Software thoughts

In this post, I show how to install and use MRTG, a graphical tool to monitor the traffic load on network-links.

The manipulations described here apply to linux Ubuntu 7.10 Gusty.

As prerequisite, perl and apache need to be installed.

To get MRTG and its database rrdtool, install the binary packages:

apt_get install mrtg
apt_get install rrdtool
apt-get install librrds-perl

To check the install, just type "mrtg" as root in a console. (tip: on Ubuntu, "type sudo -s" to keep a console logged as root and not to have to precede each line with "sudo")
You may get the following error occurred:

-----------------------------------------------------------------------
ERROR: Mrtg will most likely not work properly when the environment
variable LANG is set to UTF-8. Please run mrtg in an environment
where this is not the case. Try the following command to start:

env LANG=C /usr/bin/mrtg
-----------------------------------------------------------------------

Then just type:

export LANG=C

If you type "mrtg" again, you should have no output, because it waits for a config file in parameter.

MRTG gets its data from an SNMP server, so you need one.
If you decide to analyze a router, make sure SNMP is enable. If you monitor your local machine,
You may need to install "snmpd"

To install the server :
apt-get install snmpd
and the client :
apt-get install snmp

After snmpd install, you can check it is running
ps -A | grep snmpd

To configure SNMP, you can either edit /etc/snmp/snmpd.conf
or more simply run the following command:
snmpconf -g basic_setup

This utility prompts questions about the equipment to monitor with SNMP and generates the config file.

Restart snmpd :
/etc/init.d/snmpd restart

And type the following command to check if you to retrieve the SNMP values:
snmpwalk -v 1 -c public localhost system

Now we're ready to use MRTG. First generate the config file with the command:

cfgmaker 127.0.0.1 --output test.cfg

Edit the generated file "test.cfg" and check the WorkDir setting, it should be already set. If not, do it:
WorkDir: /var/www/mrtg

A few line later, it should contqin an entry for each network interface MRTG has found querying SNMP.

Then add the folowing settings:

Refresh: 300
Interval: 5
logformat: rrdtool
RunAsDaemon: Yes

Refresh is to tell the browser to refresh every 300 seconds.
Interval , in minutes, the interval to query
logformat :rrdtool tells mrtg to save data in rrdtool database
RunAsDaemon : so the process runs as a service

Then start mrtg, by typing as root

mrtg test.cfg

If everything is ok, you will get

Daemonizing MRTG ...

Check now in /var/www/mrtg, you should have a rrdtool database file. It is name with the IP address and the network interface. In my case:
127.0.0.1_3.rrd

type to see the content:
rrdtool info 127.0.0.1_3.rrd

It should display something like:

ds[ds0].type = "COUNTER"
ds[ds0].minimal_heartbeat = 600
ds[ds0].min = 0.0000000000e+00
ds[ds0].max = 1.2500000000e+06
ds[ds0].last_ds = "14331604"
ds[ds0].value = 1.2166000000e+03

At least, setup 14all to generate the graphics.
Download it from http://my14all.sourceforge.net/
Choose to download : 14all.cgi v1.1p25

Rename the file with an extension .cgi and place it in the Apache cgi-bin directory :
/var/www/cgi-bin together with the MRTG config file.

In your browser:
http://localhost/cgi-bin/14all.cgi?cfg=test.cfg

You should see a page with graphs showing the traffic analysis of your network interface.
Here I am surfing for one hour on internet:


As an alternative to 14all, you may also check router2cgi
It works exactly the same but it is richer.