The Multi Router Traffic Grapher is a powerful tool to generate graphs for various kinds of system information. The most commonly used backend is snmp, whose network ability actually is the reason for the M in MRTG. Besides using snmp as the data source, one can run regular scripts outputting data to be graphed. The following shows the local setup for nwl.cc.

Easy as eatin' pancakes: simply install MRTG and your preferred snmp implementation (net-snmp in my case).

Basically, the following things are needed:

• a single MRTG config for each graph to generate
• a cron job to update the graphs values
• a destination directory for the graphs and the index.html (auto-generated)

Create the directory /etc/mrtg, which will contain all the configs.

There are two ways to get a config for MRTG: either using cfgmaker (shipped with MRTG) or create by hand, which of course is the more flexible way. cfgmaker on the other hand is used best when creating graphs for network interfaces, as the output is quite nice without much effort necessary.

To generate configs for all local NICs, use something like this:

cfgmaker --output=/etc/mrtg/traffic.cfg --ifdesc=ip --ifref=descr \
	--global "WorkDir: /var/www/nwl.cc/htdocs-secure/mrtg" \
	--global "Options[_]: bits,growright" public@localhost

Note that this will generate the config as /etc/mrtg/traffic.cfg, and assumes that the output directory for the graphs is /var/www/nwl.cc/htdocs-secure/mrtg. Also this obviously uses snmp as backend, so won't be usable without an snmpd running locally.

As sample for a manually created MRTG config, this one is used to monitor CPU load:

WorkDir: /var/www/nwl.cc/htdocs-secure/mrtg
LoadMIBs: /usr/share/snmp/mibs/UCD-SNMP-MIB.txt
Target[localhost.cpu]:ssCpuRawUser.0&ssCpuRawUser.0:public@localhost
	+ ssCpuRawSystem.0&ssCpuRawSystem.0:public@localhost
	+ ssCpuRawNice.0&ssCpuRawNice.0:public@localhost
RouterUptime[localhost.cpu]: public@localhost
MaxBytes[localhost.cpu]: 100
Title[localhost.cpu]: CPU Load
PageTop[localhost.cpu]: <H1>Active CPU Load %</H1>
Unscaled[localhost.cpu]: ymwd
ShortLegend[localhost.cpu]: %
YLegend[localhost.cpu]: CPU Utilization
Legend1[localhost.cpu]: Active CPU in % (Load)
Legend2[localhost.cpu]:
Legend3[localhost.cpu]:
Legend4[localhost.cpu]:
LegendI[localhost.cpu]:  Active
LegendO[localhost.cpu]:
Options[localhost.cpu]: growright,nopercent

Notes:

• Adding MIB descriptions to the LoadMIBs parameter allows for using symbolic names in the Target description. BUT there is no support for auto-loading included MIB descriptions by the specified ones, so the desired description has to be parsed manually for any INCLUDE directives and the mentioned descriptions have to be added right before the desired one to the LoadMIBs option.

The cron job is quite simple to create since we assume all active configs are kept inside /etc/mrtg, ending with .cfg:

#!/bin/sh

mrtg="/usr/bin/mrtg"

for conf in /etc/mrtg/*.cfg; do
        $mrtg ${conf}
done

You can save this script where you want to, I just saved it in /etc/mrtg, too.

To make the job active, add the following line to /etc/crontab:

*/5 * * * *     /etc/mrtg/cronjob.sh 1>/dev/null

(replacing the path to and name of the script from above, if necessary).

First, the graphs initially have to be created. This is done by simply executing the cron job three times manually. Then a simple call to indexmaker should to the rest:

indexmaker --output=/var/www/nwl.cc/htdocs-secure/mrtg/index.html \
	--title="System Graphs Powered By MRTG" \
	--sort=name --enumerate /etc/mrtg/*.cfg

• Gentoo Howto: SNMP & MRTG made in easy