I have a Flask setup in my Raspberry Pi 4 Model B via this tutorial.
OS = Ubuntu Server 20.04.2 LTS
Python = 3.8
Please keep in mind that I am using virtual env for my Flask application as shown in the tutorial and my Flask application is running absolutely fine.
Now I installed Adafruit_DHT in the same venv and tried using the following code in one of the endpoints
import Adafruit_DHT
humidity, temperature = Adafruit_DHT.read_retry(Adafruit_DHT.DHT22, 24)
to which I am getting the following error
File "/usr/local/lib/python3.8/dist-packages/Adafruit_DHT/common.py", line 81, in read
return platform.read(sensor, pin)
File "/usr/local/lib/python3.8/dist-packages/Adafruit_DHT/Raspberry_Pi_2.py", line 34, in read
raise RuntimeError('Error accessing GPIO.')
RuntimeError: Error accessing GPIO.
So, after that, I created a simple python script say z.py and wrote the above code in it. Then, I activated the same Flask venv using
source venv1/bin/activate
And run the script using
python z.py
Again I got the same error. But If I run the above command as sudo
sudo python z.py
then script executed perfectly fine and I got the following response
87.0999984741211 29.399999618530273
So, now the question arrives, how do I use Adafruit_DHT package inside the Flask app with sudo permission?
I don't think setting 777 to www-data group would be the right choice. Or running the Flask app as sudo user would be a great idea.
I have tried installing Adafruit_DHT package globally with sudo, but still I have to execute z.py as sudo
So what is the correct way to do this?
I believe the package will be trying to access the device /dev/gpiomem (possibly (/dev/gpiochip0 or /dev/gpiochip1).
I think the neatest way to address this would be have those devices be owned by a group other than root and give that group permission to access the device, e.g.
sudo su
groupadd gpio
chgrp gpio /dev/gpio*
chmod g+rw /dev/gpio*
Then I'd go ahead and add your user to that group (by default this is ubuntu, but you may have created another user):
usermod -a -G gpio ubuntu
Now you've created a group called "gpio" that now has permissions to access your Pi's GPIO, and added your user to that group.
Please note, I have not tested this
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