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Re: Leap second reminder - Check your NTP

  • From: Jared Mauch
  • Date: Sat Dec 31 20:44:52 2005

On Sat, Dec 31, 2005 at 05:06:59PM -0800, Roy wrote:
> Kevin Day wrote:
> >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[13742]: 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. is an example:
> >
> > Server dropped: Leap not in sync
> >server, port 123
> >stratum 2, precision -19, leap 11, trust 000
> >refid [], 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.
> >
> >-- Kevin
> >
> 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

	Are they a GPS sync (or do you know?)

	The GPS system doesn't really handle the leap
second situation the same as others, there is a little blurb
here that talks about it:

	I know that I saw my GPS output the following:


	Which is mostly correct, it should have really read 5960 instead.

	I saw my el-cheapo clocks drift by a second at midnight utc.

	I suggest changing your clock sources to something more reliable
if you're seeing folks that are not diligent stratum-1 sources.

	I suggest this as a source:

	I'm kinda curious what CDMA network clocks said around this time
or if they just drifted, i'm sure someone here put their cmda phone in debug
and watched it.

	- jared

Jared Mauch  | pgp key available via finger from
clue++;      |  My statements are only mine.

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