[ntp:questions] Leap Second on NTP server at stratum 2

Jochen Bern Jochen.Bern at LINworks.de
Wed Jun 10 14:42:53 UTC 2015

On 06/10/2015 01:27 PM, Kashif Mumtaz Tahir wrote:
> Dear Macro,
> We just want to sync seamless with leap seconds. [...]
> Should we need to change/tune anything.

I read your description as:
-- There is a GPS device that actually *speaks NTP* (as opposed to,
   e.g., being connected to a server with a serial cable)
-- This device feeds a central stratum 2 server running ntpd
-- Everything else of interest is an NTP (not SNTP) client of
   that central server
-- No special configs beyond the above, in particular,
   -- no additional external NTP servers,
   -- no leap seconds file, and
   -- no suppression of stepping
   configured on any of the machines.

My conclusions:
-- Whatever announcement the GPS unit makes of the upcoming leap second
   will be forwarded to the various machines.
-- You hopefully have historic records, vendor statements, or whatever
   indicating that this GPS unit *will* announce a leap second to be
   (It mistakenly announcing a *negative* leap should be highly
   improbable, but I have no idea how likely it is to find a GPS unit
   that flat out doesn't propagate leap second announcements.)
-- The job of actually "executing" the leap second will be left to the
   OS kernel of every individual machine - if you cannot afford them
   hitting a historic or new bug that night, you should start testing
   kernel versions with simulated leap seconds ASAP.
-- There is a (very small) chance that in the leap second night, your
   single-point-of-failure GPS unit will somehow cease to work before
   any announcement happens and your platform will never learn of the
   upcoming leap second - in which case you'll find it working but
   being offset by one second in the morning.

								J. Bern
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Jochen Bern, Systemingenieur --- LINworks GmbH <http://www.LINworks.de/>
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