No access to /dev/mem

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npavel
 
Posts: 3
Joined: Mon Apr 10, 2023 10:20 am

No access to /dev/mem

Post by npavel »

My setup is RasPi 4, Ubuntu 20 with BME280 connected by SPI. I am trying to execute the following example code:
import board
import digitalio
from adafruit_bme280 import basic as adafruit_bme280
spi = board.SPI()
cs = digitalio.DigitalInOut(board.D5)
bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, cs)

and I receive the following error:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/pi/.local/lib/python3.8/site-packages/digitalio.py", line 165, in __init__
self.direction = Direction.INPUT
File "/home/pi/.local/lib/python3.8/site-packages/digitalio.py", line 195, in direction
self._pin.init(mode=Pin.IN)
File "/home/pi/.local/lib/python3.8/site-packages/adafruit_blinka/microcontroller/bcm283x/pin.py", line 40, in init
GPIO.setup(self.id, GPIO.IN)
RuntimeError: No access to /dev/mem. Try running as root!

The user is member of kmem, gpio, spi groups. I tried lowering kernel.yama.ptrace_scope to 0. Checked AA rules as well.
Any idea what could be done instead of going the sudo way?

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mikeysklar
 
Posts: 13936
Joined: Mon Aug 01, 2016 8:10 pm

Re: No access to /dev/mem

Post by mikeysklar »

I assume everything runs correctly with sudo?

If so, it is probably just a simple permission change on /dev/mem.

Code: Select all

sudo chown root.gpio /dev/mem
sudo chmod g+rw /dev/mem

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npavel
 
Posts: 3
Joined: Mon Apr 10, 2023 10:20 am

Re: No access to /dev/mem

Post by npavel »

Thank you for your suggestion. I tried this:
crw-rw---- 1 root gpio 1, 1 Apr 21 2022 /dev/mem

Unfortunately the result is the same error.

When run as root, I don't see this error. But then I have different issue, because Python can't find the adafruit_bme280 module. While I can solve this on a user level with exportpath, I can't solve it as sudo. I tried with site-packages in /usr/lib/python, but to no avail.

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npavel
 
Posts: 3
Joined: Mon Apr 10, 2023 10:20 am

Re: No access to /dev/mem

Post by npavel »


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