Re: [chrony-users] Does Chronyd update the hardware clock?

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On Tue, 10 Jun 2014, Joe M wrote:

Hello Bill,

Thank you for your quick and detailed reply.

I am trying to figure out if Chronyd updates the hardware clock.

It can (writertc is the command in chronyc) but in general it does not. It
measures the time and rate of the hardware clock in order to better use it to
set the time next time the computer is switched on. Mind you, the rate is
deternined while the computer is hot, while the error due to the rate not
being equal to 1 sec/sec  occurs while the computer is off and cold, and thus
the rate difference then is different from when it is hot. But the process is
better than nothing.

I presume that the functionality described above has to do with
setting the "rtcfile" in chrony.conf. Instead of setting "rtcfile" if
"rtcsync" is used, then does chrony automatically update the hardware

According to the docs, rtcsync enables the "11 min mode" of the kernel, where
every 11 min the system time is copied over to the rtc. This does NOT allow
one to calibrate the rtc-- eg determining its drift to compensate for that
drift when next chronyd is started. Note that hwclock can also calibrate the drift but again not if the chrony
foools around with the rtc.

If you told us what you hope to accomplish, we might be able to give better

I tested this by changing my system clock and hwclock to -2 mins. With
"rtcsync" and starting the chronyd process, it set the system clock
and the hwclock to the correct time. I just want to confirm that it is
expected behaviour.

The rest of you explanation makes perfect sense, Thanks for the
detailed explanation.

Thanks again,

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