Raspberry Pi 2 Error accessing GPIO with SUDO for AdafruitDHT and AM2302/DHT22 sensor

Question

I've built my Raspberry Pi2 with Unbuntu per the instructions here. Software wise I have installed the following packages

• python-pip
• python-dev
• mercurial

as well as the following python packages

• Raspberry Pi GPIO;

  sudo pip install hg+http://hg.code.sf.net/p/raspberry-gpio-python/code#egg=RPi.GPIO
  

• Adafruit DHT

  git clone https://github.com/adafruit/Adafruit_Python_DHT.git
  cd Adafruit_Python_DHT
  sudo python setup.py install
  

When I try to run the Adafruit_Python_DHT/examples/simpletest.py I use the following command. I did have to update the pin# in the script to match the pin that I used when I hooked it up.

sudo python simpletest.py

The response I get from it this is:

Traceback (most recent call last):   
File "simpletest.py", line 40, in <module> humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)   File "build/bdist.linux-armv7l/egg/Adafruit_DHT/common.py", line 90, in read_retry   
File "build/bdist.linux-armv7l/egg/Adafruit_DHT/common.py", line 77, in read   
File "build/bdist.linux-armv7l/egg/Adafruit_DHT/Raspberry_Pi_2.py", line 34, in read RuntimeError: Error accessing GPIO. 
Make sure program is run as root with sudo!

So I did some research and I found some information regarding the use of the /dev/mem but I did not quite feel that this applied to my build although this is where I found a solution to install the dev version of the GPIO lib instead of the version that gets pulled from the OS repo. In my research on Adafruit's site it was clear that the library is supported on Raspbian. So I rebuilt the Pi using Raspbian and performed the same test without having to install the GPIO library and it worked fine.

So now I am stumped. I would really like to use Ubuntu as my OS for the Pi but at the same time need to be able to leverage this and presumably other similar libraries.

Answer 1

The RPi.GPIO Python module is bundled with Raspbian.

Currently RPi.GPIO has to be run with root priviliges because it accesses /dev/mem. You need root priviliges to access /dev/mem.

So you have to run RPi.GPIO with sudo or similar.

Shortly RPi.GPIO may be changed to use /dev/gpiomem rather than /dev/mem. If that happens members of group gpio should be able to run RPi.GPIO without root priviliges.

Answer 2

I got the DHT22 sensor working in a similar setup (Ubuntu community maintained on RPi 2) by "adding Device Tree support to the kernel" by following the detailed steps provided by poster "KTB" in this thread: https://www.raspberrypi.org/forums/viewtopic.php?t=113014&p=773725