Lukas Beeler's IT Blog

As discussed in the previous post, you can gather temperature data from RSA II or iLO cards using SNMP quite easily.

While the data itself can be good enough to make a decision, executives in a company always like nice diagrams. So my first try was to load the CSV-like datafile generated using said script into Excel, and make a diagram out of it. But Excel is restricted to 255 parameters per axis, which was severely limiting.

I’ve been using Cacti for quite some time, but wasn’t willing to implement it because we’re mostly a Windows shop, and my plan was to integrate the linux boxes into Operations Manager 2007. Cacti uses Tobi Oetiker’s rrdtool to create the graphs.

Creating graphs using rrdtool is quite easy, actually. I wrote a simple script that handled this:

makerrd

Creates the appropriate rrd file. Replace the unix timestamp as appropriate. The last value on the RRA lines is the number of values saved into the data file.

#!/bin/sh
rrdtool create test.rrd           \\
           --start 1176465000     \\
           -s 300                 \\
           DS:temp:GAUGE:600:U:U  \\
           RRA:AVERAGE:0:1:5000

inputrrd

Loads the data from the simple CSV-like file into the RRD file. The more elegant approach would be to load the data directly from SNMP into the rrd database, but i’m no programmer.

#!/bin/zsh
while IFS=';' read timestamp temp ; do
        temp=`echo $temp | sed 's/\\..*//;'`
        rrdtool update test.rrd ${timestamp}:${temp}
        if [ $? != 0 ] ; then
                rrdtool failed
        fi
done < machine

makegraph

Creates a graph from the data in the rrd file. The HRULE lines create lines for error margins. In this case 35C and 30C.

#!/bin/sh
rrdtool graph temp.png                       \\
        --start 1176465385 --end `date +%s`  \\
        DEF:mytemp=test.rrd:temp:AVERAGE     \\
        LINE2:mytemp#0000FF                  \\
        HRULE:35#FF0000                      \\
        HRULE:30#FFA500

See the created graph to the right. Of course, rrdtool has much more options and can create much nicer graphs.