MQTT is a machine-to-machine messaging protocol, designed to provide lightweight publish/subscribe communication to “Internet of Things” devices. Mosquitto is a popular MQTT server (or broker, in MQTT parlance) that has great community support and is easy to install and configure.
In this condensed quickstart tutorial we’ll install and configure Mosquitto, and use Let’s Encrypt SSL certificates to secure our MQTT traffic. If you need more in-depth coverage of any of the steps, please review the following tutorials:
Before starting this tutorial, you will need:
- An Ubuntu 18.04 server with a non-root, sudo-enabled user and basic firewall set up, as detailed in this Ubuntu 18.04 server setup tutorial
- A domain name pointed at your server. This tutorial will use the placeholder
- Port 80 must be unused on your server. If you’re installing Mosquitto on a machine with a web server that occupies this port, you’ll need to use a different method to fetch certificates, such as Certbot’s webroot mode.
Step 1 — Installing the Software
First we will install a custom software repository to get the latest version of Certbot, the Let’s Encrypt client:
- sudo add-apt-repository ppa:certbot/certbot
ENTER to accept, then install the software packages for Mosquitto and Certbot:
- sudo apt install certbot mosquitto mosquitto-clients
Next we’ll fetch our SSL certificate.
Step 2 — Downloading an SSL Certificate
Open up port
80 in your firewall:
Then run Certbot to fetch the certificate. Be sure to substitute your server's domain name here:
- sudo certbot certonly --standalone --preferred-challenges http -d mqtt.example.com
You will be prompted to enter an email address and agree to the terms of service. After doing so, you should see a message telling you the process was successful and where your certificates are stored.
We'll configure Mosquitto to use these certificates next.
Step 3 — Configuring Mosquitto
First we'll create a password file that Mosquitto will use to authenticate connections. Use
mosquitto_passwd to do this, being sure to substitute your own preferred username:
- sudo mosquitto_passwd -c /etc/mosquitto/passwd your-username
You will be prompted twice for a password.
Now open up a new configuration file for Mosquitto:
- sudo nano /etc/mosquitto/conf.d/default.conf
This will open an empty file. Paste in the following:
listener 1883 localhost
Be sure to substitute the domain name you used in Step 2 for
mqtt.example.com. Save and close the file when you are finished.
This file does the following:
- Disables anonymous logins
- Uses our password file to enable password authentication
- Sets up a unsecured listener on port 1883 for localhost only
- Sets up a secure listener on port
- Sets up a secure websocket-based listener on port
Restart Mosquitto to pick up the configuration changes:
- sudo systemctl restart mosquitto
Check to make sure the service is running again:
- sudo systemctl status mosquitto
Output● mosquitto.service - LSB: mosquitto MQTT v3.1 message broker
Loaded: loaded (/etc/init.d/mosquitto; generated)
Active: active (running) since Mon 2018-07-16 15:03:42 UTC; 2min 39s ago
Process: 6683 ExecStop=/etc/init.d/mosquitto stop (code=exited, status=0/SUCCESS)
Process: 6699 ExecStart=/etc/init.d/mosquitto start (code=exited, status=0/SUCCESS)
Tasks: 1 (limit: 1152)
└─6705 /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf
The status should be
active (running). If it's not, check your configuration file and restart again. Some more information may be available in Mosquitto's log file:
- sudo tail /var/log/mosquitto/mosquitto.log
If all is well, use
ufw to allow the two new ports through the firewall:
- sudo ufw allow 8883
- sudo ufw allow 8083
Now that Mosquitto is set up, we'll configure Certbot to restart Mosquitto after renewing our certificates.
Step 4 — Configuring Certbot Renewals
Certbot will automatically renew our SSL certificates before they expire, but it needs to be told to restart the Mosquitto service after doing so.
Open the Certbot renewal configuration file for your domain name:
- sudo nano /etc/letsencrypt/renewal/mqtt.example.com.conf
Add the following
renew_hook option on the last line:
renew_hook = systemctl restart mosquitto
Save and close the file, then run a Certbot dry run to make sure the syntax is ok:
- sudo certbot renew --dry-run
If you see no errors, you're all set. Let's test our MQTT server next.
Step 5 – Testing Mosquitto
We installed some command line MQTT clients in Step 1. We can subscribe to the topic test on the localhost listener like so:
- mosquitto_sub -h localhost -t test -u "your-user" -P "your-password"
And we can publish with
- mosquitto_pub -h localhost -t test -m "hello world" -u "your-user" -P "your-password"
To subscribe using the secured listener on port 8883, do the following:
- mosquitto_sub -h mqtt.example.com -t test -p 8883 --capath /etc/ssl/certs/ -u "your-username" -P "your-password"
And this is how you publish to the secured listener:
- mosquitto_pub -h mqtt.example.com -t test -m "hello world" -p 8883 --capath /etc/ssl/certs/ -u "your-username" -P "your-password"
Note that we're using the full hostname instead of
localhost. Because our SSL certificate is issued for
mqtt.example.com, if we attempt a secure connection to
localhost we'll get an error saying the hostname does not match the certificate hostname.
- Host is the domain for your Mosquitto server,
- Port is
- ClientId can be left to the default randomized value
- Path can be left to the default value of /ws
- Username is your Mosquitto username from Step 3
- Password is the password you chose in Step 3
The remaining fields can be left to their default values.
After pressing Connect, the client will connect to your server. You can publish and subscribe using the Subscribe and Publish Message panes below the Connection pane.
We've now set up and tested a secure, password-protected and SSL-encrypted MQTT server. This can serve as a robust and secure messaging platform for your IoT, home automation, or other projects.