Testing Mosquitto Broker and Client on Raspberry Pi

In this tutorial, you’re going to test the Mosquitto MQTT Broker and MQTT Client on a Raspberry Pi. You’ll subscribe the MQTT client to an MQTT topic and publish sample messages.

Recommended resources:

• You need a Raspberry Pi board – read Best Raspberry Pi Starter Kits
• Install Raspberry Pi OS, Set Up Wi-Fi, Enable and Connect with SSH
• How to Install Mosquitto Broker on Raspberry Pi
• What is MQTT and How It Works
• Getting Started with Node-RED on Raspberry Pi

Testing MQTT Broker Installation

After installing MQTT Broker, I recommend installing an MQTT Client to test the Broker installation and publish sample messages.

Run the following command to install MQTT Mosquitto Client:

sudo apt install -y mosquitto mosquitto-clients

Run Mosquitto in the background as a daemon:

mosquitto -d

Subscribing to testTopic Topic

To subscribe to an MQTT topic with Mosquitto Client, open a terminal Window #1 and enter the command:

mosquitto_sub -d -t testTopic

You’re now subscribed to a topic called testTopic.

If you have enabled username and password on your broker, you need to run the command as follows:

mosquitto_sub -d -t testTopic -u user -P pass

Replace user with your username and pass with your password. For example, my username is ahmed, and the password is pass1245, so I need to run the command as follows:

mosquitto_sub -d -t testTopic -u ahmed -P pass1245

Publishing “Hello World!” Message to testTopic Topic

To publish a sample message to testTopic, open a terminal Window #2 and run the following command:

mosquitto_pub -d -t testTopic -m "Hello world!"

The message “Hello World!” is received in Window #1 as illustrated in the figure above.

If you have enabled username and password on your broker, you need to run the command as follows:

mosquitto_pub -d -t testTopic -m "Hello world!" -u user -P pass

Replace user with your username and pass with your password.

Publishing a Message to Multiple Clients

Having Window #1 still subscribed to topic testTopic, open a new terminal Window #3 and run this command to subscribe to testTopic topic:

mosquitto_sub -d -t testTopic

If you have enabled username and password on your broker, you need to run the command as follows:

mosquitto_sub -d -t testTopic -u user -P pass

Replace user with your username and pass with your password.

On Window #2 publish the “Hello World!” message:

mosquitto_pub -d -t testTopic -m "Hello world!"

If you have enabled username and password on your broker, you need to run the command as follows:

mosquitto_pub -d -t testTopic -m "Hello world!" -u user -P pass

Since two clients are subscribed to testTopic topic, they will both receive the “Hello world!” message.

This simple example shows how MQTT works and how your devices (for example: ESP8266 or ESP32, etc.) can be subscribed to the same topic to receive messages, or a device can publish messages to multiple devices.

Wrapping Up

In this tutorial, you checked that your Mosquitto Broker installed on the Raspberry Pi is running properly.

Do you have any questions? Leave a comment down below!