Knowledgebase

MQTT is a publish/subscribe model based, "lightweight" messaging protocol over TCP/IP for communication between "Internet of Things" devices such as ESP8266, Raspberry Pi, etc. It is very popular with low resources and battery powered applications such as home automation, security alarm systems and battery-powered sensor networks.

Mosquitto is an open source message broker (or server) that implements MQTT protocols. With its good community support, documentation, and ease of installation it has become one of the most popular MQTT brokers.

##Prerequisites

• An Ubuntu 16.04 server with root access
• Open port TCP:1883 on firewall

##Step One: Install Mosquitto Broker

Update Ubuntu's package list and install the latest Mosquitto Broker available from it

sudo apt-get update
sudo apt-get install mosquitto

The Mosquitto service will start after installation.

##Step Two: Install the Clients and Test

Install MQTT clients

sudo apt-get install mosquitto-clients

Mosquitto clients help us easily test MQTT through a command line utility. We will use two command windows, one to subscribe to a topic named "test" and one to publish a message to it.

Topics are labels used by the broker to filter messages for each connected client. A client program subscribed to a topic "Home1/BedroomTemp" will only listen to messages published to the same topic by other clients.

Subscribe to topic "test"

mosquitto_sub -t "test"

Mosquito_sub is a subscribe client we installed in the previous command. Here we are specifying "-t" followed by a topic name.

Publish a message to topic "test"

Login to the terminal as a second instance and publish a message to the "test" topic.

mosquitto_pub -m "message from mosquitto_pub client" -t "test"

Here the additional parameter "–m" is followed by the message we want to publish. Hit "Enter" and you should see a message from mosquitto_pub client displayed in other terminal where mosquito_sub client is running.

##Step Three: Secure with a Password

Mosquitto comes with a password file generating utility called mosquitto_passwd.

sudo mosquitto_passwd -c /etc/mosquitto/passwd dave
Password: password

Create a configuration file for Mosquitto pointing to the password file we have just created.

sudo nano /etc/mosquitto/conf.d/default.conf

This will open an empty file. Paste the following into it.

allow_anonymous false
password_file /etc/mosquitto/passwd

Save and exit the text editor with "Ctrl+O", "Enter" and "Ctrl+X".

Now restart Mosquitto server and test our changes.

sudo systemctl restart mosquitto

In the subscribe client window, press "Ctrl+C" to exit the subscribe client and restart it with following command.

mosquitto_sub -t "test" -u "dave" -P "password"

Note the capital -P here.

In the publish client window, try to publish a message without a password.

mosquitto_pub -t "test" -m "message from mosquitto_pub client"

The message will be rejected with following error message.

Connection Refused: not authorised.
Error: The connection was refused.

Now publish a message with the username and password.

mosquitto_pub -t "test" -m "message from mosquitto_pub client" -u "dave" -P "password"

Hit "Enter" and you will see the message in subscribe client window, as in Step Two.

##Conclusion

We have now set up a password protected MQTT server. You can use the Public IP of your Ubuntu server as an MQTT broker for your projects.