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Re: Leap second reminder - Check your NTP
- From: Roy
- Date: Sat Dec 31 20:08:24 2005
Kevin Day wrote:
There is at least one stratum-1 server here on the West coast that my
NTP says is now off by 1 second. Several stratum-2 are synced to it and
are now off also. So checking servers might be a good idea
Last NTP spam:
I'm by no means an NTP expert, if anyone else is, please pipe up.
About 30 minutes before the leap second should have occurred, several
of our systems reported "xntpd: time reset 0.958385 s", which
was really strange. They moved the wrong direction, and they did it
early. Shortly after, those systems lost ntp association and began
drifting. About 10 minutes after midnight all have regained sync. I
wasn't checking things that early to see why, it's possible some of
our NTP sources started disagreeing on what the correct time was, and
would also match what other people have reported off-list, going back
as far as 18 hours before midnight.
Several public NTP sources are now indicating a "leap second alarm"
(setting the leap bits to 11), which will cause most NTP clients to
rule them out as a source. ntp-2.gw.uiuc.edu is an example:
220.127.116.11: Server dropped: Leap not in sync
server 18.104.22.168, port 123
stratum 2, precision -19, leap 11, trust 000
refid [22.214.171.124], delay 0.03357, dispersion 0.00049
According to ntpdate, its clock seems to have stopped about 5 minutes
before midnight, and hasn't yet recovered.
Other NTP servers haven't cleared their "today is a leap second day"
bit, which they should have by now. Some NTP implementations rule out
servers that don't agree with what their "master" server thinks the
leap second bits should be. My reading of the NTP spec says that at
00:00:00 the leap bits should have been returned to zero. Attempting
to sync from one of these servers will produce a "Next leap second
occurs at 00:00:00.000 UTC Sun Jan 01 2006" message, but that should
be harmless as long as they correct themselves a while before midnight.
Still others have their clocks off by a significant amount(10+
minutes) and think they're still in sync, but since I started typing
this email, they all have corrected themselves.
While I can't say anything broke on our network as a result of the
leap second, a good percentage of our gear lost NTP sync or had some
kind of NTP problem around midnight UTC. You may want to check your
NTP status at some point, in case something drifted quite a way off
and won't step itself back now because the difference is too great.