Re: [chrony-users] RTC trim and offset reduced to 1ms

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On Thu, Jan 16, 2020 at 10:11:02AM +0000, Seoli Luca (M) wrote:
> Hi all,
> I'm trying to configure chronyd to set RTC time considering System time and its variations. In particular, I'd like to get an offset between RTC time and Sys time less than 1ms (milliseconds). Is it possibile?
> Below my configuration file and some statistics I found in my rtc.log file.

No, chronyd can set the RTC only with about 0.5 second accuracy due to
the 1s resolution of the RTC (it doesn't try to time the operation
unlike the kernel or hwclock). As long as the estimated offset is
smaller than 1 second, chronyd will not try to trim the RTC, even if
the rtcautotrim threshold is smaller.

I'd suggest to disable the RTC tracking in chrony and run hwclock
every few minutes (e.g. from cron).

> ---- Configuration File ----
> hwclockfile /etc/adjtime
> rtcautotrim 0.001
> rtcdevice /dev/rtc
> rtcfile /var/lib/chrony/rtc
> logdir /var/log/chrony
> log rtc statistics measurements tracking
> dumponexit

Miroslav Lichvar

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