[ntp:questions] ntpd and leap seconds on Windows

Danny Mayer mayer at ntp.isc.org
Wed Oct 12 04:08:51 UTC 2005

Arthur.Porkchop at exemail.com.au wrote:
> As far as I know, the Windows kernel does not support leap seconds.

Nor does Unix. Operating sytems (usually) have no concept of leap 
seconds and wouldn't know what to do with one if it was presented to them.

> Does the Windows port of ntpd try to be clever, by stepping/slewing the
> system clock immediately after the leap second. Or does it wait for the
> next server poll, then wait another 15 minutes before stepping, in the
> usual way ?
It works the same way as on Unix. If you want gory details you need to 
read Dave Mills's papers on the subject. Briefly, ntpd is notified of 
the upcoming leap second event (it's in the NTP packets) and makes 
adjustments to the clock as the time reaches the leap second insertion 
time. You should not notice anything unusual. If you want exact details 
I suggest reading the papers.

> Cheers
> Michael Wouters.
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