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Nagios installation in Ubuntu 20.04

Prerequisites

  • Deploy a fully updated Ubuntu 20.04 Server.
  • Create a non-root user with sudo access.

1. Install and Configure Nagios Core

  1. Update the system packages.

    sudo apt update

  2. Install all the required packages.

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

  3. Download Nagios Core Setup files. To download the latest version, visit the official releases site.

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

  4. Extract the downloaded files.

    sudo tar -zxvf nagios-4.4.6.tar.gz

  5. Navigate to the setup directory.

    cd nagios-4.4.6

  6. Run the Nagios Core configure script.

    sudo ./configure

  7. Compile the main program and CGIs.

    sudo make all

  8. Make and install group and user.

    sudo make install-groups-users

  9. Add www-data directories user to the nagios group.

    sudo usermod -a -G nagios www-data

  10. Install Nagios.

    sudo make install

  11. Initialize all the installation configuration scripts.

    sudo make install-init

  12. Install and configure permissions on the configs' directory.

    sudo make install-commandmode

  13. Install sample config files.

    sudo make install-config

  14. Install apache files.

    sudo make install-webconf

  15. Enable apache rewrite mode.

    sudo a2enmod rewrite

  16. Enable CGI config.

    sudo a2enmod cgi

  17. Restart the Apache service.

    sudo systemctl restart apache2

  18. Create a user and set the password when prompted.

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

  19. provide access to 'admin' user to monitor the hosts and services

    sudo vi /usr/local/nagios/etc/cgi.cfg

NOTE: For bulk replace in vi enter as below :%s/nagiosadmin/nagiosadmin,admin/gi and save the file

2. Install Nagios Plugins

  1. Download the Nagios Core plugin. To download the latest plugins, visit the plugins download page.

    cd ~/

    wget https://nagios-plugins.org/download/nagios-plugins-2.3.3.tar.gz

  2. Extract the downloaded plugin.

    sudo tar -zxvf nagios-plugins-2.3.3.tar.gz

  3. Navigate to the plugins' directory.

    cd nagios-plugins-2.3.3/

  4. Run the plugin configure script.

    sudo ./configure --with-nagios-user=nagios --with-nagios-group=nagios

  5. Compile Nagios Core plugins.

    sudo make

  6. Install the plugins.

    sudo make install

  7. Add / uncomment below to nagios.cgi file.

    sudo nano /usr/local/nagios/etc/nagios.cfg

    cfg_dir=/usr/local/nagios/etc/services

    Save the file

3. Verify Nagios Configuration

  1. Verify the Nagios Core configuration.

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

  2. Start the Nagios service.

    sudo systemctl start nagios

  3. Enable Nagios service to run at system startup.

    sudo systemctl enable nagios

4. Access Nagios Web Interface

Open your web browser and access Nagios web interface via the URL http://ServerIP/nagios. For my case:

http://192.168.122.162/nagios

You have successfully installed Nagios Core on your server. To log in, use admin as your username and the password you set during the user account creation step as your password. You can now access the dashboard and begin configuring Nagios.

5. Add Remote Hosts

To monitor hosts, we need to add them to Nagios. By default, Nagios only monitors localhost (the server it's running on). We're going to add hosts that are part of our network to gain even more control. You will need to use the following instructions on all hosts that you want to monitor.

First, install nagios-plugins and nagios-nrpe-server:

sudo apt-get install nagios-plugins nagios-nrpe-server

Configure NRPE

open the /etc/nagios/nrpe.cfg file. Replace the value of allowed_hosts with 127.0.0.1,nagios_server_IP and server_address with 0.0.0.0

Save the file when you are finished.

restart NRPE:

sudo systemctl restart nagios-nrpe-server or service nagios-nrpe-server restart

Add the Host to Nagios ( In nagios server )

  1. Create folder and file /usr/local/nagios/etc/servers/host.cfg and update file as below

    sudo mkdir -p /usr/local/nagios/etc/servers/

    sudo nano /usr/local/nagios/etc/servers/host.cfg

    Use the following block as a template. Replace host with an appropriate name for your remote host, and update the host_name, alias, and address values accordingly.

      define host {
        use                             linux-server
        host_name                       nagios-cli1
        alias                           My first Apache server
        address                         192.168.122.145
        max_check_attempts              5
        check_period                    24x7
        notification_interval           30
        notification_period             24x7
}

    save the file

  2. Uncomment following in /usr/local/nagios/etc/nagios.cfg file.

    Open file

    sudo nano /usr/local/nagios/etc/nagios.cfg

    Uncomment below and save the file

    cfg_file=/usr/local/nagios/etc/services.cfg

  3. Verify nagios configuration files syntax

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

  4. restart or reload the nagios servie

    sudo systemctl restart nagios or sudo systemctl reload nagios

Open your web browser and access Nagios web interface via the URL http://ServerIP/nagios. For my case:

http://192.168.122.162/nagios

To monitor and report a remote host USB, you can refer to the guide on configuring USB checks in Nagios for Ubuntu. You can find it at USB.