[ntp:questions] Change reference clock soon after DCF-signal is lost

David Lord snews at lordynet.org
Thu Jul 8 13:41:41 UTC 2010

Matuschka, Sebastian wrote:
> Hi,
> i'm new here and have a question I couldn't answer by myself by
> searching the internet and reading the documentation for hours.
> I have a DCF77 Clock connected to the UART. The line in the ntp.conf
> looks like this:
> server mode 5 prefer
> Receiving the time works, but when I disconnect the DCF77-Receiver from
> the UART, ntpq -p says that ntpd still synchronizes with it for minutes
> (about 4), until it changes to another clock.
> I want that the ntpd changes the synchronization source as soon as no
> signal is received for a few seconds.

The above is normal behaviour in my experience and I see no reason to
change. My MSF receiver has been mostly online since October apart from
a few MSF outages and power cuts. A few minutes to select a different
source doesn't seem too long, and what source is selected is a matter
for ntpd. Extended power cuts take the server off the internet anyway
and minor glitches from packet loss or other network problems means
that ntpd sets stratum 16 and indicates no server suitable for 
synchronisation and servers drop out of pool without giving inaccurate
time. I seem to get very long runs (months) without problem then telco,
isp and electricity supply problems (affecting wide area not just me).


> How can I achieve this?
> The only thing that does something similar, that I can imagine, are the
> minpoll maxpoll parameters.
> But even then (setting them to 4) it will take up to 16 seconds until
> the reference source is changed, correct?
> Best Regards
> Sebastian

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