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.
Didier
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