How to Install Nagios 4 on Ubuntu 18.04 & 16.04 LTS

Nagios is the most popular, open source, powerful monitoring system for any kind of infrastructure. It enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes. Nagios has the capability of monitoring application, services, entire IT infrastructure.

This article will help you to setup Nagios Monitoring Server on Ubuntu 18.04 LTS, 16.04 LTS, and 14.04 LTS and Debian systems. After completing this article, you will like to follow below tutorials.

How to Monitor remote Linux host using Nagios
How to Monitor remote Windows host using Nagios

Step 1 – Prerequisite

We assume that you have fresh installed Ubuntu/Debian systems, So our first requirement is to install Apache and PHP first. Use the following commands to complete it. You can find detailed LAMP setup instruction here.

Let’s use following commands to install required packages for Nagios.

sudo apt-get update
sudo apt-get install wget build-essential unzip openssl libssl-dev
sudo apt-get install apache2 php libapache2-mod-php php-gd libgd-dev 

2Step 2 – Create Nagios User

First of all, create a new user account for Nagios in your system and assign a password.

sudo adduser nagios

Now create a group for Nagios setup “nagcmd” and add nagios user to this group. Also, add nagios user in the Apache group.

sudo groupadd nagcmd
sudo usermod -a -G nagcmd nagios
sudo usermod -a -G nagcmd www-data

Step 3 – Install Nagios Core Service

After installing required dependencies and adding user accounts. Let’s start with Nagios core installation. Download latest Nagios core service from the official site.

cd /opt/
wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.3.tar.gz
tar xzf nagios-4.4.3.tar.gz

After extracting naviate to nagios source directory and install using make command.

cd nagios-4.4.3
sudo ./configure --with-command-group=nagcmd
sudo make all
sudo make install
sudo make install-init
sudo make install-daemoninit
sudo make install-config
sudo make install-commandmode
sudo make install-exfoliation

Now copy event handlers scripts under libexec directory. These binaries provides multiple events triggers for your Nagios web interface.

cp -R contrib/eventhandlers/ /usr/local/nagios/libexec/
chown -R nagios:nagios /usr/local/nagios/libexec/eventhandlers

Step 4 – Setup Apache with Authentication

Now create an Apache configuration file for your Nagios server as below:

sudo vi /etc/apache2/conf-available/nagios.conf

ScriptAlias /nagios/cgi-bin "/usr/local/nagios/sbin"

<Directory "/usr/local/nagios/sbin">
   Options ExecCGI
   AllowOverride None
   Order allow,deny
   Allow from all
   AuthName "Restricted Area"
   AuthType Basic
   AuthUserFile /usr/local/nagios/etc/htpasswd.users
   Require valid-user
</Directory>

Alias /nagios "/usr/local/nagios/share"

<Directory "/usr/local/nagios/share">
   Options None
   AllowOverride None
   Order allow,deny
   Allow from all
   AuthName "Restricted Area"
   AuthType Basic
   AuthUserFile /usr/local/nagios/etc/htpasswd.users
   Require valid-user
</Directory>

We need to setup apache authentication for user nagiosadmin. Until more specific reason use this username as “nagiosadmin” else you would require more changes in configuration.

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Now enable Apache configuration and restart Apache service to make the new settings take effect.

sudo a2enconf nagios
sudo a2enmod cgi rewrite
sudo service apache2 restart

Step 5 – Installing Nagios Plugins

After installing and configuring Nagios core service, Download latest nagios-plugins source and install using following commands.

cd /opt
wget http://www.nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz
tar xzf nagios-plugins-2.2.1.tar.gz
cd nagios-plugins-2.2.1

Now compile and install Nagios plugins

sudo ./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
sudo make
sudo make install

Step 6 – Verify Settings

Use the Nagios commands to verify the Nagios installation and configuration file. After successfully verify start the Nagios core service.

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
service nagios start

Also configure Nagios to auto start on system boot.

sudo systemctl enable nagios

Step 7 – Access Nagios Web Interface

Access your nagios setup by access nagios server using hostname or ip address followed by /nagios.
[change domain name with your domain or ip]

 http://svr1.tecadmin.net/nagios/

Prompting for Apache Authentication Password –

Nagios After login screen –

Finally, You have successfully installed and configured Nagios Monitoring Server core service in your system. Now visit net article to monitor Linux host and Windows host using Nagios server.