[time-nuts] Fake leap second ntp servers

Jeff Mock jeff at mock.com
Thu Jan 31 10:58:53 EST 2008

There's probably a good NTP hacker hanging around on this list, but the 
best place to answer your question is probably the NTP hackers mailing list:



Maciej Żenczykowski wrote:
> Hey folks,
> I just joined your email list to inquire about something which some of you
> may have some knowledge of...
> I'm developing some code (for linux with an ntp server/client running), for
> which I would like to verify that it handles positive (and negative)
> leap seconds correctly (I need good time stamps for cross-machine
> synchronization).
> Obviously this is hard to do in practice due to the extreme rarity of these
> events.
> (even more so, considering my home servers running ntp apparently for some
> reason saw leap seconds at the end of 2007...)
> I've thought about switching to djb's suggestion of keeping a non-posix time
> zone on the machines in question, but this
> is not feasible because of existing legacy code...
> Thus I am curious to know if someone somewhere has perhaps set up fake ntp
> servers which regularly insert and delete
> leap seconds (ie. reset their time every couple days and randomly simulate a
> positive or negative leap second 2-3 days
> down the line).
> If not, does anyone know how to go about setting up such a fake ntp server
> for testing purposes?
> Also, is there a known good list of ntp servers which are known to provide
> correct leap second announcements (as mentioned above,
> the stratum 1s at least 2 of my machines were synched to apparently
> broadcast a leap second at the end of 2008).
> I've heard horror stories about time synchronization going haywire the last
> time there was a leap second and some upstream
> ntp servers announced leap-seconds and others didn't (the time
> mis-synchronization brought down the application)...
> Cheers,
> Maciej.
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