RE: [chrony-users] Chrony offset and stability adjustments?

["LeBlanc, Daniel James" <daniel.leblanc@xxxxxxxxxxxxx>]

Hi Bill.

Thanks for your quick reply.  I have done a bit of searching and have not been able to find anything regarding how we can improve the root dispersion (as you have described).  Based on the description of how root dispersion is calculated (https://serverfault.com/questions/768280/what-is-ntp-dispersion-and-how-do-i-control-it - see ladder diagrams and associated description half way down the page), even reducing the polling interval on the local server will not improve the calculated root dispersion amount.  Is there anything that can be done short of using a closer and lower stratum NTP server as a source to further reduce the root dispersion?

Thanks.

Daniel J. LeBlanc, P.Eng., MBA, DTME | Senior Network Architect | Bell Canada

-----Original Message-----
From: Bill Unruh [mailto:unruh@xxxxxxxxxxxxxx] 
Sent: January-04-19 4:08 PM
To: chrony-users@xxxxxxxxxxxxxxxxxxxx
Cc: LeBlanc, Daniel James
Subject: Re: [chrony-users] Chrony offset and stability adjustments?



William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/

On Fri, 4 Jan 2019, LeBlanc, Daniel James wrote:

> 
> Hello All.
> 
>  
> 
> I have a number of chrony instances deployed on VMs.  In each case, they stabilize with a somewhat
> stable root dispersion as reported by ‘chronyc tracking’.  I have the following questions as I have
> not been able to find answers online or within the chrony documentation:
> 
>  
> 
> 1.       I am ourcing my time from NTP servers that have a consistent root dispersion of between 1
> and 2ms.  Is it possible for me to tell chrony to offset the local clock by this amount?  I have
> tried the ‘offset’ setting but it does not appear to have had any affect on the root dispersion as
> reported by ‘chronyc tracking’.

That dispersion of 1 or 2 ms does not mean that the clock is consistantly out
by 1 or 2 ms. It means that the time bounces around the "true time" by about
that amount. Ie, you cannot compensate for it. If you could the remote clock
would have done so.

> 
> 2.       My chrony server root dispersion appears to “adjust” more readily than I would like (within
> the logs, I can watch the root dispersion grow from 1ms to 1.5ms, then adjust back when it switches
> to another NTP server).  Can I change a setting so that it makes adjustments much more slowly?

Again, you seem to be confused as a what the dispersion means. It is a measure
of how much the time of the remote clock bounces around the real time, not a
measure of offset. Less bouncing around is good, You would like it to be 0 and
as rapidly as possible. But as with all measurements it will never be 0.


> 
>  
> 
> Thanks.
> 
>  
> 
> Daniel J. LeBlanc, P.Eng., MBA, DTME | Senior Network Architect | Bell Canada
> 
>  
> 
> 
>
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