How to Install Nagios on Ubuntu 20.04

Nagios is an open-source monitoring tool that allows you to monitor the status and health of various systems, applications, and services. It helps you to identify and resolve issues before they impact your infrastructure and users.

Here is a step-by-step guide to install Nagios on Ubuntu 20.04:

1. Install necessary dependencies:

   sudo apt-get update
   sudo apt-get install -y build-essential apache2 php libapache2-mod-php php-gd libgd-dev sendmail unzip

2. Download Nagios Core:

   cd /tmp
   wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.6.tar.gz

3. Extract the archive and navigate to the extracted folder:

   tar -zxvf nagios-4.4.6.tar.gz
   cd nagios-4.4.6

4. Compile and install Nagios:

   ./configure --with-httpd-conf=/etc/apache2/sites-enabled
   make all
   sudo make install
   sudo make install-init
   sudo make install-commandmode
   sudo make install-config

5. Create a new nagiosadmin user account:

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

6. Download and install Nagios Plugins:

   cd /tmp
   wget https://nagios-plugins.org/download/nagios-plugins-2.3.3.tar.gz
   tar -zxvf nagios-plugins-2.3.3.tar.gz
   cd nagios-plugins-2.3.3
   ./configure --with-nagios-user=nagios --with-nagios-group=nagios
   make
   sudo make install

7. Configure Apache for Nagios web interface:

   sudo ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/
   sudo systemctl restart apache2

8. Verify the Nagios configuration:

   sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

9. Start Nagios service:

   sudo systemctl enable --now nagios

You can now access your Nagios installation by opening a web browser and navigating to http://YOUR_SERVER_IP/nagios. Login using the nagiosadmin account that you created earlier.