[opensuse] Re: chrony and hwclock

Per Jessen wrote:

I don't use NetworkManager, and my systems run all the time. The
hardware clock is of course UTC, local time is CET/CEST.

So, did you ever run systems with intermittent and unreliable
time-delivered-by-GPS situations and used NTPD in such or similar
environments?

This reads more as in "my systems are almost always on-line and
ntpd works there; it can handle the occasional drop in Internet
connections". It's quite clear that ntpd works there like a charm.

I had big problems in the past when ntpd decides that a time source
is too unreliable and either drops it, or maybe even terminates
itself because all time sources are too much off. I hope that it's
clear that this is not handled by the ntpd service start when the
servers are *not reachable at all* during startup. When they
suddenly appear later on and are off completely, ntpd may lose its
mind. ntpd has also great difficulties when time sources disagree
massively what the time is.

ntpd works great if you have multiple time-sources that are almost
always available and where only quality of connection is managed by
ntpd. The more spurious your connection becomes, and especially the
more bad time source data quality is, the more problematic is its
behavious -- and analysing "why for heaven's sake" the time got
wrong this time is a herculean task that I wouldn't want to do for
an embedded system that is literally off-roads.

In the case of Roger, there is the additional problem that ntpd
uses inherently a polling model for its time sources, with
staggering polling intervals that shall spare the time servers from
overload. AFAIU, Roger needs the complete opposite, a triggering
model that takes into account each available PPS signal. Since I
don't know chrony, I don't know if it delivers that -- but if it
does so, if it is robust, and if the code looks good, I would go
with chrony in the use case that Roger describes.

Cheers,
Joachim

PS: In case this isn't clear: I fought with error analysis in big
ntpd installations over several continents more often than I care
to remember; at least if I want to sleep good at night.

--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Joachim Schrod Email: jschrod@xxxxxxx
Roedermark, Germany

--
To unsubscribe, e-mail: opensuse+unsubscribe@xxxxxxxxxxxx
For additional commands, e-mail: opensuse+help@xxxxxxxxxxxx

Relevant Pages

  • Re: Remaining synced on an unsynchronised peer?
    ... The system doesn't need the greatest possible accuracy, it is more important to the users to detect loss of time sources quickly. ... If other sources are configured NTPD will use them. ... Normally, you would configure four, five, or seven servers which would protect you from the failure of one, two, or three servers. ... A fairly simple script run at intervals of, say, ten minutes could determine that NTPD had lost contact with enough servers to impair its ability to determine the correct time. ...
    (comp.protocols.time.ntp)
  • Re: [opensuse] Re: chrony and hwclock
    ... hardware clock is of course UTC, local time is CET/CEST. ... time-delivered-by-GPS situations and used NTPD in such or similar ... No, never with GPS, but with less-than-100% active connections, yes. ... itself because all time sources are too much off. ...
    (SuSE)
  • Re: clock selection
    ... agreement. ... they both get marked as false ticklers. ... ntpd builds "cliques" of server and looks for overlap and stuff. ...
    (comp.protocols.time.ntp)
  • Alternative algorithms
    ... There has been a good deal of discussion concerning the performance of ntpd. ... It would be more to the point to demonstrate the superiority of some other than "Markovian" algorithm by writing a competing product and demonstrating that it works "better" in some sense. ... Ntpd works slightly less well using internet servers as time sources. ... Ntpd's performance is noticeably better using internet sources during the hours when the internet is relatively lightly loaded. ...
    (comp.protocols.time.ntp)
  • Re: Wifi problems (FC 6)
    ... from the router. ... I still have to give the passphrase after bootup completes. ... ntpd tries to run before there is a connection. ...
    (Fedora)