On Monday, 11 September 2017 15:14:43 BST Ralph Corderoy wrote:
> More than one thing, I expect. It's possible your system is trying to
> adjust the RTC based on the divergence it notices between boot-up and
> shutdown. /etc/adjtime can be a sign of that, or
> /etc/init.d/hwclock.sh. Then ntpd might be triggering something similar
> in the kernel by reporting NTP-time is sync'd; that's the "11 minutes"
> that you've been seeing.
> https://unix.stackexchange.com/questions/285129/switch-off-11-minute-kernel->
> mode
I was thinking that this was happening, but I wasn't sure exactly why.
> I don't know if dmesg(1) shows this read/write to the RTC.
I'll have a look. I'm waiting to see if disabling the NTP server has truly
fixed this before I do anything else.
> Am I right in thinking that you want the Pi to treat the RTC as
> perfection, never wrong, and never adjust it unless you manually set the
> RTC's time? That the RTC time should be used at boot, and thereafter
> the Pi's own clock maintains the time and the RTC is read or written
> again. Any divergence doesn't matter because the Pi will reboot
> tomorrow and the RTC read afresh.
That's exactly what we want to do. We don't mind if the RTC is a bit wrong
(ie a minute or two, so that we can tie readings to events), but we want all
Pis to have the same time. Eventually there may be three, four or even five
Pis in this system, depending on how many Butts sites we end up with and then
there will be the webserver to provide staff control and Visitor viewing. The
webserver may end up running on the 'master' Pi or the Audio Guide and Quiz
webserver; we haven't done that bit of system design yet.
> You might find an rdate(1) from the slave is simpler at boot time. I
> don't know if Raspbian provides a server for the `time' port, but it's a
> trivial thing.
That looks like a good way to go and a lot less 'messy' than running an NTP
server. I'll have a look into it.
Thanks for your help again.
--
Terry Coles
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