[mrtg] Threshold process

Forthofer Russ Russ.Forthofer at ssfhs.org
Tue Mar 23 21:53:55 CET 2010

I am just starting to look at using the threshold process within MRTG.    I set up a sample instance today and ran into a question on the "unbroken" messaging.   In this case, I am monitoring CPU.   The threshold is set to 23.  I have not set the "ThreshHyst" parameter, so I believe this should default to 10%.

 I received a message indicating CPU reached 26.79.   That is as expected.  The next message I received was an "unbroken" message, indicating that the CPU was now at 22.13333333.    I was surprised to see this, as I thought I would not get an unbroken message until CPU was at or below 21.7 (Threshold - 10% of Threshold or 23 - 2.3 = 21.7).

Is my math wrong? Or am I misunderstanding when the unbroken message is supposed to be sent?   Did I misread the default value of ThreshHyst?

The only way I can see that this might be expected is if the ".1" default is applied directly to the threshold, in which case I would get an unbroken notice whenever CPU dropped below 22.9.   But if that's the case, is there a difference in the way this will be applied to, for example, the amount of traffic flowing on a 1G link?

Or is there actually NO default, and so I really need to specify ThreshHyst in all instances?

Thanks for any help in clearing up my confusion!


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