[ntp:questions] ntpd losing sync

A C agcarver+ntp at acarver.net
Sat Feb 4 09:23:27 UTC 2012


On 2/4/2012 01:11, Harlan Stenn wrote:
> A C wrote:
>
>> Here's the current configuration for version 4.2.7p236:
>>
>> server          0.us.pool.ntp.org minpoll 9 iburst
>> server          1.us.pool.ntp.org minpoll 9 iburst
>> server          0.north-america.pool.ntp.org minpoll 9 iburst
>
> You might try replacing the above 3 lines with:
>
>   pool us.pool.ntp.org minpoll 9 iburst
>
> I do not remember offhand if iburst is supported for the "pool"
> directive but give it a shot.
>
>> server ntp1.gatech.edu prefer minpoll 9
>
> Is this server close enough that you want to "prefer" it?

It's usually pretty stable, more stable than some of the pool servers 
that I get which is why I have it set to prefer.

>
>> server rolex.usg.edu minpoll 9
>> server  127.127.22.0  minpoll 2 maxpoll 4
>> fudge   127.127.22.0  time1 +0.000 flag2 1 flag3 1 refid PPS
>
> 0.0 is the default for time1.
>
> flag2 1 means PPS capture on the falling (clear) edge of the pulse.
>
> flag3 1 enables the kernel PPS discipline.
>
> I haven't been following this thread - what OS are you using?

The time1 flag is in there from a point when I was fiddling with it on 
PPS.  I just left it in there, I know the default is zero.  I need flag2 
for the system to detect the pulse because it is inverted.  Kernel PPS 
is enabled because I have compiled the kernel for PPS so that's correct, 
too.  All of this is NetBSD 5.1 on sparc.

>
>> server  127.127.28.0  minpoll 7 noselect
>> fudge   127.127.28.0  time1 -0.6 refid GPSD
>
> OK, GPSD via the shared memory driver, and "noselect".  Nasty jitter on
> this one...

Yes, it does have a lot of jitter that I've been trying to monitor which 
is why I had the noselect in place.  Eventually I may remove noselect 
and just fudge its stratum to avoid using it unless necessary.

>
>> The peer list after waiting about a day from the initial system upset:
>>
>>      remote           refid     st t when poll reach  delay  offset  jitter
>> ==========================================================================
>> x127.127.22.0   .PPS.           0 l    -   16  377   0.000 -465.49  355.933
>>   127.127.28.0   .GPSD.          0 l    -  128  377   0.000 -208986  2833.87
>>   207.7.148.214  216.218.254.202 2 u    -  512  377 1045.07 -209713 11784.0
>>   72.14.179.211  127.67.113.92   2 u    -  512  377 1029.80 -201710  6559.37
>>   173.255.224.22 128.4.1.1       2 u  245  512  377 919.628 -202629  7684.05
>>   130.207.165.28 130.207.244.240 2 u    -  512  377 994.543 -204125  7778.28
>>   131.144.4.10   65.212.71.102   2 u   23  512  377 1000.21 -203648  7687.63
>>
>> Note that the offset for PPS is swinging wildly, not exactly visible in
>> this static snapshot.
>
> What's with the delay numbers?  Are you on a network link that is
> saturating?


No, my link shouldn't saturate.  I do have an asymmetric DSL but the 
downstream rate is consistently above 22 Mbit/sec and upstream is 5 
Mbit/sec.  I keep an eye on the rate through the router and it's fairly 
flat with only occasional spikes.  In the past 24 hours the largest data 
spike was 240 kbyte/sec (2.4 Mbit/sec) downstream for about one minute. 
  The upstream at that time was nearly zero.  For the same 24 hour 
period, the largest upstream spike was about 10 kbyte/sec (100 
kbit/sec).  The delays are normally pretty good usually staying below 
100 milliseconds.  I only see delays like that when everything goes haywire.


I've been watching the log file now that I just restarted ntpd and am 
noticing a lot of spike_detect messages.  The clock is stepping around 
and the entire peer list refreshes, resetting the reach flags to zero 
for everything, dropping all syspeers and acting like it's starting over.


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