[ntp:questions] leap second warning bits in practice

Marco Marongiu brontolinux at gmail.com
Wed May 13 09:44:37 UTC 2015

On 13/05/15 11:03, Miroslav Lichvar wrote:
> On Tue, May 12, 2015 at 11:33:31AM +0200, Marco Marongiu wrote:
>> On 12/05/15 11:28, Marco Marongiu wrote:
>>> Hi there
>>> In http://doc.ntp.org/4.2.6p5/ntpd.html#leap I read: "If the leap is in
>>> the future less than 28 days, the leap warning bits are set."
>>> What are the practical consequences of the warning bits being set? Will
>>> they cause the leap second to be armed in the kernel eventually? What if
>>> the kernel discipline is disabled?
>> To be a bit clearer, further down it says "When a majority of the
>> survivors show warning, a leap is programmed at the end of the current
>> month". What does that "programmed" stand for...?
> I think it means setting of the leap status that's reported in NTP
> packets and if the kernel discipline is enabled it also sets the
> kernel leap status bits.

Thanks for your answer Miroslav

I don't think it's the case. In the linked doc, the sentence right after
the quoted one says:

"If in the future less than 23 hours, the kernel is armed to insert one
second at the end of the current day"

I understand that the leap second is not armed in the kernel if only the
warning is set. Rather, it seems that the warning is used by a client to
understand if it should believe its upstreams when they claim there will
be a leap second by this month.

I think my interpretation is correct but I'd really appreciate if
someone could either confirm or clarify, so that I/we know exactly what
to expect.

-- bronto

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