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.

Mosquitto MQTT Client Raspberry Pi

Updated 15 December 2021

Recommended resources:

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:

[email protected]:~ $ sudo apt install -y mosquitto mosquitto-clients

Run Mosquitto on the background as a daemon:

[email protected]:~ $ mosquitto -d

Subscribing to testTopic Topic

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

[email protected]:~ $ mosquitto_sub -d -t testTopic
Mosquitto MQTT Client subscribe to topic

You’re now subscribed to a topic called testTopic.

Publishing “Hello World!” Message to testTopic Topic

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

[email protected]:~$ mosquitto_pub -d -t testTopic -m "Hello world!"

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

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:

[email protected]:~ $ mosquitto_sub -d -t testTopic

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

[email protected]:~$ mosquitto_pub -d -t testTopic -m "Hello world!"

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. Now, you can experiment with MQTT in your ESP32/ESP8266 IoT projects. We have several MQTT practical examples that you can experiment with. Here are some examples:

You can also run Mosquitto MQTT broker on the cloud. Running an MQTT Mosquitto Broker in the cloud allows you to connect several ESP32/ESP8266 boards and other IoT devices from anywhere using different networks as long as they have an Internet connection. Check the tutorial below:

Like home automation? Learn more about Node-RED, Raspberry Pi, ESP8266, and Arduino with our course: Build a Home Automation System for $100.

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

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Build Web Server projects with the ESP32 and ESP8266 boards to control outputs and monitor sensors remotely. Learn HTML, CSS, JavaScript and client-server communication protocols DOWNLOAD »

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17 thoughts on “Testing Mosquitto Broker and Client on Raspberry Pi”

  1. Hi Rui, Odd things happening for me on this one. I am using a Rpi2b, Raspian Pixel, Mosquitto ver 1.4.14. When I type in the second terminal window “mosquitto_pub -d -t testTopic -m “Hello World” the following occurs:
    1 I receive an Error: Unknown option ‘world’
    2 I noticed when I typed the command again on the first depression of the quote (shift + ‘) the quote did not show. (it does show in text editor).
    AND if I type “mosquitto_pub -d -t testTopic -m Hello World (without the quotes) I get the same error, but if I type mosquitto_pub -d -t testTopic -m Hello, the message “Hello” is transmitted. Any thoughts on this?

  2. awesome tutorial, thanks. So many questions answered in my head, going through it and seeing it work really helps the understanding.

  3. Hi Rui,
    This is a very helpful tutorial series for someone starting with MQTT. May I suggest that the flow of the process would be easier to follow if the order of the Terminal window images was changed. The window where the command is entered should appear first, followed by the windows where the message is received.
    Also, in the paragraph before Wrapping Up, you mention “a device could publish messages to multiple devices”. This contradicts your earlier explanation that messages are published to TOPICS, and devices must subscribe to topics to receive messages.
    I’ve been following RNT for a few years and learned a lot. Keep up the great work.

    • Hello Michael. Thanks for the helpful feedback!
      Both statements are true. Multiple boards can be subscribed to the same topic. So, one board can publish readings to all devices subscribed to that topic.
      I’m glad you’ve found our content helpful.

  4. Thank yo so much for this instruction I have a raspberry pi 3 so installed raspberry OS as standard then followed your instructions, I then installed Mosquito then opened two terminal windows and followed your instructions for Hello world and job done
    it appeared in the other window I was amazed that it all just worked as I want to learn MQTT for my Wemose D1 min and ESP32 and ESP8266 and ESP32-cam that I have and would like to make up some sort of small system
    I can then get away from Ewe link and China but I did not want to use HA as it is to big for me and two complicated and all the cloud services are slow the latency takes too long with Ewe Link and this was instant I have tried Telegram tutorial that you provided and that worked for two days then just stopped so gave up with that.
    I would like to take this opportunity to thank you for a wonderful YouTube channel and all your hard work you are the best at describing a project and your written word is second to none you go the extra mile to explain it all and make it very easy to follow.
    I would like to purchase your book but I am not sure of the best one?
    Many thanks Bob in the UK

  5. Bonjour,
    Je découvre MQTT pour la première fois. Les explications et les tests me permettent de vraiment mieux comprendre les commandes exécutées pas à pas.

    Merci encore de votre implication

  6. Hi. I guess default port number is 1883 for MQTT and 8883 for MQTTS.
    Do you know how to change port for daemon.
    It starts on 1883 port number even though updating listener to 8883 in mosquitto.conf.

  7. Client (null) sending CONNECT
    Client (null) received CONNACK (5)
    Connection error: Connection Refused: not authorised.
    Client (null) sending DISCONNECT

    Hi I’m getting this error when I’m trying to subscribe to the testTopic.

    Could you guide me through this.


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