[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...".


> 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.

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