[ntp:questions] Re: Leap second talks are postponed

Danny Mayer mayer at ntp.isc.org
Tue Nov 22 17:37:56 UTC 2005

David L. Mills wrote:
> David,
> The implementations including my code do not step the clock, just stop
> if or allow it to progress slowly during the leap second itself. If what
> you mean by slewing is to force the clock to amortize the second at
> "normal" slew rate, say 500 PPM, then the clock would be in error very
> close to one second following the leap and take the better part of one
> hour to resume expected accuracy. Meanwhile, NTP would scream and holler
> because the step threshold would be exceeded. Of course, should you be
> concerned about step corrections and forbid them as configuration
> option, your applications would have to be content with the large error
> during the amortization interval.
> I'm not being facetious here; consider the advice of the IBM mainframe
> community when running local time. For the DST spring forward, no
> problem - just set the clocks ahead one hour in every timezone. For the
> fall fack, stop the applications and turn the machine off for four hours
> while all the clocks in the country survive the step. Of cource, should
> we ever have a leap second deletion, then the slew issue will occur in
> earnest.
> Dave

Of course, IBM mainframers' advice would only be valid in the USA
Mainland, ignoring such faraway place as Hawaii. Were you to talk about
Russia, you'd be in even deeper. And we won't talk about what you'd do
if you were an International company and had operations in England and
Australia where the time zones would be moving in opposite directions...


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