Introduction

Munin is a system, network, and infrastructure monitoring application that provides information in graphs through a web browser. It is designed around a client-server architecture and can be configured to monitor the machine it's installed on (the Munin master) and any number of client machines, which in Munin parlance, are called Munin nodes.

In this article, we'll install and configure Munin to monitor the server it's installed on and one node. To install Munin on multiple nodes, just follow the instructions for creating a node on each system.

Prerequisites

• Two Debian 8.1 Droplets
• For each Droplet, a non-root user with sudo privileges

Except otherwise noted, all of the commands in this tutorial should be run as a non-root user with sudo privileges. To learn how to create users and grant them sudo privileges, check out Initial Server Setup with Debian 8.

Step 1 — Installing Required Packages

We will start working on the Munin master first. Before installing Munin, a few dependencies need to be installed.

Though Munin can function with most popular Web servers like Nginx and Lighttpd, it is, by default, designed to work with the Apache Web server. So be sure that Apache is installed and configured on the Munin master. If it's not already installed, do so using:

sudo apt-get update
sudo apt-get install -y apache2

• To ensure that the dynazoom functionality responsible for zooming into the generated graphs works properly on click, install the following:

sudo apt-get install -y libcgi-fast-perl libapache2-mod-fcgid

After installing those two packages, the fcgid module should have been enabled. To double-check, type:

/usr/sbin/apachectl -M | grep -i cgi

The output should be:

fcgid_module (shared)

If the output is blank, then it is not enabled. You may then enable it using:

sudo a2enmod fcgid

When executing the apachectl command, you can ignore the following warning:

Could not reliably determine the server's fully qualified domain name ...

Apache will still work with Munin with this warning.

The rest of the configuration that will make graph zooming work properly will be covered in Step 3.

Step 2 — Installing Munin on the Munin Master

Installation packages for Munin are available in the Debian repository, so it can be installed using the distribution's package manager. In this step, you'll install the Munin master package from the stable branch. The version in the Debian repository, Munin 2.0.25, is the same as the latest stable release.

To install it, type:

sudo apt-get install -y munin

Step 3 — Configuring the Munin Master

The Munin master's main configuration file munin.conf and other files required for it to function can be found in the /etc/munin directory and its sub-directories.

The configuration file is made up of at least two sections — a global and at least one host section. Optionally, there can be a group section. Host and group sections start with their respective names in square brackets. This file contains variable definitions, directives that govern how Munin monitors servers and services, and which servers to monitor.

To start modifying it:

cd /etc/munin
sudo nano munin.conf

Look for these lines and uncomment them. That is, remove the # sign that precedes them. The dbdir stores all of the rrdfiles containing the actual monitoring information; htmldir stores the images and site files; logdir maintains the logs; rundir holds the state files; and tmpldir is the location for the HTML templates. Be sure to change the htmldir from /var/cache/munin/www to your web directory. In this example, we'll be using /var/www/munin:

dbdir     /var/lib/munin
htmldir   /var/www/munin
logdir    /var/log/munin
rundir    /var/run/munin
...
tmpldir /etc/munin/templates

Since the htmldir does not exist, let's create and chown it so that it's owned by the munin system user:

sudo mkdir /var/www/munin
sudo chown munin:munin /var/www/munin

Finally, look for the first host tree in munin.conf. It should read:

[localhost.localdomain]
    address 127.0.0.1
    use_node_name yes

Change the name of that tree to one that uniquely identifies the server. In this example, we'll be using MuninMaster:

[MuninMaster]
    address 127.0.0.1
    use_node_name yes

That's all for the configuration file, so save and close it.

Within the same /etc/munin directory, the next file we'll be modifying is apache24.conf, which is Munin's Apache 2.4 configuration file. It is sym-linked to /etc/apache2/conf-available/munin.conf. To start modifying it, open it with nano:

sudo nano apache24.conf

At the very top of the file, modify the first line so that it reflects the htmldir path you specified in munin.conf and created previously. Based on the directory path used in this article, it should read as follows, which makes it so you can access Munin's web interface by appending munin to the server's IP address or domain hosted on the server:

Alias /munin /var/www/munin

To ensure that you can access Munin's web interface remotely, delete the directory section and replace it with this:

<Directory /var/www/munin>
        Require all granted
        Options FollowSymLinks SymLinksIfOwnerMatch
</Directory>

