[ntp:questions] Lep seconds

Martin Burnicki martin.burnicki at meinberg.de
Fri Jan 4 09:48:07 UTC 2008


Mark,

Mark Newman wrote:
> Unruh - thanks for responding.  You are the only one
> who did.
> 
> I certainly did not mean to disparage NTP time.  I
> have spec'ed that it be used on our system.  Where I
> run into problems is when a leap second occurs.
> According to everything I've read when  NTP signals
> the operating system that the second is occurring it
> also outputs time.  It uses the POSIX standard method
> - duplicate a second (or in some cases stretch the
> last second).  This causes confusion when a time
> sample is taken before the leap second and one during
> the leap second.  The UTC standard (which only
> addresses ascii time representations) actually counts
> the second 0..60 rather than 0..59.

If you "normalize" the time with second 60 then you see there _is_ a
duplicate time stamp. This is because a leap second _is_ a inconsistency of
time.
 
> At this point I am obligated to use UTC and NTP.

On most Unix-like kernels NTP just passes a leap second announcement to the
OS kernel, and the kernel handles the leap second in the way it is
implemented in the kernel. For details, please see
http://www.meinberg.de/english/info/leap-second.htm

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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