This guide will take you through the complete process of setting up SNMP on AlmaLinux 8, integrating it with Nagios XI, and enabling real-time monitoring for proactive issue resolution and improved system reliability.

Prerequisites

Before proceeding, ensure the following:

• An AlmaLinux 8 system 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 AlmaLinux 8

1. To install SNMP and the required libraries, run:

sudo dnf install net-snmp net-snmp-utils -y

sudo dnf install net-snmp net-snmp-utils -y

2. After installation, verify the installed version:

snmpd -v

snmpd -v

Step 2: Configure SNMP Access

SNMP v2c Configuration

1. Create a backup of the existing configuration:

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

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

2. Edit the SNMP configuration file:

sudo nano /etc/snmp/snmpd.conf

sudo nano /etc/snmp/snmpd.conf

3. Replace or update the line with your community string and Nagios XI IP:

rocommunity Str0ngC0mmunity 10.25.5.12

rocommunity Str0ngC0mmunity 10.25.5.12

4. Save the file and restart SNMP:

sudo systemctl restart snmpd.service

sudo systemctl restart snmpd.service

SNMP v3 Configuration (More Secure)

1. Stop the SNMP service temporarily:

sudo systemctl stop snmpd.service

sudo systemctl stop snmpd.service

2. 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

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

3. Restart the SNMP service:

sudo systemctl restart snmpd.service

sudo systemctl restart snmpd.service

Step 3: Configure Firewall Rules

1. If firewalld is active, allow SNMP traffic on UDP port 161:

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

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

2. Confirm firewall rules:

sudo firewall-cmd --list-ports

sudo firewall-cmd --list-ports

Step 4: Enable SNMP Service on Boot

To ensure SNMP starts automatically at boot:

sudo systemctl enable snmpd.service

sudo systemctl enable snmpd.service

Step 5: Test SNMP Communication

From your Nagios XI server:

For SNMP v2c:

snmpwalk -v2c -c Str0ngC0mmunity 10.25.5.12

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

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 almalinux8 ..."

iso.3.6.1.2.1.1.1.0 = STRING: "Linux almalinux8 ..."

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

Step 6: Add AlmaLinux 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 AlmaLinux 8 server’s IP address and SNMP credentials

5. Click Next, select the system metrics to monitor (CPU, memory, disk, 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

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

Restart SNMP if necessary:

sudo systemctl restart snmpd.service

sudo systemctl restart snmpd.service

Host Appears “Down” in Nagios XI

Check firewall rules:

sudo firewall-cmd --list-ports

sudo firewall-cmd --list-ports

Ensure SNMP is running:

sudo systemctl status snmpd

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

You’ve successfully configured SNMP on AlmaLinux 8 for agentless monitoring with Nagios XI, providing real-time system insights. For advanced setups, explore custom SNMP OIDs or additional Nagios XI plugins.

For support:

• Nagios Support Forum
• Nagios Knowledgebase

This guide walks you through the installation and configuration process of NCPA on AlmaLinux 8, enabling comprehensive system monitoring through Nagios XI.

Prerequisites

Before proceeding, ensure you have:

• An AlmaLinux 8 system with root or sudo privileges
• Nagios XI 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 AlmaLinux 8 is using the Nagios repository:

sudo rpm -Uvh https://repo.nagios.com/nagios/8/nagios-repo-8-1.el8.noarch.rpm
sudo yum update -y

sudo rpm -Uvh https://repo.nagios.com/nagios/8/nagios-repo-8-1.el8.noarch.rpm
sudo yum update -y

After adding the repository, refresh your package list:

sudo dnf clean all
sudo dnf update -y

sudo dnf clean all
sudo dnf update -y

Step 2: Install NCPA on AlmaLinux 8

Install the NCPA agent using:

sudo dnf install ncpa -y

sudo dnf install ncpa -y

Verify installation:

rpm -q ncpa

rpm -q ncpa

Expected output: ncpa-<version>.el8.x86_64

Step 3: Configure NCPA

Edit the NCPA configuration file to set your API token:

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

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

Find the line:

community_string = mytoken

community_string = mytoken

Replace mytoken with a strong, unique token (e.g., K9pL3mX7vR2tQ8nJ). Save and close.

Step 4: Enable and Start the NCPA Service

Ensure NCPA runs at boot and starts now:

sudo systemctl enable ncpa
sudo systemctl start ncpa
sudo systemctl status ncpa

sudo systemctl enable ncpa
sudo systemctl start ncpa
sudo systemctl status ncpa

Confirm active (running) is displayed.

Step 5: Configure Firewall Rules

If firewalld is active, open port 5693:

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

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

Verify:

sudo firewall-cmd --list-ports

sudo firewall-cmd --list-ports

Step 6: Test NCPA Installation

Verify access to NCPA by visiting:

https://<AlmaLinux8-IP>:5693/

https://<AlmaLinux8-IP>:5693/

Accept the browser’s self-signed certificate warning. Enter your API token and log in.

Step 7: Add AlmaLinux 8 Host to Nagios XI Using NCPA Wizard

1. Log into Nagios XI.

2. Navigate to Configure > Configuration Wizards.

3. Search for and select NCPA.

4. Enter the AlmaLinux 8 server’s IP and the API token.

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

6. Apply configuration and verify data collection.

Common Issues & Fixes

NCPA Service is Not Running

Check logs:

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

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

Restart NCPA if needed:

sudo systemctl restart ncpa

sudo systemctl restart ncpa

Host Appears “Down” in Nagios XI

Check firewall rules:

sudo firewall-cmd --list-ports

sudo firewall-cmd --list-ports

Check NCPA status:

sudo systemctl status ncpa

sudo systemctl status ncpa

Verify Nagios XI configuration.

Incorrect API Token Error

Ensure correct token is set in ncpa.cfg. Restart NCPA after updates:

sudo systemctl restart ncpa

sudo systemctl restart ncpa

Conclusion

You have successfully installed and configured NCPA on AlmaLinux 8 for monitoring with Nagios XI. This setup enables efficient tracking of system performance metrics and supports proactive issue resolution.

For additional support:

• Nagios Support Forum
• Nagios Knowledgebase