[ntp:questions] Preparing for the leap second

unruh unruh at invalid.ca
Wed Jan 11 17:28:00 UTC 2012


On 2012-01-11, Marco Marongiu <brontolinux at gmail.com> wrote:
> 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?

If you told us what operating system you were using, more useful
suggestions might follow. YOu now have the answer for windows.
Whichoperating system are you using? Or do you want us to keep guessing?

>
>
>> - 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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