How To Install Nagios on AlmaLinux 9

In today’s complex IT environments, monitoring infrastructure is crucial for maintaining system health and preventing downtime. Nagios, a powerful open-source monitoring system, stands out as a reliable solution for tracking the status of network services, hosts, and servers. This guide will walk you through the process of installing Nagios on AlmaLinux 9, a robust enterprise-grade Linux distribution.

Nagios offers real-time alerts, performance tracking, and comprehensive reporting capabilities, making it an indispensable tool for system administrators and IT professionals. By following this step-by-step tutorial, you’ll be able to set up Nagios and start monitoring your IT infrastructure effectively.

Prerequisites

Before diving into the installation process, ensure you have the following:

• An AlmaLinux 9 server with root access or a non-root user with sudo privileges
• SELinux set to permissive mode (we’ll cover this in the guide)
• A stable internet connection for downloading packages
• Basic familiarity with Linux command-line operations

It’s crucial to have these prerequisites in place to ensure a smooth installation process. Let’s begin by preparing your AlmaLinux 9 system for Nagios.

Step 1: Update System Packages

Before installing any new software, it’s essential to update your system’s existing packages. This practice ensures compatibility and security. Open your terminal and run the following command:

sudo dnf update -y

This command updates all installed packages to their latest versions. The ‘-y’ flag automatically answers “yes” to any prompts, streamlining the update process.

Step 2: Install EPEL Repository

The Extra Packages for Enterprise Linux (EPEL) repository is a valuable resource for additional software packages not included in the default AlmaLinux repositories. Nagios and some of its dependencies are available through EPEL.

To install the EPEL repository, execute:

sudo dnf install epel-release

After installation, refresh your package cache:

sudo dnf makecache

This step ensures that your system is aware of the newly available packages from EPEL.

Step 3: Install Nagios Core

With the EPEL repository in place, we can now proceed to install Nagios Core and its essential components. Run the following command:

sudo dnf install nagios nagios-common nagios-plugins nagios-plugins-all nrpe

This command installs Nagios Core, common utilities, plugins, and NRPE (Nagios Remote Plugin Executor). The installation process may take a few minutes, depending on your internet speed and system performance.

During the installation, you might be prompted to confirm the installation of additional dependencies. Type ‘y’ and press Enter to proceed.

Step 4: Configure Nagios Core

After installation, it’s time to configure Nagios Core. This step involves setting up authentication, adjusting default settings, and verifying the web server configuration.

First, let’s set up a password for the Nagios web interface:

sudo htpasswd -c /etc/nagios/passwd nagiosadmin

You’ll be prompted to enter and confirm a password. Remember this password, as you’ll need it to access the Nagios web interface.

Next, we need to configure Apache to serve the Nagios web interface. Create a new configuration file:

sudo nano /etc/httpd/conf.d/nagios.conf

Add the following content to the file:

ScriptAlias /nagios/cgi-bin "/usr/lib64/nagios/cgi-bin"

<Directory "/usr/lib64/nagios/cgi-bin">
   Options ExecCGI
   AllowOverride None
   Require all granted
   <IfModule mod_authz_core.c>
      # Apache 2.4
      Require all granted
   </IfModule>
   <IfModule !mod_authz_core.c>
      # Apache 2.2
      Order allow,deny
      Allow from all
   </IfModule>
</Directory>

Alias /nagios "/usr/share/nagios/html"

<Directory "/usr/share/nagios/html">
   Options None
   AllowOverride None
   Require all granted
   <IfModule mod_authz_core.c>
      # Apache 2.4
      Require all granted
   </IfModule>
   <IfModule !mod_authz_core.c>
      # Apache 2.2
      Order allow,deny
      Allow from all
   </IfModule>
</Directory>

Save the file and exit the editor.

Now, restart Apache to apply the changes:

sudo systemctl restart httpd

Step 5: Start and Enable Nagios Service

With the configuration in place, it’s time to start the Nagios service and enable it to run at system boot:

sudo systemctl start nagios
sudo systemctl enable nagios

To verify that Nagios is running correctly, check its status:

sudo systemctl status nagios

You should see output indicating that Nagios is active and running.

