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Monitoring Servers with Munin on Ubuntu 11.04 (Natty)

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The Linode Manager provides some basic monitoring of system resource utilization, which includes information regarding Network, CPU, and Input/Output usage over the last 24 hours and 30 days. While this basic information is helpful for monitoring your system, there are cases where more fine-grained information is useful. For instance, if you need to monitor memory usage or resource consumption on a per-process level, a more precise monitoring tool like Munin might be helpful.

Munin is a system and network monitoring tool that uses RRDTool to generate useful visualizations of resource usage. The primary goal of the Munin project is to provide an easy to use tool that is simple to install and configure and provides information in an accessible web based interface. Munin also makes it possible to monitor multiple “nodes” with a single installation.

Before installing Munin, we assume that you have followed our getting started guide. If you are new to Linux server administration, you may be interested in our introduction to Linux concepts guide, beginner’s guide and administration basics guide. Additionally, you’ll need to install a web server such as Apache in order to use the web interface.

Installing Munin

Make sure your package repositories and installed programs are up to date by issuing the following commands:

apt-get update
apt-get upgrade --show-upgraded

The Munin system has two components: a master component often referred to as simply “munin,” and a “node” component, or “munin-node,” which collects the data and forwards it to the master node. In Lucid, you need to install both the munin and munin-node packages if you wish to monitor the Linode you plan to use as the primary Munin device. To install these packages, issue the following command:

apt-get install munin munin-node

On all of the additional machines you administer that you would like to monitor with Munin, issue the following command:

apt-get install munin-node

The machines that you wish to monitor with Munin do not need to run Ubuntu. The Munin project supports monitoring for a large number of operating systems. Consult the Munin project’s installation guide for more information installing nodes on additional operating systems.

Configuring Munin

Munin Master Configuration

The master configuration file for Munin is /etc/munin/munin.conf. This file is used to set the global directives used by Munin, as well as the hosts monitored by Munin. This file is large, so we’ve opted to show the key parts of the file. For the most part, the default configuration will be suitable to your needs.

The first section of the file contains the paths to the directories used by Munin. Note that these directories are the default paths used by Munin and can be changed by uncommenting and updating the path. When configuring your web server with Munin, make sure to point the root folder to the path of htmldir.

/etc/munin/munin.conf 
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<VirtualHost 12.34.56.78:80>
   ServerAdmin webmaster@stats.example.org
   ServerName stats.example.org
   DocumentRoot /var/cache/munin/www
   <Directory />
       Options FollowSymLinks
       AllowOverride None
   </Directory>
   LogLevel notice
   CustomLog /var/log/apache2/access.log combined
   ErrorLog /var/log/apache2/error.log
   ServerSignature On
</VirtualHost>

# dbdir /var/lib/munin # htmldir /var/cache/munin/www # logdir /var/log/munin # rundir /var/run/munin

There are additional directives after the directory location block such as tmpldir, which shows Munin where to look for HTML templates, and others that allow you to configure mail to be sent when something on the server changes. These additional directives are explained more in depth on the munin.conf page of the Munin website. You can also find quick explanations inside the file itself via hash (#) comments. Take note that these global directives must be defined prior to defining hosts monitored by Munin. Do not place global directives at the bottom of the munin.conf file.

The last section of the munin.conf file defines the hosts Munin retrieves information from. For a default configuration, adding a host can be done in the form shown below:

/etc/munin/munin.conf 
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[example.org]
:   address example.org

For more complex configurations, including grouping domains, see the comment section in the file, reproduced below for your convenience:

/etc/munin/munin.conf 
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\# A more complex example of a host tree \# \#\# First our "normal" host. \# [fii.foo.com] \# address foo \# \#\# Then our other host... \# [fay.foo.com] \# address fay \# \#\# Then we want totals... \# [foo.com;Totals] \#Force it into the "foo.com"-domain... \# update no \# Turn off data-fetching for this "host". \# \# \# The graph "load1". We want to see the loads of both machines... \# \# "fii=fii.foo.com:load.load" means "label=machine:graph.field" \# load1.graph\_title Loads side by side \# load1.graph\_order fii=fii.foo.com:load.load fay=fay.foo.com:load.load \# \# \# The graph "load2". Now we want them stacked on top of each other. \# load2.graph\_title Loads on top of each other \# load2.dummy\_field.stack fii=fii.foo.com:load.load fay=fay.foo.com:load.l\$ \# load2.dummy\_field.draw AREA \# We want area instead the default LINE2. \# load2.dummy\_field.label dummy \# This is needed. Silly, really. \# \# \# The graph "load3". Now we want them summarized into one field \# load3.graph\_title Loads summarized \# load3.combined\_loads.sum fii.foo.com:load.load fay.foo.com:load.load \# load3.combined\_loads.label Combined loads \# Must be set, as this is \# \# not a dummy field! \# \#\# ...and on a side note, I want them listen in another order (default is \#\# alphabetically) \# \# \# Since [foo.com] would be interpreted as a host in the domain "com", we \# \# specify that this is a domain by adding a semicolon. \# [foo.com;] \# node\_order Totals fii.foo.com fay.foo.com \#

Munin Node Configuration

The default /etc/munin/munin-node.conf file contains several variables you’ll want to adjust to your preference. For a basic configuration, you’ll only need to add the IP address of the master Munin server as a regular expression. Simply follow the style of the existing allow line if you’re unfamiliar with regular expressions.

/etc/munin/munin-node.conf 
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\# A list of addresses that are allowed to connect. This must be a \# regular expression, due to brain damage in Net::Server, which \# doesn't understand CIDR-style network notation. You may repeat \# the allow line as many times as you'd like

allow \^127.0.0.1\$

\# Replace this with the master munin server IP address allow \^123.45.67.89\$

The above line tells the munin-node that the master Munin server is located at IP address 123.45.67.89. After updating this file, restart the munin-node. In Ubuntu, use the following command:

/etc/init.d/munin-node restart

Web Interface Configuration

You can use Munin with the web server of your choice, simply point your web server to provide access to resources created by Munin. By default, these resources are located at /var/cache/munin/www.

If you are using the Apache HTTP Server you can create a Virtual Host configuration to serve the reports from Munin. In this scenario, we’ve created a subdomain in the DNS Manager and are now creating the virtual host file:

/etc/apache2/sites-available/stats.example.org 
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<VirtualHost 12.34.56.78:80>
   ServerAdmin webmaster@stats.example.org
   ServerName stats.example.org
   DocumentRoot /var/cache/munin/www
   <Directory />
       Options FollowSymLinks
       AllowOverride None
   </Directory>
   LogLevel notice
   CustomLog /var/log/apache2/access.log combined
   ErrorLog /var/log/apache2/error.log
   ServerSignature On
</VirtualHost>

If you use this configuration you will want to issue the following commands to ensure that all required directories exist, and that your site is enabled:

a2ensite stats.example.org

Now restart the server so that the changes to your configuration file can take effect. Issue the following command:

/etc/init.d/apache2 restart
/etc/init.d/apache2 reload

In most cases you will probably want to prevent the data generated by Munin from becoming publicly accessible. You can either limit access using rule based access control so that only a specified list of IPs will be permitted access, or you can configure HTTP Authentication to require a password before permitting access.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

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