends on what are your expectations. It certainly won't be able to compensate for the "off" drift. You can try hwclock, but I doubt it would do better (assuming chrony works as expected).
I've implemented the following scenario now and it seems to work well enough:
- I've calculated once the drift when box is powered off and written it to /etc/adjtime
1) on boot I set the Sysclock from the RTC via hwclock. hwclocks
uses the drift from /etc/adjtime
2) afterwards chrony is started and I configured chrony to
synchronize the RTC on runtime
3) on shutdown I ensure that the RTC is set to the Sysclock one
last time via hwclock
So hwclock manages the drift during power off, chrony during running. It seems to qork quite well.
As far as I've understood now, it is just hard for chrony to
manage both drifts since they are that different.
Leo von
Klenze
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