[ntp:questions] Lep seconds

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


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
> 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

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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