[ntp:questions] simulate leap second

Jochen Bern Jochen.Bern at LINworks.de
Fri Dec 27 21:32:51 UTC 2013

On 27 Dec 2013, Williams Catherine wrote:
> I want to simulate leap second case. I have one linux server as NTP server.
> How can I make the server get leap second indicate?

The first question you'll need to answer is whether you can run the
machine(s) in question with their time set to a completely fake one. If
not, your experiments are limited to the actual leapsecond slots -
23:59:60 UTC on the last day of each quarter. (Only the primary slots on
31-Dec and 30-Jun have ever seen *real* leap seconds, but last I
checked, ntpd (still?) did increase the request rate for the secondary
slots as well.)

Note that the next such slot is in only ~100h. You didn't say what
exactly you want to find out, but *if* you cannot use a fake time *and*
the goal is to replicate the mechanisms that will get triggered in a
real leap second while your ntpd is running with its normal setup, I'ld
recommend that you inject the fake leap second into ntpd. (As opposed to
second-guessing the ntpd-to-kernel mechanisms and injecting the fake
leap second directly into the kernel.)

Having that said, the easiest method to inject a fake leap second into
an ntpd is to fake it into a leapseconds file, as ntpd having one set
overrides most of the network announcements mechanisms.


								J. Bern

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