[mrtg] Wrong values in log file

[Alex van den Bogaerdt]

On Fri, Jul 04, 2008 at 11:59:57AM +0200, Carlos Fuentes Bermejo wrote:
> Hiya all,
> 
> We are monitoring our Nortel Passport MERS 8610 using MRTG 2.16.2,  
> sometimes we are getting some traffic tips on our graphics, seeing the  
> log file, we realise we are getting some wrong values (lines 4 y 5),  
> anyone knows why we are getting that??? wrong calculations of MRTG  
> when it's getting the values?, or Rateup's problem?
> 
> 
> 1.- Thu Jul  3 21:25:00 2008 38824058 16275266 38867091 16289926
> 2.- Thu Jul  3 21:20:00 2008 37422387 15863370 37432676 18129528
> 3.- Thu Jul  3 21:15:00 2008 37011060 18106572 37046859 18129528
> 4.- Thu Jul  3 21:10:00 2008 35718197 46068673200 36221139 1726944937630
> 5.- Thu Jul  3 21:05:00 2008 36239795 1680893519729 36920764  
> 1726944937630
> 6.- Thu Jul  3 21:00:00 2008 36964506 16766361 38561090 16766361
> 7.- Thu Jul  3 20:55:00 2008 38585197 16759811 39465128 16766361
> 
> Please, any ideas will be welcome.


Multiple processes writing to the same logfile have been mentioned.
This could happen if more than one config file contains the same
name. It could also happen if processes aren't finished before the
next one is started, unless this is prevented by a locking mechanism.

You may be suffering from counter roll overs. If a counter increases
by ${MAXNUM}+something, MRTG will see it as just 'something'.  Now if
at one of the polling intervals the increase is ${MAXNUM}-something
(notice: minus, not plus) then suddenly you think you have a spike
whereas the opposite is true.

The device could give out faulty statistics.  For instance, a single
zero inbetween "123456789" and "123456811" results in a spike of
123456811/300=411522.

And of course bugs can exist in about every other piece of software.

If these problems occur often, perhaps you can keep track of numbers
queried by MRTG, and as soon as a problem occurs you can review the
input to MRTG. That would give you an opportunity to discard either
MRTG or that Nortel Passport switch as the source of the problem.

-- 
Alex van den Bogaerdt
http://www.vandenbogaerdt.nl/rrdtool/