The sys admin's daily grind – Mosquitto

No Insect Bites

Article from Issue 198/2017

Sys admin Charly does not tend toward hostilities, but he has huge problems with mosquitoes. Despite this, he does make an exception for the Mosquitto message broker.

I recently read that around 100 species become extinct every year. So why not mosquitoes? I am merciless on the issue, because I happen to be allergic to their stings. I can't sleep, with just one of these pests buzzing around my bedroom. My weapon of choice – always at hand to decimate the population of my enemy – is a 30-year-old school atlas beside the bed. But it is still a Sisyphean task.

And the bloodstains on the wallpaper also impact on the kind of atmosphere that I would like have in my bedroom, which explains why I repaper the walls nearly every year. I also failed to secure a majority vote in the family council for my suggestions of adopting mosquito-eating spiders or using a Linux and LiDAR (light detection and ranging) based mosquito laser. War is always miserable.

You will thus understand that my response to a piece of software named after these flying bloodsuckers was somewhat skeptical. However, this much I will reveal in advance, Mosquitto [1] is allowed to stay. The tool was given its name, because the developer wanted to have the letters MQTT in there somewhere, as the acronym for message queue telemetry transport. And telemetry is the right keyword for describing Mosquitto's task.

Mosquitto operates a messaging hub; in MQTT speak, this is known as the message broker. Any client wanting to communicate sends its message to the broker (publisher), and all clients that have a subscription with the broker (subscribers) then receive the message. The broker is simply named mosquitto and runs as a daemon; the clients that publish and subscribe go by the names of mosquitto_pub and mosquitto_sub.

First, I start the broker. It normally runs in the background, but I can also stop the daemon and start it in the foreground on the console. Because Mosquitto runs on port 1883, I don't even need root privileges to do this:

mosquitto -v

The -v parameter sets a higher verbosity level, so that I can send to the broker at work. Then I use the mosquitto_sub client to subscribe to a topic. The topic is freely selectable and should ideally describe the type of data that you can expect in a meaningful way. As an example, I can subscribe to the topic date:

mosquitto_sub -h -i subscriber -t date

The -i parameter describes the client's identity and is freely definable. I used subscriber here; in a practical application, however, it would make more sense to use the client's hostname.

Mosquitto News

Time to publish something. On another console, I typed the following:

mosquitto_pub -h -i publisher -t date -m "30.02.2017 ;-)"

See Figure 1. The text passed in with -m <text> immediately appears on the console where mosquitto_sub is waiting for data.

Figure 1: In the upper console, a client is sending a message to another client – the console at the bottom receives it immediately.

Impressively simple, don't you think? In daily use, topics are often hierarchically organized; users separate the hierarchy levels with a slash, as in: readings/humidity/outdoor. You can secure communication with TLS and also stipulate that the server and clients identify themselves with certificates. I must admit: Mosquitto is useful. But my atlas is still staying where it is!


  1. Mosquitto:

The Author

Charly Kühnast manages Unix systems in the data center in the Lower Rhine region of Germany. His responsibilities include ensuring the security and availability of firewalls and the DMZ.

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Home Assistant with MQTT

    Automating your four walls does not necessarily require commercial solutions. With a little skill, you can develop your own projects on a low budget.

  • WiFi Thermo-Hygrometer

    A WiFi sensor monitors indoor humidity and temperature and a Node-RED dashboard reports the results, helping you to maintain a pleasant environment.

  • Controlling a Smart Plug

    You could spend hundreds of dollars on specialized IoT appliances and fixtures, or you could just hack a smart plug and talk to it with your Linux system.

  • ESPHome

    With an ESP32 or Raspberry Pi Pico W microcontroller board, you can easily create your own home automation devices. Thanks to ESPHome, you don't even have to be a programmer.

  • Safe Messaging with TLSA

    Decoupled application design gets in the way of secure communication, but a little known feature of DNS can provide message security.

comments powered by Disqus
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters

Support Our Work

Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

Learn More