[ntp:questions] Leap second to be introduced in June

William Unruh unruh at invalid.ca
Mon Jan 12 00:16:30 UTC 2015

On 2015-01-11, Michael Moroney <moroney at world.std.spaamtrap.com> wrote:
> If I have a system synchronized with a public NTP source, which is 
> synchronized with an atomic clock that provides leap second info, and
> I am watching carefully, what will happen when the leap second hits?  Will
> my system suddenly find its clock off by 1 second and slowly drift to
> the accurate time provided by the NTP server?

It depends. If that public source is responsible it will pass on to your
system the fact that there is a leapsecond, and your system will "stop"
for a second at the last second of June. But if the public source is
irresponsible, or ignorant, or is google, it may well futz around. Note
that ntpd does not slowly drift, if the time is off by more tha 128ms.
Once your system has decided that it really is off (which takes a while)
it will jump to get rid of the offset (not before having somewhat altered the
drift rate which then needs to be fixed over the next while, I believe.)

f you have a current lepaseond file on board, your system will stop for
a second even if the source has not told it a leap second is coming up.
How the source then handles the leap second and how much of a mess it
makes of your system will depend.

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