#RaspberryPi – Putting all together to display device temperature using #AzureIoT and #docker. Privilege permissions and other lessons learned

Hi!

Today challenge was based on an easy one

How do I get a Raspberry Pi temperature using Python?

The lines to do this are quite simple, with the following lines we can get the absolute value for the device temperature, in Celsius (of course!)

	import os
	def getCPUtemperature():
	res = os.popen('vcgencmd measure_temp').readline()
	return(res.replace("temp=","").replace("'C\n",""))
	print(getCPUtemperature())

view raw RaspberryPiGetDeviceTemp.py hosted with ❤ by GitHub

Easy! My next step was to add a new [Device Property] to my [Device Template] in Azure IoT. I’ll store this as a temp string, so this is fine.

The lines to send the temperature as a device property are part of the following code sample. I also track the temperature as telemetry so I can work with the history of the device temp

	import os
	import iotc
	def getCPUtemperature():
	res = os.popen('vcgencmd measure_temp').readline()
	return(res.replace("temp=","").replace("'C\n",""))
	def sendTempAndConnectionDate():
	print("Sending temp and connection date ..")
	propJson = "{\"rpiTemp\": \"" + str(getCPUtemperature()) + "\"}"
	iotc.sendProperty(propJson)
	telemetryMessage = "{\"temp\": " + str(getCPUtemperature()) + "}"
	iotc.sendTelemetry(telemetryMessage)

view raw AzureIoTCSendDeviceProperty.py hosted with ❤ by GitHub

So far, so good!

Now it was time to package all this in a docker image and run it from a container. I got an ugly surprise when I realize that I got an exception trying to get the device temperature

VCHI Initialization failed

Time to read and learn more about docker and containers on Raspberry Pi.

In the official documentation of [Docker Run, see references] I found a couple of options which may help me. There are 2 options to allow me access to the device temperature

• Run the container with the specific path to the device I want to grant privileged access for my container
• Run the container with the [–privileged] argument to enable access to all devices on the host

Of course, the 2^nd one is easier, but much more dangerous

When the operator executes docker run –privileged, Docker will enable access to all devices on the host as well as set some configuration in AppArmor or SELinux to allow the container nearly all the same access to the host as processes running outside containers on the host. Additional information about running with –privileged is available on the Docker Blog.

I didn’t think twice and run my image with the [–privileged] argument.

sudo docker run --privileged -p 80:80 <Image ID>

And now I can get an amazing history and track of information using docker, containers and Azure IoT with a Raspberry Pi

Happy coding!

References

• Docker Run, https://docs.docker.com/engine/reference/run/
• El Bruno, How to install .Net Core in a Raspberry Pi 4 and test with HelloWorld https://elbruno.com/2019/08/27/raspberrypi-how-to-install-dotnetcore-in-a-raspberrypi4-and-test-with-helloworld-of-course/
• El Bruno, Installing Visual Studio Code in a Raspberry Pi https://elbruno.com/2019/08/20/vscode-installing-visual-studio-code-in-a-raspberrypi-a-couple-of-lessons-learned-code/
• El Bruno, Build and Run C# ,NetCore projects in a Raspberry Pi 4 with Visual Studio Code https://elbruno.com/2019/08/28/vscode-build-and-run-c-dotnetcore-projects-in-raspberrypi/
• Let’s do some Git dev in Raspberry Pi 4 (GitHub and Azure DevOps!) https://elbruno.com/2019/09/02/vscode-lets-do-some-git-dev-in-raspberrypi-github-and-azure-devops/
• How to install Docker in a Raspberry Pi 4 https://elbruno.com/2019/09/17/vscode-how-to-install-docker-in-a-raspberrypi-4/
• Where is my Task Manager? let’s try htop https://elbruno.com/2019/09/23/raspberrypi-where-is-my-task-manager-lets-try-htop/
• Sending custom Telemetry and Event information from a Raspberry Pi device to Azure IoT Central https://elbruno.com/2019/09/18/azure-sending-custom-telemetry-and-event-information-from-a-raspberrypi-device-to-azureiot-central/