[ntp:questions] Sudden change in precision and jitter

A C agcarver+ntp at acarver.net
Sat Aug 10 21:02:46 UTC 2013


On 8/10/2013 11:52, David Lord wrote:
> A C wrote:
>> Old thread but new data coming up.  After running for a nice while
>> ntpd finally spun out of control as I've described before.  It swung
>> the clock around and then finally stopped doing anything.  When I
>> finally restarted the clock was over 90 seconds off (the appropriate
>> log entry here):
>> Aug 10 16:23:02 sunipx2 ntpd[23542]: 0.0.0.0 c41c 0c clock_step
>> -95.543901 s
>>
>> I have all stats files turned on so below is a link to a combined file
>> from the configuration, main log, peers (both filtered for ATOM and
>> SHM and an unfiltered version), clockstats, loopstats, sysstats, and
>> rawstats for the time period when the system spun out.
>>
>> Perhaps any of you can spot something that I'm overlooking in these
>> files.  Everything works great and then it collapses very quickly
>> (within one or two polling cycles at most).
>>
>> http://acarver.net/ntpd/combinedlogs20130810.txt
>>
>> If you need/want more data just say so.

>
> Hi
>
> what hit me was your "tos minsane 1"
>
> Both my GPS and MSF sources I'm told cannot be blacked out by
> weather conditions but I also see flying saucers.

In theory my GPS shouldn't get knocked out either.  I've very rarely 
seen it misbehave and certainly not on the order of once every few weeks 
(more like once a year).  I tossed in minsane 1 in the event that my 
connections to the remotes failed so that it would continue with the 
local GPS data (PPS from ATOM and time from SHM).  I think when I first 
started tinkering with it I did have some network problems like that.  I 
know the mindist has helped during flakiness of the whole system when 
things might just teeter on the edge of the default mindist, especially 
the SHM data which moves around by many tens of milliseconds (+/- 70ms 
is fairly common).

The billboard on the system right now after having restarted it a few 
hours ago looks fairly normal:

associd=0 status=011d leap_none, sync_pps, 1 event, kern,
version="ntpd 4.2.7p270 at 1.2483-o Sun Apr  1 07:58:59 UTC 2012 (1)",
processor="sparc", system="NetBSD/5.1", leap=00, stratum=1,
precision=-13, rootdelay=0.000, rootdisp=50.195, refid=PPS,
reftime=d5b12777.e1de3481  Sat, Aug 10 2013 20:56:23.882,
clock=d5b12785.46699541  Sat, Aug 10 2013 20:56:37.275, peer=39391, tc=4,
mintc=3, offset=0.013, frequency=-74.925, sys_jitter=0.122,
clk_jitter=0.010, clk_wander=0.015, tai=35, leapsec=201207010000,
expire=201312280000
      remote   refid      st t when poll reach   delay   offset  jitter
======================================================================
oPPS(0)       .PPS.       0 l   14   16  377    0.000    0.013   0.122
-SHM(0)       .GPSD.      4 l   16   16  377    0.000   52.092   5.353
+v v                      2 u  163  512  377   40.618    1.243   0.422
+w w                      2 u   26  512  377   34.010    1.060   0.528
-x x                      2 u   98  512  377   93.175    0.418   0.352
-y y                      2 u  536  512  377   77.223    2.690   2.236
+z z                      2 u  143  512  377   85.161    0.621   0.231


I just can't figure out what causes the issue since it's very random. 
Sometimes it can go weeks or months without issue and other times it can 
crash in days.


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