Check_load

Derek J. Balling deballing at vassar.edu
Wed May 10 12:51:32 CEST 2006



On May 10, 2006, at 6:42 AM, Sandeep Narasimha Murthy wrote:


> Can anyone please provide a brief idea on how check_load works and  
> on the data it provides. The data provided is in the format load  
> average: 1.62, 1.67, 1.74, which doesn’t make a lot of sense. I  
> googled on this and ended up getting even more confused.

"load average" is the number of processes (average) in the wait state  
over a given period of time. For most UNIX machines, the periods are  
usually 1, 5 and 15 minutes. (e.g., in your example, in the past  
minute an average of 1.62 machines were waiting for a CPU, in the  
past five minutes, 1.67, and in the past 15 minutes, 1.74).

In the example you give, it would appear your machine is catching up,  
as the short-term averages are lower than the long-term averages, but  
it all depends on your applications that are running, what cycles  
they demand CPU on, etc., etc.

> The reason behind my question is that we are also using CACTI for  
> monitoring the systems and it shows a 100% CPU load since last  
> night while Nagios didn’t raise any alarm at all. I have to find  
> out whether it was a false alarm or there is a problem with my  
> Nagios setup ..
It's confusing to refer to "100% CPU load" since load isn't measured  
in percentage (at least not in this case, not usually). Referring to  
it as 100% CPU usage, or utilization, might be better.

For example, it's possible to have a CPU load of "0" and usage of  
100%. How? If I've only got one process making use of CPU cycles, and  
it's getting 100% of the CPU. If there's nothing else waiting for  
CPU, the "load" will not be high, even though the usage (from the  
single running process) will be.

In other words, CPU usage isn't necessarily as important as load is,  
although it certainly can be a factor in determining the cause of  
Load (because processes which are waiting on Disk I/O, or swap, also  
contribute to load).

Hope this helps.

Cheers,
D


--

Derek J. Balling
Systems Administrator
Vassar College
124 Raymond Ave
Box 13 - Computer Center 217
Poughkeepsie, NY 12604
(845) 437-7231


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