[ntp:questions] Leap second functional question

Unruh unruh-spam at physics.ubc.ca
Tue Feb 19 16:44:42 UTC 2008

David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>Unruh wrote:
>> David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>>> The date error is significant because, once one realizes there are only 
>>> two possible days a year, it becomes unimportant when the flags are set 

>> Well, no, it is still important on those days. It does not occur every year
>> or every day ( in fact I think we have not had one in about 4 years). 

>But you can safely have it set for most of the previous six months and 
>the following six months, whereas the questioner is assuming it must be 
>cleared immediately the leap second has been implemented and not set 
>more than a very short time in advance.  (It certainly has to be set 
>hours in advance, because some clients may not have polled within an 
>hour, and each stratum can extend the propagation delay of the setting 
>of the flags.)
>>> The current code basically checks the date and only sets the bits if it 
>>> is one of those two days.
>> No, it does not. It only sets the bit if it has been told by a majority of
>> its servers that a leap second is coming up. And we had a number of people

You are right. I must admit I did not look at the code, but relied on my
obviously bad memory from a previous thread. Sorry.

... (code proving the bit is set only on June 30 or Dec 31 removed)

>> having trouble in that a leap second seemed to have been announced to them
>> in the middle of Jan this year. Ie, ntp on your system relies on your
>> servers to tell about leap second. It is announce a month before hand and
>> then on the day.

>That tends to confirm that it has been acceptable to set the flag any 
>time after the preceding candidate time.

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