M. N.

Hi Ben, with Ubuntu 20.04 on RPi 4, the message is now more descriptive: Traceback (most recent call last): File "<stdin>", line 1, in <module> RuntimeError: No access to /dev/mem. Try running as root! When running as root or after changing the permissions (see my comment above) GPIO seems to work OK. The remaining source of confusion might be that /dev/mem doesn't actually exist on my system. RPi.GPIO only complains about it because it's what was used as a fallback, but the underlying issue are...

Got the same problem with Ubuntu 20.04 on RPi 4. Resolved it by creating a "gpio" group, and adding an udev rule to give this group access to "/dev/gpiomem" (normally can only be accessed by root). Create /etc/udev/rules.d/90-gpio.rules with: KERNEL=="gpiomem", OWNER="root", GROUP="gpio" Create the group itself and assign it to an existing user "pi": sudo groupadd -f --system gpio sudo usermod -a -G gpio pi "/dev/gpiomem" should be writeable on the next boot.