[ntp:questions] Preparing for the leap second

Marco Marongiu brontolinux at gmail.com
Wed Jan 11 16:12:06 UTC 2012


So, wrapping up:

Il 10/01/2012 18:12, Marco Marongiu ha scritto:
> I understand from "the NTP timescale and leap seconds" by Prof.Mills
> that modern ntpd doesn't step back the clock but either "freezes" time
> during the leap second, or it slightly increments it at each read until
> the "real time" catches up.

This was confirmed, so I should expect the time on the host to be
monotonic. OK.


> - how can I tell if the operating system will freeze/slowdown, or step
> the clock?

This was not really answered, probably for my own fault. I'll rephrase
the question as follows:

Is there any system tool that will allow me to understand if the system
will freeze/slowdown, or step the clock in the event of a leap second?


> - how can I simulate a leap second, and see how the system reacts?

This was not fully answered. It could be my own fault again. Please let
me know if this could be a good way to test if a given combination
OS/ntpd will behave (doesn't apply to Windows tho).

I should shut down ntpd and configure the node as an "orphan" -- maybe
unplugging the network cable, or shutting down the interface, or setting
no "server" for it... whatever it is.

Then I should set the clock close to midnight, start ntpd again, and ask
the kernel to insert a leap second. Or maybe I should insert the leap
second _before_ starting ntpd?

I understand I could add a fake leap second by using "adjtimex -S", or
by using a fake leapseconds file. Is it correct? Any adjtimex command
line you may want to suggest, or discourage me to use?

Then, I should just watch the clock go, and see if it is monotonic when
midnight comes. Would this be a good way to do that?

while true ; do date +%H:%M:%S.%N ; done | tee time.log

Thanks

-- bronto


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