Microwave Biscuit

Load Averages

Posted in Linux, ubuntu by microwavebiscuit on June 10, 2007

I almost always have “top” running on one of my desktops as a means of making sure no processes are running away or hogging memory, etc. Occasionally I’ll find that FireFox has sprung a leak and is using 500Mb of RAM or something. That usually indicates that it will crash at some point in the near future and if I really care about what I’m looking at I should bookmark it and restart FF. Obviously there are other processes that can run away and/or that need monitoring which is why I keep top running.

One of the statistics that I’ve seen but didn’t really understand was Load Average. For example, right now in my “top” window at the upper right is the following:

load average: 0.26, 0.38, 0.33

I previously had no idea what those numbers meant other than to know that if I’m encoding audio or video, running lots of stuff, etc. those numbers go up. When nothing is happening on my machine, the numbers come back down. So it is measuring some sort of load on the system. I decided to look around the web today to see what I could find out.

Here’s the deal, the reason there are three numbers is that they represent the last minute, the last 5 minutes and the last 15 minutes. They are more like trends on the system. Basically when I copied those numbers out of top my system had used 26% of the CPU in the last minute, 38% of the CPU over the last 5 minutes and 33% of the CPU over the last 15 minutes. If any of those numbers are over 1.0 that generally means that stuff is waiting and/or your system is bogged down.

There are much more detailed explanations available on several sites that determine exactly how the numbers get calculated but I was able to get a rough sense of what they mean and why there are three.

Helpful links:

Wikipedia entry
Really geeky article

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