[ntp:questions] basic questions about the leapsecond

Martin Burnicki martin.burnicki at meinberg.de
Tue Dec 16 09:19:08 UTC 2008


David,

David J Taylor wrote:
> Unruh wrote:
> []
>> From reading the ntp docs, it seems that if you download the
>> leapseconds file, call it /etc/ntp.leapseconds  and restart ntpd,
>> then ntpd will read that file, and set the leapsecond flag on your
>> system in the last month or day.
> []

Again, the text above refers to the developeer version *only*. 
 
> This seems a lot simpler than the method described in the docs:
> 
>   http://support.ntp.org/bin/view/Support/ConfiguringNTP#Section_6.13.
> 
> which talk about "crypto directory" and "autokey", and seem (to me) a lot
> more complicated than just copying a renamed file and restarting ntpd!

You are right. However, this is how NTP up to the current stable version
works.

> There is also the remark: "If the top level NTP server is unable to obtain
> the leap second file automatically...".  Does this mean that NTP will try
> and fetch this file by itself?

Maybe the dev version. AFAIK no stable version does so.

BTW, you can see if the leap file has been evaluated by running 

ntpq -c rv

and checking the "tai=" value. The NIST leap second file does not only
contain information about the nearest leap second but also about all
earlier leap seconds and thus allows the NTP daemon to compute the
difference between UTC and TAI.

So if the tai value is 0 then the leap file has *not* been evaluated. If the
leap file has been evaluated the displayed value is currently 33.

> Some clarification would be appreciated.

HTH,

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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