Do the same with the last location section. Remove the Require local line and replace it with the following:

<Location /munin-cgi/munin-cgi-graph>
        Require all granted
        Options FollowSymLinks SymLinksIfOwnerMatch
        ...
</Location>

Save and close the file. Then restart Munin and Apache:

sudo systemctl restart munin-node
sudo systemctl restart apache2

You may now access Munin's web interface by pointing your Web browser to server-ip-address/munin

Step 4 — Adding a Node to Munin Master

In this step, we'll show how to add a node to the Munin master. This involves modifying the Munin master's configuration file to specify a host tree for the node, installing the Munin node package on the node, and modifying its configuration file so that it can be monitored by the Munin master.

Let's start with the Munin node — the other Debian 8 Droplet you created.

Log into the Munin node, update the package database, and install the Munin node package:

sudo apt-get update
sudo apt-get install -y munin-node

After the installation has completed successfully, the node's configuration should be in the /etc/munin directory. Open it with nano:

sudo nano /etc/munin/munin-node.conf

Towards the middle of the file, look for an allow ^127.0.0.1$ line and modify it so that it reflects the IP address of the Munin master. Note that the IP address is in regex format, so assuming that the master server IP address is 123.46.78.100, the line should read:

allow ^123\.456\.78\.100$

Save and close the file. Then restart the Munin:

sudo systemctl restart munin-node

Back on the Munin master, open the main configuration file:

sudo nano /etc/munin/munin.conf

All we need to do in this file is insert a host tree for the (remote) node. The easiest approach to that is to copy and modify the host tree of the master. Be sure to replace node-ip-address with the IP address of the node you are adding:

[MuninNode]
    address node-ip-address
    use_node_name yes

Save and close the file. Then restart Apache:

sudo systemctl restart apache2

Munin checks for new nodes every 5 minutes. Wait a few minutes, then reload the Munin master's web interface. You should see an entry for the node. If you don't see it yet, try again in 5 minutes. Using this method, you may add as many nodes as you have to monitor.

Step 5 — Enabling Extra Plugins

Munin monitors a system using plugin scripts, and by default, about a dozen set of plugins are installed and active. A complete list of available plugins are in the /usr/share/munin/plugins directory. To see which plugins can be used on your system, Munin provides the following command:

sudo munin-node-configure --suggest

The output should be of this sort:

Plugin                     | Used | Suggestions
------                     | ---- | -----------
cps_                       | no   | no
cpu                        | yes  | yes
cpuspeed                   | no   | no [missing /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state]
cupsys_pages               | no   | no [could not find logdir]
df                         | yes  | yes
df_inode                   | yes  | yes
fail2ban                   | no   | yes
ip_                        | no   | yes

A plugin with a yes in the Used column means just what it indicates, while one with a yes in the Suggestions column means it can be used. One with a no on both columns means it is not in use and cannot be used on the system. Finally, if a plugin has a no in the Used column and a yes in the Suggestions, then it is not being used but can be enabled and used on the system.

On the Munin master and node, you can also see a list of installed plugins in the /etc/munin/plugins directory.

A munin-plugins-extra package should have been installed when you installed Munin. If it was not, do so using.

sudo apt-get install munin-plugins-extra

To enable an available plugin that's not currently in use, create a symbolic link for it from the /usr/share/munin/plugins directory to the /etc/munin/plugin directory.

For example, to enable the Fail2ban plugin, first install Fail2ban:

sudo apt-get install fail2ban

Then, create the symlink that enables the Munin plugin:

sudo ln -s /usr/share/munin/plugins/fail2ban /etc/munin/plugins

Restart Munin:

sudo systemctl restart munin-node

Wait a few minutes, reload the web interface, and you should see graphs for Fail2ban under the title Hosts blacklisted by fail2ban under the network category for the Munin master.

Troubleshooting

If you are having trouble configuring the Munin master, the Munin node, or getting the master to see the node, check out the log files for error messages:

• Munin master: /var/log/munin/munin-update.log
• Munin node: /var/log/munin/munin-node.log

You can also check the project's page for additional troubleshooting tips.

Conclusion

Munin can be configured to monitor the system on which it is installed. Adding remote servers to the monitored system is as simple as install the munin-node package on the remote server (or node) and then modifying the server's and node's configuration files to point to the other IP address.

Munin works by using plugins, but not all are enabled out of the box. Information about plugins are available on the project's page.