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SNMP Custom Service Template

v1.0.0

Table of contents

Overview

SNMP Custom Service Template is a template repository based on a ready-to-use SNMP (Simple Network Management Protocol) server for Linux systems (Ubuntu 22.04 and 24.04). It extends the standard SNMP daemon with a Python script, allowing you to define and serve your own SNMP OIDs and commands without modifying the SNMP server source code.

This template is designed for system integrators and developers who need to expose custom system metrics or control endpoints via SNMP, beyond what is available in standard SNMP agents. The included Python script works together with the SNMP daemon using the pass-persist mechanism, enabling you to implement any custom SNMP command or data point in Python.

Main value:

  • Quickly add custom SNMP endpoints to your Linux system for integration with network monitoring tools
  • No need to write C/C++ SNMP agents—just extend the provided Python script
  • Leverages the standard SNMP server for authentication, security, and protocol handling, while your logic runs in Python

This approach is ideal if you want to monitor or control custom aspects of your system via SNMP, using a familiar scripting language and standard Linux SNMP infrastructure.

Versions

Table 1 - Application versions.

Version Release date What’s new
1.0.0 20.08.2025 - Initial release of SNMP Custom Service Template.

Files

The SNMP Custom Service Template includes the following components:

README.md --------------------------- Documentation and installation guide.
snmp_main.py ------------------------ Main SNMP agent Python script.
snmp_payload.py --------------------- SNMP payload handler and system monitoring.
snmpd.conf -------------------------- SNMP daemon configuration file.
CUSTOM-AGENT-MIB.txt ---------------- Main MIB definition file for the custom agent.
OID_list.txt ------------------------ OID reference and usage examples.
install.sh -------------------------- Installation script for SNMP packages.
test_snmp.sh ------------------------ Test script for SNMP agent.
libs/ ------------------------------- Folder with SNMP packages for different Ubuntu versions.
    22.04/ -------------------------- SNMP packages for Ubuntu 22.04.
        libsnmp-base_5.9.3+dfsg-1ubuntu1.4_all.deb
        libsnmp40_5.9.3+dfsg-1ubuntu1.4_amd64.deb
        snmp_5.9.3+dfsg-1ubuntu1.4_amd64.deb
        snmpd_5.9.3+dfsg-1ubuntu1.4_amd64.deb
    24.04/ -------------------------- SNMP packages for Ubuntu 24.04.
        libsnmp-base_5.9.4+dfsg-1.1ubuntu3.1_all.deb
        libsnmp40t64_5.9.4+dfsg-1.1ubuntu3.1_amd64.deb
        snmp_5.9.4+dfsg-1.1ubuntu3.1_amd64.deb
        snmpd_5.9.4+dfsg-1.1ubuntu3.1_amd64.deb

Key Features

Key features include:

  • System Monitoring: CPU load, memory usage, temperature monitoring
  • Service Status: Service health and uptime reporting
  • Secure Access: SNMPv3 with authentication and encryption
  • Standard Compliance: Compatible with any SNMP monitoring tool
  • Comprehensive Logging: Detailed logging with rotation capabilities
  • MIB Support: Complete MIB definitions for standard SNMP tool integration
  • Easy Customization: Modular design for extending monitoring capabilities

Installation Instructions

Install SNMP packages

Install the .deb packages from the libs folder specific to your Ubuntu version:

For Ubuntu 24.04:

cd libs/24.04
sudo dpkg -i libsnmp-base_5.9.4+dfsg-1.1ubuntu3.1_all.deb
sudo dpkg -i libsnmp40t64_5.9.4+dfsg-1.1ubuntu3.1_amd64.deb
sudo dpkg -i snmp_5.9.4+dfsg-1.1ubuntu3.1_amd64.deb
sudo dpkg -i snmpd_5.9.4+dfsg-1.1ubuntu3.1_amd64.deb

For Ubuntu 22.04:

cd libs/22.04
sudo dpkg -i libsnmp-base_5.9.3+dfsg-1ubuntu1.4_all.deb
sudo dpkg -i libsnmp40_5.9.3+dfsg-1ubuntu1.4_amd64.deb
sudo dpkg -i snmp_5.9.3+dfsg-1ubuntu1.4_amd64.deb
sudo dpkg -i snmpd_5.9.3+dfsg-1ubuntu1.4_amd64.deb

If you encounter dependency issues:

sudo apt-get install -f

Verify the installation:

dpkg -l | grep snmp

Stop the SNMP service 

sudo systemctl stop snmpd.service

Deploy the custom SNMP agent

Create the application directory:

sudo mkdir -p /opt/snmp-agent

Copy the Python scripts:

sudo cp snmp_main.py /opt/snmp-agent/
sudo cp snmp_payload.py /opt/snmp-agent/

Make scripts executable:

sudo chmod +x /opt/snmp-agent/snmp_main.py
sudo chmod +x /opt/snmp-agent/snmp_payload.py

Configure the SNMP daemon

Replace /etc/snmp/snmpd.conf with the provided configuration:

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

Configure the service to run as root

Edit the systemd service file:

sudo nano /lib/systemd/system/snmpd.service

Remove -u Debian-snmp -g Debian-snmp from the ExecStart line.

