[ntp:questions] Flash 400 on all peers; can't get ntpd to be happy

Steve Kostecke kostecke at ntp.org
Tue Mar 8 21:18:22 UTC 2011


On 2011-03-08, Chuck Swiger <cswiger at mac.com> wrote:

> Seriously, each physical machine only has one RTC and crystal
> oscillator. It's useful to run one instance of ntpd in the Dom0 (or
> host ESX) context where it can actually work and keep this real
> hardware clock in sync.

NTP disciplines the system (i.e. kernel) clock, not the hardware clock
on the mother board.

> Running ntpd's in the other DomUs/guest VMs is almost entirely
> pointless; it might be useful only if Dom0->DomU time is busted,
> and even in that case, ntpd is unlikely to ever obtain good time
> synchronization running in a DomU.

That's debatable.

I have a Debian 6.0 system running as a VMWare guest. ntpd on this
system has no problem disciplining the clock.

Recent peer billboard snapshot:

steve at www:/var/log/ntpstats$ ntpq -p
remote       refid  st t when poll reach   delay   offset jitter
================================================================
+ntp.my.isp  .GPS.   1 u   34 1024  377   60.665    1.623 1.617
-enob...     .PPS.   1 u 1041 1024  377   39.552   -8.220 2.120
*emit...     .PPS.   1 u  184 1024  377   27.404    3.936 1.347
+yamo...     [snip]  2 u  768 1024  377   33.565   -1.757 2.256
-3snd...     [snip]  2 u  102 1024  377   26.294    7.261 1.179

Peerstats summary (last 10 days):

steve at www:/var/log/ntpstats$ (cat peerstats; zcat peerstats*.gz) | wc -l
2682
steve at www:/var/log/ntpstats$ (cat peerstats; zcat peerstats*.gz) | awk
-f /root/peer.awk 
ident    cnt     mean     rms      max     delay     dist disp
================================================================
[snip]   516   -1.502    1.466    6.665   38.392  960.567 24.501
[snip]   535   -7.244    1.515    8.454   41.862  962.327 23.952
[snip]   532    2.820    1.760    8.235   28.227  956.364 23.869
[snip]   521   -0.673    1.389    8.210   54.179  968.552 24.196
[snip]   534    8.565    1.741    7.829   28.114  955.486 24.080

> You are better off running ntpdate (or sntp) periodically via cron in
> the DomUs.

Perhaps in certain cases, but not across the board.

-- 
Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/




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