Chitt Ranjan Mahto (Chirag)

Posted on Aug 3

How To Install Nagios on Ubuntu 24.04 LTS and also add Remote Host

        Chirag's Technology Tutorial

How To Install Nagios on Ubuntu 24.04 LTS and also add Remote Host

Here's a step-by-step guide to install Nagios Core (latest stable version) on Ubuntu 24.04 LTS, including Apache setup, dependencies, user configuration, and starting the Nagios web interface.

Nagios Server IP : 192.168.224.128
Part - I - Configure Nagios

Step 1: Update System

sudo apt update && sudo apt upgrade -y
Step 2: Install Required Dependencies

sudo apt install -y autoconf gcc libperl-dev make apache2 php php-gd libgd-dev \
libapache2-mod-php libssl-dev daemon unzip wget libtool libxml2-dev \
libjansson-dev libdbi-dev libsqlite3-dev
Step 3: Create Nagios User and Group

sudo useradd nagios
sudo groupadd nagcmd
sudo usermod -aG nagcmd nagios
sudo usermod -aG nagcmd www-data
Step 4: Download and Install Nagios Core

Download Latest Nagios (Update URL if needed)

cd /tmp

wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.5.9.tar.gz

tar -xzf nagios-4.5.9.tar.gz

cd nagios-4.5.9

Compile and Install:

./configure --with-command-group=nagcmd

make all

sudo make install

sudo make install-commandmode

sudo make install-init

sudo make install-config

sudo make install-webconf
Step 5: Set up Web Access

Create Nagios Admin User:

sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
Enter a password (e.g., admin@123)

Step 6: Install and Configure Nagios Plugins

cd /tmp

wget https://nagios-plugins.org/download/nagios-plugins-2.4.9.tar.gz

tar -xzf nagios-plugins-2.4.9.tar.gz

cd nagios-plugins-2.4.9

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

make

sudo make install
Step 7: Enable and Start Nagios and Apache

sudo systemctl enable apache2

sudo systemctl enable nagios

sudo systemctl start apache2

sudo systemctl start nagios
Step 8: Allow Firewall (if UFW enabled)

sudo ufw allow Apache
sudo ufw reload
Step 9: Enable CGI Module (Required by Nagios)

sudo a2enmod cgi

systemctl restart apache2
Step 10: Access Nagios Web UI

Open your browser and go to:

http://192.168.224.128/nagios
Login:

Username: nagiosadmin
Password: The one you set (e.g., admin@123)

Optional: Verify Nagios Configuration

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

Total Warnings: 0

Total Errors: 0

Part - II Configure the Nagios Server (192.168.224.128) to Monitor Remote Hosts

Step 1: After adding the NRPE service to a remote host, you should also make some changes to the Nagios server to allow the server to communicate to the remote host. Follow the steps below to configure the Nagios server.

Ensure you're connected to the Nagios server through SSH.

Create a new servers directory on Negios Server (192.168.224.128).

sudo mkdir -p /usr/local/nagios/etc/servers/
Step 2: Create a new /usr/local/nagios/etc/servers/host.cfg configuration file to store remote hosts' information.

sudo nano /usr/local/nagios/etc/servers/host.cfg
Add the following configurations to the file. Replace Vultr with your remote hostname and remote-host-ip with the remote host's public IP address.

define host {
use linux-server
host_name RemoteHost #your host name
alias My Remote Host #Alias Name
address 192.168.224.129 #IP Address of the remote host
max_check_attempts 5
check_period 24x7
notification_interval 30
notification_period 24x7
}
Save and close the file.

In the above configuration:

max_check_attempts: Sets the maximum number of retries before marking the host as down.

check_period: Sets the period to perform host checks.

notification_interval: Sets the interval (in minutes) between consecutive notifications.

notification_period: Sets the period to send notifications in the Nagios dashboard.

Step 3: Open the main Nagios (192.168.224.128) configuration file to enable the remote host configuration.

sudo nano /usr/local/nagios/etc/nagios.cfg
Add the following directive at the end of the file.

cfg_dir=/usr/local/nagios/etc/servers
Save and close the file.

Step 4: Restart the Nagios service to apply the configuration changes.

sudo systemctl restart nagios
Step 5: Test the Nagios configuration for errors.

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

Total Warnings: 0

Total Errors: 0

Things look okay - No serious problems were detected during the pre-flight check

Restart Nagios to apply the configuration changes.

sudo systemctl restart nagios

Access the Nagios web monitoring dashboard.

http://192.168.224.128/nagios
🖥 On Remote Host

Install NRPE and Plugins

Ubuntu/Debian:

sudo apt update && sudo apt install nagios-nrpe-server nagios-plugins -y
CentOS/RHEL:

sudo yum install epel-release -y
sudo yum install nrpe nagios-plugins-all -y

Edit NRPE Configuration

sudo nano /etc/nagios/nrpe.cfg
Set allowed_hosts to include the IP of your Nagios server:

allowed_hosts=127.0.0.1,192.168.224.128 ; Replace with your Nagios server IP

Start and Enable NRPE

sudo systemctl restart nagios-nrpe-server
sudo systemctl enable nagios-nrpe-server
🔁 Final Steps on Nagios Server (192.168.224.128)

Check Nagios Config and Restart

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

Access Nagios Web Interface

Go to: http://192.168.224.128/nagios
Login and check the remote host and services status.

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How To Install Nagios on Ubuntu 24.04 LTS and also add Remote Host

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