14.5. Configuring and Starting MRTG on Debian

Problem

OK already, enough with the preliminaries. Your SNMP and HTTP daemons are installed and running, and you want to get going with MRTG and start making nice network graphs like everyone else. What do you do now?

Solution

First, we'll have MRTG monitor all the up network interfaces on our server.

Run this command to create the initial MRTG configuration file. password is whatever SNMP community string you set:

	# cfgmaker --output=/etc/mrtg.cfg \
	--global "workdir: /var/www/mrtg" -ifref=ip \
	--global 'options[_]: growright,bits' \
	password@localhost

Then, start it manually:

	# mrtg /etc/mrtg.conf
	-----------------------------------------------------------------------
	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 /etc/mrtg.cfg
	-----------------------------------------------------------------------

So, do that:

	# env LANG=C mrtg /etc/mrtg.cfg

If your default is already LANG=C, then you won't see that message. If you get "Rateup WARNING" error messages, repeat the command until they go away. This usually takes three tries.

Run this command to create the HTML index file:

	# indexmaker --output=/var/www/mrtg/index.html /etc/mrtg.cfg

Now, point a web browser to localhost (http://localhost/mrtg/), and you should see nice graphs tracking all of your up interfaces, like in Figure 14-2.

MRTG graphs of two active local network interfaces

Figure 14-2. MRTG graphs of two active local network interfaces

Click on any graph to view detailed statistics, as shown in Figure 14-3.

This shows that it is working correctly.

Discussion

Let's take a look at what we did in the command:

--output=/etc/mrtg.cfg

This tells the cfgmaker command where to create the MRTG configuration file.

--global"workdir:/var/www/mrtg"-ifref=ip

This setting goes in the global section of mrtg.cfg, and defines the directory where the HTML files are stored. -ifref=ip tells MRTG to track your network interfaces by IP address.

--global'options[_]:growright,bits'

This means your graphs will expand to the right, and network traffic will be measured in bits.

password@localhost

The community string (password) for snmpd.

Debian installs a crontab for MRTG in /etc/cron.d/mrtg that updates the graphs every five minutes, so you don't need to take any additional steps to keep it running.

Running env LANG=Cmrtg/etc/mrtg.cfg commonly emits error messages like this:

	Rateup WARNING: /usr/bin/rateup could not read the primary log file for localhost_
	192.168.1.10
	Rateup WARNING: /usr/bin/rateup The backup log file for localhost_192.168.1.10 was
	invalid as well
	Rateup WARNING: /usr/bin/rateup Can't remove localhost_192.168.1.10.old updating log
	file
	Rateup WARNING: /usr/bin/rateup Can't rename localhost_192.168.1.10.log to localhost_
	192.168.1.10.old updating log file
Detailed interface statistics

Figure 14-3. Detailed interface statistics

It's just complaining about routine business. Ignore it, and keep running the command until it doesn't emit any more error messages; three times usually does the job.

See Also