Mosquitto is an open-source message broker, which means it allows different programs to exchange information in a way they can all understand.
Information is exchanged via channels, where you publish information or subscribe to to receive information.
For example, you could have a channel for every sensor in house, organised by room:
The Raspberry Pi, receiving information from various places, puts that information on the right channel so home automation software like OpenHAB can pick it up.
/FirstFloor/Living/Temperature /FirstFloor/Living/Humidity /FirstFloor/Kitchen/Temperature etc.
First get the repository package signing key, import it into apt, and remove the key file again:
wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key sudo apt-key add mosquitto-repo.gpg.key rm mosquitto-repo.gpg.key
Then make the mosquitto repository available to apt:
cd /etc/apt/sources.list.d/ sudo wget http://repo.mosquitto.org/debian/mosquitto-wheezy.list sudo apt-get update
Now we can install the core packages (server & clients):
sudo apt-get install mosquitto mosquitto-clients
Mosquitto is automatically started as soon as it's installed. To test, open a second terminal tab (you can do this as an extra tab in the same MobaXterm window).
Make Terminal 1 listen on the hello/world channel ("-d" means to output debug information, "-t" followed by a channel name specifies the channel):
mosquitto_sub -d -t hello/world
Have Terminal 2 publish something on the hello/world channel (same options as when subscribing, plus "-m" followed by a message):
mosquitto_pub -d -t hello/world -m "Greetings from Terminal window 2"
If all goes well, you should see the message appear in Terminal 1.
Now we'll hook the RF24 modules up to the Pi and Arduino so they can talk to each other!RF24