Create the log directory 

sudo mkdir -p /var/log/snmp-agent
sudo chmod 755 /var/log/snmp-agent

Start the service 

sudo systemctl daemon-reload
sudo systemctl enable snmpd.service
sudo systemctl start snmpd.service

Testing the Installation

Test the SNMP service:

# Test service status
snmpget -v3 -u snmpuser -l authPriv -a SHA -A "SecurePass123" -x AES -X "SecurePass123" localhost .1.3.6.1.4.1.12345.2.4

# Test system uptime
snmpget -v3 -u snmpuser -l authPriv -a SHA -A "SecurePass123" -x AES -X "SecurePass123" localhost .1.3.6.1.4.1.12345.2.5

# Test CPU load
snmpget -v3 -u snmpuser -l authPriv -a SHA -A "SecurePass123" -x AES -X "SecurePass123" localhost .1.3.6.1.4.1.12345.2.3.1

Automated Testing Script

You can also use the provided test_snmp.sh script to automatically test your SNMP agent setup and all custom OIDs.

Make the script executable (if needed):

chmod +x test_snmp.sh

Run the script:

./test_snmp.sh

The script will:

  • Check if snmpget is installed and if the snmpd service is running
  • Test basic SNMP connectivity
  • Test all custom OIDs (service status, uptime, CPU load, memory, temperature)
  • Perform an SNMP walk on your custom OID tree
  • Print a summary of the results

If all tests pass, your SNMP agent is working correctly!

Configuration

SNMP Credentials

  • Username: snmpuser
  • Auth Protocol: SHA
  • Auth Password: SecurePass123
  • Privacy Protocol: AES
  • Privacy Password: SecurePass123

Custom OID Tree

Base OID: .1.3.6.1.4.1.12345.2

Available endpoints:

  • .1.3.6.1.4.1.12345.2.4 - Service Status
  • .1.3.6.1.4.1.12345.2.5 - System Uptime
  • .1.3.6.1.4.1.12345.2.3.1 - CPU Load Averages
  • .1.3.6.1.4.1.12345.2.3.2 - Memory Usage
  • .1.3.6.1.4.1.12345.2.3.3 - CPU Temperature

MIB Documentation

The template includes comprehensive Management Information Base (MIB) files for integration with standard SNMP monitoring tools.

MIB Files

The service includes custom MIB definitions for SNMP monitoring:

  • CUSTOM-AGENT-MIB.txt: Main MIB definition file for the custom SNMP agent
  • Enterprise OID: .1.3.6.1.4.1.12345
  • Custom Agent Base: .1.3.6.1.4.1.12345.2

OID Structure 

.1.3.6.1.4.1.12345.2          (customAgent)
├── .4                         (serviceStatus)
├── .5                         (systemUptime)
└── .3                         (systemInfo)
    ├── .1                     (cpuLoadAverages)
    ├── .2                     (memoryUsage)
    └── .3                     (cpuTemperature)

Installing MIB Files

To use MIB files with SNMP tools:

Copy MIB files to system directory:

sudo cp CUSTOM-AGENT-MIB.txt /usr/share/snmp/mibs/

Or specify MIB directory when using SNMP tools:

snmpget -M +. -m CUSTOM-AGENT-MIB -v3 -u snmpuser -l authPriv \
        -a SHA -A "SecurePass123" -x AES -X "SecurePass123" \
        localhost serviceStatus.0

Using Symbolic Names

With properly installed MIBs, you can use symbolic names instead of numeric OIDs:

# Instead of: .1.3.6.1.4.1.12345.2.4
snmpget -v3 -u snmpuser -l authPriv -a SHA -A "SecurePass123" \
        -x AES -X "SecurePass123" localhost serviceStatus.0

# Instead of: .1.3.6.1.4.1.12345.2.3.1  
snmpget -v3 -u snmpuser -l authPriv -a SHA -A "SecurePass123" \
        -x AES -X "SecurePass123" localhost cpuLoadAverages.0

MIB Validation

Validate MIB syntax using:

smilint CUSTOM-AGENT-MIB.txt

Install smilint if needed:

sudo apt-get install libsmi2-dev libsmi2-common

Enterprise Number Registration

To customize for your organization:

  1. Get your enterprise number from IANA
  2. Replace 12345 with your registered enterprise number in the MIB file
  3. Update organization info (ORGANIZATION and CONTACT-INFO fields) in the MIB file
  4. Add new objects by defining additional OBJECT-TYPE entries as needed
  5. Update descriptions (DESCRIPTION fields) for your specific use case

Customization

Changing the Enterprise OID

  1. Edit snmp_payload.py and change BASE_OID
  2. Edit snmpd.conf and update the pass_persist line
  3. Update the MIB file CUSTOM-AGENT-MIB.txt with your enterprise number
  4. Update your monitoring tools configuration accordingly

Adding New Monitoring Points

  1. Add new functions in snmp_payload.py
  2. Update the get_board_option() function to handle new OID endpoints
  3. Update the MIB file CUSTOM-AGENT-MIB.txt to document the new endpoints
  4. Test new endpoints with SNMP tools

Changing Authentication

  1. Edit snmpd.conf
  2. Update the createUser line with new credentials
  3. Update the rouser line accordingly

Troubleshooting

Check the service status 

sudo systemctl status snmpd.service

View logs 

# SNMP daemon logs
sudo journalctl -u snmpd.service -f

# Custom agent logs
sudo tail -f /var/log/snmp-agent/SNMP.log

Test the connectivity 

# Test if SNMP is listening
sudo netstat -ulnp | grep :161

# Test basic SNMP response
snmpget -v2c -c public localhost .1.3.6.1.2.1.1.1.0

Security Notes

  • Change default passwords in production
  • Consider firewall rules for port 161
  • Use strong authentication credentials
  • Regularly update SNMP packages
  • Monitor access logs for unauthorized attempts

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