install and configure nagios

What is Nagios?

• Nagios is an open-source monitoring system that helps track the health, availability, and performance of networked systems.
• It alerts administrators when issues arise and provides insights to prevent potential failures.

Why We Use It?

• Monitors web server uptime and response times.
• Tracks database performance and alerts on high query load.
• Sends email/SMS alerts when an API fails, ensuring minimal downtime.
• Generates reports on system performance for capacity planning.

This document provides a step-by-step guide to configuring a Nagios server, covering the following tasks:

• Setting up Nagios on the master server
• Installing and configuring the Nagios client on a remote server
• Adding the Nagios client to the master server
• Creating and integrating custom Nagios plugins or services using shell scripts
• Enabling email notifications for alerts

📝 Installing Nagios on Master Server 📝

Step 1: Update System

• sudo apt update -y

Step 2: Install Required Dependencies

sudo apt install -y apache2 nagios-nrpe-plugin php php-gd libgd-dev unzip build-essential  libapache2-mod-php libperl-dev libssl-dev daemon wget

Step 3: Create Nagios User & Group

• sudo useradd nagios && sudo groupadd nagios && sudo usermod -aG nagios www-data

Step 4: Download & Install Nagios Core

cd /usr/src wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.5.1.tar.gz tar -xvzf nagios-4.5.1.tar.gz cd nagios-4.5.1 sudo ./configure --with-httpd-conf=/etc/apache2/sites-enabled sudo make all sudo make install sudo make install-init sudo make install-commandmode sudo make install-config sudo make install-webconf

Step 5: Set Up Apache & Firewall

• sudo a2enmod rewrite cgi
• sudo systemctl restart apache2

Step 6: Install Nagios Plugins

cd /usr/src wget https://nagios-plugins.org/download/nagios-plugins-2.4.7.tar.gz tar -xvzf nagios-plugins-2.4.7.tar.gz cd nagios-plugins-2.4.7 sudo ./configure sudo make sudo make install

Step 7: Create Admin User for Web Access

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

Step 8: Enable & Start Nagios

• sudo systemctl enable nagios
• sudo systemctl start nagios

Step 9: Access Nagios Web Interface

• http://<server-ip>/nagios

📝 Installing Nagios Client (NRPE) on Remote Server 📝

Step 1: Update System

• sudo apt update -y

Step 2: Install NRPE and Nagios Plugins

• sudo apt install -y nagios-nrpe-server nagios-plugins

Step 3: Configure NRPE

• sudo nano /etc/nagios/nrpe.cfg

Find the following line and update with Nagios Server IP

• allowed_hosts=100.100.7.226

Step 4: Restart NRPE Service

• sudo systemctl restart nagios-nrpe-server
• sudo systemctl enable nagios-nrpe-server

📝 Add Client Remote Host in Nagios Server 📝

Step 1: Test NRPE Connection from "Nagios Server"

• /usr/lib/nagios/plugins/check_nrpe -H <nagios-client-ip>

Step 2: Add Client to Nagios Server 

• sudo mkdir /usr/local/nagios/etc/servers/
• sudo vim /usr/local/nagios/etc/servers/client.cfg

define host { use linux-server host_name Client1 address <nagios-client-ip> check_command check-host-alive max_check_attempts 5 notification_interval 30 notification_period 24x7 }

Step 3: Edit Nagios Conf file and add below line at the end.

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

• cfg_dir=/usr/local/nagios/etc/servers

Step 4: Check Status 

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

Step 5: Restart Nagios on Server

• sudo systemctl restart nagios

Step 6: Access Nagios Web Interface

• http://<server-ip>/nagios

📝 Add Nagios Custom Plugin or Services by Shell Script 📝

Step 1: Create a Custom Nagios Plugin

• sudo vim /usr/local/nagios/libexec/check_disk_usage.sh

#!/bin/bash DISK_USAGE=$(df / | awk 'NR==2 {print $5}' | sed 's/%//') if [ "$DISK_USAGE" -lt 80 ]; then echo "OK - Disk usage is $DISK_USAGE%" exit 0 elif [ "$DISK_USAGE" -lt 90 ]; then echo "WARNING - Disk usage is $DISK_USAGE%" exit 1 else echo "CRITICAL - Disk usage is $DISK_USAGE%" exit 2 fi

• chmod +x /usr/local/nagios/libexec/check_disk_usage.sh

Step 2: Edit the NRPE configuration file and add below line at bottom.

sudo vim /etc/nagios/nrpe.cfg

• command[check_disk_usage]=/usr/lib/nagios/plugins/check_disk_usage.sh

Step 3: Edit the Nagios command configuration file and add below line at bottom.

• sudo vim /usr/local/nagios/etc/objects/commands.cfg

define command { command_name check_disk_usage command_line /usr/local/nagios/libexec/check_disk_usage.sh }

Step 4: Restart NRPE on the client.

• sudo systemctl restart nagios-nrpe-server

Step 5: Define Monitoring Service nagios master server.

• sudo vim /usr/local/nagios/etc/servers/client.cfg

define service { use generic-service host_name client1 service_description Disk Usage check_command check_nrpe!check_disk_usage }