[Xymon] How is clock graph in "trends" column generated

[J.C. Cleaver]

On Wed, June 22, 2016 10:56 am, Junaid Shahid wrote:
> Hello Xymon Gurus!
>
> I have searched the interwebs for it but could not find anything useful.
>
> My question is how are the values calculated for the Clock offset graph,
> displayed at the bottom of the "Trends" column. I have seen some posts
> (and
> my experience also confirms this) that Xymon's ntp check (specified in the
> hosts.cfg) is only to see if NTP daemon on a client is up (responsive).
> While the clock offset is plotted via some internal logic (client feeds
> data to the server).
>
> Would really appreciate if some one can throw some light on it!
>
> Some links that I have gone through:
> http://osdir.com/ml/monitoring.hobbit/2007-03/msg00361.html
> http://lists.xymon.com/oldarchive/2009/01/msg00417.html
>

Hi,

The "clock" value is computed from the timestamp of the client message (as
seen at the end of generation by the client) to the timestamp of the "cpu"
status message generation by the xymond_client on the server. (It's thus
dependent on your xymon server having the time set correcty.) The client
isn't doing a comparison itself against anything externally.

This is subject to skew if:
a) your xymon server itself is wrong
b) you have a xymonproxy in the middle and messages are delayed getting to
xymond
c) your xymond_client process is backlogged with [client] messages
d) your xymon server is overloaded and has a long period between
transmission and TCP processing by xymond

For b) and c) the 4.4 version (and the Terabithia RPMS, IIRC) use receipt
time for the first proxy encountered, and xymond parsing/separation time
otherwise, for comparison, which fixes both of those things. Local ntp
problems and "raw" TCP lag until connection receipt will still affect
things, however.

One "feature" of this in 4.3 though is that if you see clock skew rising
and times are correct on both sides, then you can easily tell that your
xymon server is having performance problems.


HTH,
-jc