Monitoring Oracle Linux 8 with SNMP in Nagios XI: A Step-by-Step Guide

Maintaining the stability and performance of Linux servers is crucial for a robust IT infrastructure. SNMP (Simple Network Management Protocol) provides a streamlined, agentless approach to monitoring Oracle Linux 8 with Nagios XI, offering real-time visibility into system metrics without the complexity of additional software agents.

This guide will take you through each step of configuring SNMP on Oracle Linux 8, ensuring seamless integration with Nagios XI for efficient monitoring and early issue detection.

Prerequisites

Before proceeding, ensure the following:

• A system running Oracle Linux 8 with root or sudo privileges.
• Nagios XI installed and accessible, with the SNMP Wizard enabled.
• A stable internet connection for package downloads.

Step 1: Install SNMP on Oracle Linux 8

To install SNMP and the required libraries, update the system first:

sudo yum update -y

Then, install net-snmp:

sudo yum install net-snmp -y

Verify the installation:

snmpd -v

This confirms that SNMP is correctly installed on the system.

Step 2: Configure SNMP Access

SNMP v2c Configuration

To configure SNMP v2c, create a backup of the existing configuration:

sudo cp /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.bak

Now, edit the SNMP configuration file:

sudo nano /etc/snmp/snmpd.conf

Find and modify the following line to define the community string and allow access from your Nagios XI server (replace Str0ngC0mmunity with your desired community string and 10.25.5.12 with your Nagios XI server’s IP address):

rocommunity Str0ngC0mmunity 10.25.5.12

Save the file and restart the SNMP service:

sudo systemctl restart snmpd.service

SNMP v3 Configuration (More Secure)

To configure SNMP v3, create an SNMP user with authentication and encryption:

sudo net-snmp-create-v3-user -ro -a SHA -A Str0ng@uth3ntic@ti0n -x AES -X Str0ngPriv@cy nagios

• -a SHA → Specifies SHA for authentication (MD5 is also supported but less secure).
• -x AES → Enables AES encryption (DES is another option but less secure).

Restart the SNMP service:

sudo systemctl restart snmpd.service

Step 3: Configure Firewall Rules

If firewalld is enabled on your system, allow SNMP traffic on UDP port 161:

sudo firewall-cmd --zone=public --add-port=161/udp --permanent
sudo firewall-cmd --reload

Confirm firewall rules:

sudo firewall-cmd --list-ports

Step 4: Enable SNMP Service on Boot

To ensure SNMP starts automatically at boot, run:

sudo systemctl enable snmpd.service

Step 5: Test SNMP Communication

To test if SNMP is responding correctly, run the following commands from your Nagios XI server.

For SNMP v2c:

snmpwalk -v2c -c Str0ngC0mmunity 10.25.5.12

For SNMP v3:

snmpwalk -v3 -u nagios -l authPriv -a SHA -A Str0ng@uth3ntic@ti0n -x AES -X Str0ngPriv@cy 10.25.5.12

Expected Output (Example)

iso.3.6.1.2.1.1.1.0 = STRING: "Linux myserver 5.15.0-100.el8.x86_64"
iso.3.6.1.2.1.1.3.0 = Timeticks: (100032) 0:16:40.32

If the command does not return data, review SNMP configuration and firewall settings.

Step 6: Add Oracle Linux 8 Host to Nagios XI Using SNMP Wizard

1. Log in to Nagios XI.

2. Navigate to Configure > Run a configuring wizard.

3. Search for and select Linux SNMP wizard.

4. Enter the Oracle Linux 8 server’s IP address and SNMP credentials.

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

6. Apply the configuration and verify that Nagios XI is collecting SNMP data.

Common Issues & Fixes

SNMP Service is Not Running

Check logs for errors:

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

Restart SNMP if necessary:

sudo systemctl restart snmpd.service

Host Appears “Down” in Nagios XI

• Check firewall rules: sudo firewall-cmd --list-ports
• Ensure SNMP is running: sudo systemctl status snmpd
• Verify Nagios XI configuration

Incorrect SNMP Credentials Error

• Confirm the correct community string (SNMP v2c) or authentication details (SNMP v3).
• Restart the SNMP service after changes.

Conclusion

By following this guide, you have successfully installed and configured SNMP on Oracle Linux 8 for monitoring with Nagios XI. This setup provides a robust, agentless solution for tracking system performance metrics and ensuring proactive issue resolution.

For further assistance, refer to the Nagios Support Forum or the Nagios Knowledgebase.