/dev/ttyACM0: permission denied on openSUSE

I am trying to use an “Arduboy,” based on the Arduino Leonardo, with the Arduino IDE. I cannot upload the example code, however, because of the following error:

avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied
Problem uploading to board.  See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

Before you mark this as a duplicate, here are all of the things I have tried

• Adding myself to the dialout group that /dev/ttyACM0 can be modified by
• Running chmod a+rw /dev/ttyACM0 every time I plug in the board
• Making this udev rule: KERNEL=="ttyACM0", MODE="0666"

None of these things worked. What did work was running it with xdg-su like so: xdg-su -c ./arduino. However, I think it’s not the best idea to run the thing as root every time. Is there anything I can do?

I am running openSUSE Tumbleweed.

Answer

The Arduino Leonardo based boards interrupt the communication with ttyACM* for a short moment (like logging in and out) during an upload. For some reason, the permissions change during this process. See the output of a repeated ls -l --full-time /dev/ttyACM0 during a failed upload:

crw-rw-rw- 1 root dialout 166, 0 2019-08-11 17:28:31.974025089 +0200 /dev/ttyACM0
ls: cannot access '/dev/ttyACM0': No such file or directory
crw------- 1 root root 166, 0 2019-08-11 17:42:15.523439213 +0200 /dev/ttyACM0
crw-rw---- 1 root dialout 166, 0 2019-08-11 17:42:16.083442857 +0200 /dev/ttyACM0

I also use Tumbleweed. The only workaround that I currently know is to start the Arduino IDE as root.