March 28, 2025

Efficient Server Monitoring with NCPA and Nagios XI on RHEL 9

Tucker Falen

Effective server monitoring is crucial for maintaining optimal system performance and addressing issues before they escalate. The Nagios Cross-Platform Agent (NCPA) is a lightweight, agent-based tool that simplifies real-time monitoring for Linux systems like Red Hat Enterprise Linux (RHEL) 9. Unlike SNMP, NCPA uses a secure, RESTful API to collect detailed system metrics, offering a powerful and secure solution for integration with Nagios XI. This guide will walk you through the installation and configuration process of NCPA on RHEL 9, enabling comprehensive system monitoring through Nagios XI.

Prerequisites

Before proceeding, make sure you have:

A RHEL 9 system with root or sudo privileges.
Nagios XI is installed and accessible, with the NCPA Wizard enabled.
A stable internet connection for package downloads.
SELinux set to enforcing or permissive (check with getenforce; adjust if needed).

Step 1: Install the Nagios Repository

The recommended method for installing NCPA on RHEL 9 is by using the Nagios repository. To add the repository, run:

sudo rpm -Uvh https://repo.nagios.com/nagios/9/nagios-repo-9-2.el9.noarch.rpm
sudo dnf update

After adding the repository, update your package list:

sudo dnf clean all
sudo dnf update -y

Step 2: Install NCPA on RHEL 9

Once the repository is set up, install the NCPA agent using:

sudo dnf install ncpa -y

Verify the installation:

rpm -q ncpa

Expected output:

ncpa-.el9.x86_64 (e.g., ncpa-3.1.1-1.el9.x86_64)

Step 3: Configure NCPA

After installation, configure NCPA by editing the configuration file to set your API token:

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

Find the line:

community_string = mytoken

Replace mytoken with a strong, unique token (e.g., K9pL3mX7vR2tQ8nJ), ensuring it is not predictable for security reasons.

Save the file (CTRL + X, then Y, and Enter).

Step 4: Enable and Start the NCPA Service

To ensure NCPA runs automatically at boot and starts immediately, run:

sudo systemctl enable ncpa
sudo systemctl start ncpa

Check if the service is running:

sudo systemctl status ncpa

Confirm that the output shows Active: active (running).

Step 5: Configure Firewall Rules

If firewalld is active (check with sudo systemctl status firewalld), allow NCPA traffic on port 5693:

sudo firewall-cmd --zone=public --add-port=5693/tcp --permanent
sudo firewall-cmd --reload

Confirm firewall rules:

sudo firewall-cmd --list-ports

Step 6: Test NCPA Installation

After configuring the firewall, confirm that NCPA is accessible by navigating to:

https://NCPA_IP_ADDRESS:5693/

Since NCPA uses a self-signed certificate, your browser may display a warning. Click Advanced > Proceed to continue.

You should see the NCPA login page. Enter the API token you configured earlier and click Log In.

Step 7: Add RHEL 9 Host to Nagios XI Using NCPA Wizard

Navigate to Configure > Configuring Wizard.

Search for and select NCPA.

Enter the RHEL 9 server’s IP address and the API token.

Click Next, then select the system metrics to monitor (CPU, memory, disk, network traffic, etc.).

Apply the configuration and verify that Nagios XI is collecting data from your RHEL 9 host.

Common Issues & Fixes

NCPA Service is Not Running

Check logs for errors:

sudo journalctl -u ncpa --no-pager | tail -20

Restart NCPA if necessary:

sudo systemctl restart ncpa

Host Appears “Down” in Nagios XI

Check firewall rules:

sudo firewall-cmd --list-ports

Ensure NCPA is running:

sudo systemctl status ncpa

Verify the Nagios XI configuration.

Incorrect API Token Error

Confirm the correct API token is set in ncpa.cfg.
Restart the NCPA service after changes: bashCopysudo systemctl restart ncpa

Conclusion

You have successfully installed and configured NCPA on RHEL 9 for monitoring with Nagios XI. This setup enables you to efficiently track system performance metrics and ensure proactive issue resolution.