Step 6: Install Nagios Plugins

Nagios plugins extend its functionality, allowing you to monitor a wide range of services and systems. While we installed some plugins earlier, you might want to add more based on your specific monitoring needs.

To browse available plugins, use:

sudo dnf search nagios-plugins

Install additional plugins as needed. For example, to install SNMP plugins:

sudo dnf install nagios-plugins-snmp

Remember to restart Nagios after installing new plugins:

sudo systemctl restart nagios

Step 7: Verify Installation

To ensure Nagios is installed correctly and running, perform these verification steps:

1. Check the Nagios service status:

sudo systemctl status nagios

Look for “Active: active (running)” in the output.

2. Verify Nagios configuration:

sudo /usr/sbin/nagios -v /etc/nagios/nagios.cfg

This command checks for configuration errors. If there are no errors, you’ll see “Total Warnings: 0” and “Total Errors: 0” at the end of the output.

3. Test Apache configuration:

sudo apachectl configtest

You should see “Syntax OK” if the configuration is correct.

If you encounter any issues during verification, review the previous steps and check the Nagios and Apache error logs for more information:

sudo tail -f /var/log/nagios/nagios.log
sudo tail -f /var/log/httpd/error_log

Accessing Nagios Web Interface

With Nagios installed and running, you can now access its web interface:

1. Open a web browser and navigate to:

http://your_server_ip/nagios

Replace “your_server_ip” with your AlmaLinux 9 server’s IP address or domain name.

2. You’ll be prompted for authentication. Use the username “nagiosadmin” and the password you set earlier.

3. Once logged in, you’ll see the Nagios dashboard. Take some time to explore the various sections:

• Tactical Overview: Provides a summary of your monitored services and hosts
• Map: Displays a visual representation of your network
• Services: Lists all monitored services and their current status
• Host Groups: Shows groups of monitored hosts
• Reports: Offers various reporting options for system status and performance

Configuring Nagios

Now that Nagios is up and running, you’ll want to configure it to monitor your specific infrastructure. Here are some key configuration files to be aware of:

• /etc/nagios/nagios.cfg: Main configuration file
• /etc/nagios/objects/commands.cfg: Defines check commands
• /etc/nagios/objects/contacts.cfg: Configures notification contacts
• /etc/nagios/objects/timeperiods.cfg: Sets monitoring time periods
• /etc/nagios/objects/templates.cfg: Contains templates for hosts and services

To add new hosts or services to monitor, create new configuration files in the /etc/nagios/conf.d/ directory. For example:

sudo nano /etc/nagios/conf.d/myserver.cfg

Add your host and service definitions to this file. Here’s a basic example:

define host {
    use                     linux-server
    host_name               myserver
    alias                   My Linux Server
    address                 192.168.1.100
    max_check_attempts      5
    check_period            24x7
    notification_interval   30
    notification_period     24x7
}

define service {
    use                     generic-service
    host_name               myserver
    service_description     PING
    check_command           check_ping!100.0,20%!500.0,60%
}

After making changes to any configuration files, always verify the configuration and restart Nagios:

sudo /usr/sbin/nagios -v /etc/nagios/nagios.cfg
sudo systemctl restart nagios

Troubleshooting Tips

If you encounter issues with Nagios, try these troubleshooting steps:

1. Check Nagios logs for error messages:

sudo tail -f /var/log/nagios/nagios.log

2. Verify SELinux is not blocking Nagios:

sudo setenforce 0

If Nagios starts working, you may need to configure SELinux policies for Nagios.

3. Ensure all required ports are open in your firewall:

sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --reload

4. Verify file permissions:

sudo chown -R nagios:nagios /etc/nagios
sudo chmod -R 775 /etc/nagios

Congratulations! You have successfully installed Nagios. Thanks for using this tutorial for installing the Nagios open-source monitoring on AlmaLinux 9. system. For additional help or useful information, we recommend you check the Nagios website.