Low voltage. Mostly harmless...

Raspberry Pi as a MQTT server

Jul 13, 2017
4 minute read

With a price tag of 10$, a form-factor of a business card, power usage under 1 Watt and yet an 1GHz CPU and built-in WiFi, the Raspberry Pi Zero W makes for a great platform for experiments with Linux, networking, software development and tinkering in general. This is a step-by-step guide on how to install Raspbian on a headless Raspberry Pi Zero W, configure a couple of system services and setup a mosquitto MQTT server. Some of the steps are mostly for convenience and are optional.

Required hardware

  • Raspberry Pi Zero W (Wireless)
  • microSD card, 4Gb or more
  • A 5V power adapter and a micro USB cable

Install a Raspberry Pi image

Download the “Raspbian Jessie Lite” image from https://www.raspberrypi.org/downloads/raspbian/ and install it on a micro-SD card. This is a slimmed-down distribution for headless installations and comes with no graphical UI.

Setup WiFi network access

With the SD card still connected to your computer, open the newly created “boot” drive / partition. Its size should be about 40Mb. Create a wpa_supplicant.conf file and fill-in your WiFi credentials:

network={
       ssid="NetworkSSID"
       psk="NetworkPassphrase"
       key_mgmt=WPA-PSK
    }

If the Raspberry Pi will be used on multiple networks, all of them can be listed:

network={
       ssid="Home NetworkSSID"
       psk="Home NetworkPassphrase"
       key_mgmt=WPA-PSK
    }

network={
       ssid="Office NetworkSSID"
       psk="Office NetworkPassphrase"
       key_mgmt=WPA-PSK
    }

Enable SSH access

Create a file on the “boot” partition named ssh (no extension)

Power on the Raspberry Pi

Plug in the SD card and connect the power cable. There will be a minute or so of initial activity. If everything works fine, the Pi should receive a dynamic IP address from your network’s router.

Assign a static IP

In your router’s web interface, check for a “raspberrypi” DHCP client and assign a fixed (static) IP address to it. Let’s say this IP is 192.168.0.60.

Add the Pi’s static IP to your computer’s hosts file

This is /etc/hosts for Linux and %SystemRoot%\System32\drivers\etc\hosts on most Windows. Add a new line in ip hostname format, for example:

192.168.0.60   pizero

This allows a more friendly name “pizero” to be used for all access to the Raspberry Pi (Web, SSH, MQTT, etc) instead of the numeric IP.

SSH to the Pi

On every Raspbian installation, there’s a default user pi with password raspberry. Run ssh pi@192.168.0.60 on the command line and input the password.

Install utility packages

This is the time to install your favorite tools. vim is my editor of choice and will be used in all edit commands below.

$ sudo apt-get install -y vim htop

Change the hostname

Use a text editor to change the default host name “raspberrypi” in the following two files:

$ sudo vim /etc/hostname
$ sudo vim /etc/hosts

These changes need a restart to get in effect:

$ sudo reboot

Add your public SSH key

There are a couple of ways to transfer your SSH public key to the Raspberry:

1. Copy-paste:

Copy the contents of id_rsa.pub to the clipboard. The on the Pi’s command line:

$ mkdir .ssh
$ cat >> ~/.ssh/authorized_keys
(Paste from clipboard)
(Press Ctrl+D)

2. Download from GitHub

If your public key is already on GitHub, it’s a one-line command to get it in place:

$ mkdir .ssh
$ curl https://github.com/<username>.keys | tee -a ~/.ssh/authorized_keys

Logout and login into the Pi again to test the key-based authentication. There should be no prompt for a password.

Tighten up security

Pi’s default username and password are an obvious security risk, but with SSH access enabled we can safely disable password-based authentication.

$ sudo vim /etc/ssh/sshd_config

change the following settings to “no”:

# Authentication:
...
PermitRootLogin no

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no

and append a line at the bottom of the file:

AddressFamily inet

Finally, restart the ssh service

$ sudo service ssh restart

Reduce power usage

In a headless setup the HDMI port is not used, so it can be disabled to save a few milliamps of power:

$ sudo vim /etc/rc.local

and add a line before “exit 0”:

/usr/bin/tvservice -o

It’s also possible to disable the status LED

Install mosquitto

Both the mosquitto server and the mosquitto_sub & mosquitto_pub command-line utilities can be installed from the default repositories:

$ sudo apt-get install -y mosquitto mosquitto-clients

The server starts automatically and we can check its status with:

$ sudo service mosquitto status

● mosquitto.service - LSB: mosquitto MQTT v3.1 message broker
   Loaded: loaded (/etc/init.d/mosquitto)
   Active: active (running) since Thu 2017-07-13 20:35:15 UTC; 2min 40s ago
   CGroup: /system.slice/mosquitto.service
           └─5547 /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf

Jul 13 20:35:15 pizero mosquitto[5542]: Starting network daemon:: mosquitto.
Jul 13 20:35:15 pizero systemd[1]: Started LSB: mosquitto MQTT v3.1 message broker.

To test the command-line tools we need two terminals open:

(In terminal 1)
$ mosquitto_sub -t "test/topic" -v

(In terminal 2)
$ mosquitto_pub -t "test/topic" -m "Hello, world"

The “Hello, world” message is published to the “test/topic” MQTT topic in terminal 2 and is received and printed in terminal 1.

mosquitto cheatsheet

Config file location:  /etc/mosquitto/mosquitto.conf
Log file location:     /var/log/mosquitto/mosquitto.log
Service file location: /etc/init.d/mosquitto

Check server status:        sudo service mosquitto status
Start/stop/restart server:  sudo service mosquitto [start|stop|restart]

Command-line options for "mosquitto_sub" and "mosquitto_pub":
       -h     hostname, defaults to "localhost"
       -t     topic name
       -m     text message
       -v     verbose mode

Resources

  • https://raspberrypi.stackexchange.com/questions/62933/set-up-a-raspberry-pi-zero-w-without-monitor-or-ethernet-module
  • https://mattwilcox.net/web-development/setting-up-a-secure-home-web-server-with-raspberry-pi
  • https://www.linode.com/docs/security/securing-your-server/
  • https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
  • https://www.jeffgeerling.com/blogs/jeff-geerling/raspberry-pi-zero-conserve-energy
  • https://www.digitalocean.com/community/tutorials/how-to-install-and-secure-the-mosquitto-mqtt-messaging-broker-on-ubuntu-16-04