[ntp:questions] Leap Second

Unruh unruh-spam at physics.ubc.ca
Wed Dec 3 07:10:38 UTC 2008


morsupil <michael.froment at gmail.com> writes:

>On 3 d=E9c, 00:30, Bill Unruh <un... at physics.ubc.ca> wrote:
>> Unruh <unruh-s... at physics.ubc.ca> writes:
>> >michael.from... at gmail.com writes:
>> >>Hi all,
>> >>Since yesterday I saw the leap second Flag set on some servers of
>> >>ntp.pool.org. I'am quite surprise because the leap second add to be
>> >>set the 31/12/2008 and not the 1/12/2008.
>> >>Is it normal????
>> >The leap is announced at the beginning of the month to make sure that al=
>l
>> >ntp clients know about it. It always occurs at the end of the month ( I
>> >think ntpd has it hard coded as the end of June or Dec, but in principle=
> it
>> >could be any month)
>>
>> Here is a fragment from the ntp code (ntp_loopfilter.c) (4.2.4p4)
>>
>> if ((tm->tm_mon + 1 =3D=3D 6 &&
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 tm->tm_mday =3D=3D 30) || (tm->tm_mon +
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 1 =3D=3D 12 && tm->tm_mday =3D=3D 31)) {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (leap_next & LEAP_ADDSECOND)
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ntv.status |=3D STA_INS;
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0else if (leap_next &
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0LEAP_DELSECOND)
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ntv.status |=3D STA_DEL;
>>
>> Ie, ntp pays attention to the leap second flag only if it is June 30 or D=
>ec
>> 31. Now, that is not correct since I believe that a leapsecond can occur =
>on
>> any month, but the tradition is that if there is only one or two a year,
>> those are the dates chosen. In a century or two, when there are more than=
> 2
>> per year, then ntpd will run into trouble. (Of course the definition of
>> time might have changed anyway, or the whole UTC kludge may be scrapped o=
>r
>> a new edition of ntpd not containing that assumption may be published.)
>> Note that the very existence of ntpd with its assumptions puts huge
>> pressure on the standards organisation to comply with the assumptions.

>So this could not cause problem if on a pool of servers someone answer
>with the LI flag set and another one without the LI flag set????
>I'm quite surprise by the fact that ntpd seems to be the standard...
>There is many of other client and many of other servers...

Just to clarify: the standrds say that Dec 31 and June 30 are the preferred
dates, March 31 and Sep 30 the secondary ones. I assume once we get to the
24th century once we need more than 4 leap sec a year, standards will have
changed.




More information about the questions mailing list