[ntp:questions] Re: Question about ntp log messages and logging interval

Richard B. Gilbert rgilbert88 at comcast.net
Tue Sep 12 18:23:10 UTC 2006

Jeff Boyce wrote:
> Greetings -
> I am using NTP on a fully up to date RHEL3 system (Dell PE2600 
> hardware).  I use a very basic configuration file (see below) and also 
> use the North America NTP pool servers.  Since I got ntp running 
> properly (I think) about two weeks ago, I notice a lot of ntp 
> information in my log file (see log snippet below).
> 1. I am wondering if this is an indication of a properly (or improperly) 
> running ntp system?
> 2. If this logging is normal, are there any recommendations for how I 
> can reduce the amount of logging?
> 3. How do I find out what the standard polling interval is, and how 
> would I reduce the interval if I wanted to?
> Thanks.
> #/etc/ntp.conf
> server 0.us.pool.ntp.org
> server 1.us.pool.ntp.org
> server 2.us.pool.ntp.org
> server     # local clock
> fudge stratum 10
> driftfile /var/lib/ntp/drift
> # ntpq -p
>     remote           refid      st t when poll reach   delay   offset 
> jitter
> =====================================================
> LOCAL(0)        LOCAL(0)        10 l   18   64  377    0.000    0.000 0.015
> *dns01.flame.org clock.xmission.  2 u   19   64  377   73.882    8.660 
> 42.399
> +216-136-10-198. ns.nts.umn.edu   3 u   30   64  377  112.790    9.468 
> 48.783
> +sfobug.org   2 u   16   64  377  113.669   15.344 
> 40.253
> ********* /var/log/messages ***********
> Sep 10 04:46:26 bison ntpd[20484]: time reset 0.842745 s
> Sep 10 04:46:26 bison ntpd[20484]: synchronisation lost

That does not look like a happy system to me!  Your ntpq "banner" shows 
high values of jitter and long round trip delays.   Since you are using 
pool servers, this is not exactly under your control but it is not good. 
  The best servers are those close to you in "net space" because the 
error in transmitting time from server to client is limited to one half 
the round trip delay.  It is usually much less than that but can't 
possibly be greater.

The high jitter figures say that, if one of those servers were to send 
you a packet every second, the packets would not arrive at exact one 
second intervals.  It's highly improbable that they would in any case 
but your internet connection seems to be introducing quite a bit of 
randomness in the transmission times!

What can you do?  Try to find a server or two with a round trip delay 
less than twenty milliseconds.  Servers should be physically close to 
you; if you are in Los Angeles, don't consider servers in New York City!
It may not be possible to find better servers than the ones you are 
using; good servers are in short supply!  If you really need, or want, 
precise time you could do as I and many others have done; buy a GPS 
timing receiver and operate your own stratum one server.  Or try a 
better internet connection.

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