1. Install Mosquitto
sudo apt-get install mosquitto -y
sudo apt-get install mosquitto-clients

2. Configure Mosquitto.
a. Run the following
sudo nano /etc/mosquitto/mosquitto.conf

b. Paste the following:
# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example

pid_file /var/run/mosquitto.pid

persistence true
persistence_location /var/lib/mosquitto/

log_dest file /var/log/mosquitto/mosquitto.log

allow_anonymous false
password_file /etc/mosquitto/pwfile
listener 1883

3. Setup Mosquitto credentials
sudo mosquitto_passwd -c /etc/mosquitto/pwfile TYPE_YOUR_USERNAME_HERE

4. Test the Mosquitto by subscribing to a topic
mosquitto_sub -d -u MOSQUITTO_USERNAME -P MOSQUITTO_PASSWORD -t dev/test