> On Mon, Nov 09, 2015 at 09:57:48PM +0100, Didier Kryn wrote:
>> Le 09/11/2015 20:12, Rainer Weikusat a écrit :
>>> After booting, the discrepancy between the RTC clock and the actual time
>>> is unknown.
>>      I remember having had a problem with two servers when the time
>> discrepency reached 5mn (It was for kerberos authentication). We
>> discovered that one of the two was not synchronized by NTP at all.
>> The problem showed up after 4 years with many reboots and no clock
>> adjustment on the non-synchronized host.

>>      NTP does not adjust the RTC brutally; it seems to adjust slowly
>> the frequency so that synchronization happens without the process
>> being noticeable to other apps - it can take hours. On shutdown it
>> saves the RTC settings in /var/lib/ntp/ntp.drift, and (AFAIU)
>> /var/lib/hwclock/adjtime. After some days of running NTP, your RTC
>> is well trimmed and does not drift much. It does not stop running
>> when you power-off your computer. Therefore, at startup the
>> discrepancy is very small - unless the battery of the RTC is dead or
>> you stopped the computer for a year.

>>      Everything above is non-authoritative; it is the result of my
>> own observations.
> I used chrony as my NTP client.  If the discrepancy between local time
> on the machine and the correct time, it just gave up.  I/m not sure at
> what discrepancy this happened, but it helped a lot to explicitly set
> the time by my watch.  Once the time was properly synced, though,
> chrony worked well to keep it correct.