How to Monitor CentOS 8 with SNMP in Nagios XI

SNMP (Simple Network Management Protocol) isa powerful tool for monitoring network devices and servers. This guide will walk you through installing and configuring SNMP on CentOS 8.

Step 1: Install SNMP and Utilities

CentOS 8 uses dnf as the default package manager. Install SNMP packages with:

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

Step 2: Start and Enable the SNMP Service

Once installed, start and enable the SNMP service so that it runs at boot:

sudo systemctl enable --now snmpd

Step 3: Configure SNMP

The main configuration file for SNMP is located at:

/etc/snmp/snmpd.conf

Before making changes, back up the original file:

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

Now, edit the configuration file:

sudo nano /etc/snmp/snmpd.conf

Modify or add the following lines to set up SNMPv2c with a community string (replace YourCommunity with a strong name):

com2sec readonly  default  YourCommunity
group   MyROGroup v2c        readonly
view    all    included   .1
access  MyROGroup ""      any       noauth    exact  all    none   none
syslocation "Data Center"
syscontact "Admin <admin@example.com>"

Save and exit the file, then restart the SNMP service:

sudo systemctl restart snmpd

Step 4: Adjust Firewall Rules

To allow SNMP traffic, open the necessary UDP port (161):

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

Step 5: Verify SNMP Functionality

Test if SNMP is working correctly with:

snmpwalk -v2c -c YourCommunity -O e 127.0.0.1

If you see output with system information, SNMP is working correctly.

Step 6: Open Firewall for SNMP

If you want to allow SNMP traffic from remote machines, open the firewall to allow SNMP traffic:

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

This command opens port 161 (the default SNMP port) for UDP traffic, allowing SNMP queries from remote systems.

Step 7: Test SNMP from a Remote System

Finally, to ensure SNMP is accessible remotely, test it from another system using snmpwalk:

snmpwalk -v2c -c YourCommunityString

Replace <server-ip> with the IP address of your CentOS server. If SNMP is correctly configured, you will receive SNMP data from the remote server.

Monitoring with Nagios XI

On Nagios XI navigate to Run a Wizard and click on the SNMP wizard

Add your Host Name and type in the SNMP Community string that you created.

Pick the SNMP Services that you want to monitor and then click Next and Finish with Defaults.

Conclusion

You have successfully installed and configured SNMP on CentOS 8. This setup allows your server to be monitored remotely, enhancing network management capabilities. You also configured SNMP monitoring with Nagios XI, which provides a powerful interface for tracking system performance and network activity. By adding your SNMP-enabled server to Nagios XI, you can gain deeper insights into system health, set up alerts, and optimize network monitoring for better performance.