[ntp:questions] Re: What went wrong with the leap second

Rob van der Putten rob at sput.nl
Wed Jan 4 15:18:00 UTC 2006


Hi there


Martin Burnicki wrote:

> This indicates that either the NTP daemon itself, or its upstream server(s),
> may not have received the leap second announcement, and so time
> synchronization has been messed up.
> 
> Please have also a look at my posting from Jan 3 in the thread with the
> subject "Drift handling...".

Interesting.

> I don't know exacly what you mean here.

The idea is to mask the leap second;
Instead of adding a second you just make the seconds longer.

> Normally ntpd just passes the leap
> second announcement to the operating system kernel, and the way the leap
> second is handled depends on how this is implemented in the OS kernel
> clock.

> DCF77 starts announcing the leap second 1 hour before it is inserted.
> 
> The GPS satellites start broadcasting the upcoming leap second shortly after
> this has been announced by the IERS. The last leap second has been
> announced by the GPS satellites since middle of July, 2005.

I only saw them on the 31st.

> How these announcements are passed to ntpd depends on how the leap second
> announcement is handled by the firmware of the DCF77 or GPS receiver, how
> the driver module for that particular device evaluates that announcement
> and passes it to the ntpd loop filter, and of course by the version of
> ntpd, since there have been some modifications across the versions.

> Not that I'm aware of. It this has happened this was a bug.
> 
> Normally ntpd works exclusively with UTC, but on the other hand I know there
> are people who think this is not what they need, and pass a reference time
> to ntpd which is local time rather then UTC. Such an ntpd might distribute
> local time rather than UTC, and since ntpd was not aware of this, it would
> insert the leap second at what it thinks is UTC midnight, but in fact is
> local time midnight.
> 
> Maybe our leap second info page is helpful. Please have a look at
> http://www.meinberg.de/english/info/leap-second.htm
> 
> Hope this helps.

Not much.
Thanks anyway.

The problem was that I configured 4 of my ISP NTP servers as sync source.
They don't use their own GPS / DCF77 / whatever receivers but use several
other NTPDs to sync to.
I think some of their time sources broke and polluted their own time and
that of their customers.

I was hoping that one could piece together exactly what has gone wrong.
Right now I don't think that this is ever going to happen.

The only way that one can avoid these problemes is probably to use ones own
GPS receiver instead of somebody elses NTPD.


Regards,
Rob
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