mosquitto

mosquitto is an Open Source MQTT server. MQTT is a machine to machine or IOT (Internet of Things) protocol.

https://mosquitto.org

To install run

apt-get install mosquitto mosquitto-clients

To test, run

mosquitto_sub -h localhost -t test

To create a user, run

mosquitto_passwd -c /etc/mosquitto/passwd USER_NAME

Config file available at

/etc/mosquitto/conf.d/default.conf

To restart, use

systemctl restart mosquitto

To connect with user and password, use

mosquitto_sub -h localhost -t test -u "USER_NAME" -P "PASSWORD"