snapcrafters/arduino

cannot open device: Permission denied

Closed this issue · 4 comments

mmartinortiz commented

Hi,

Before opening this issue, I've read the "Readme" in the Snap Store and search in the Internet to see how to fix it. I'm running:

  • Ubuntu 20.04

  • Arduino IDE 1.8.13

  • Installed the Arduino IDE via the Ubuntu Software as Snap. I've checked the permissions of the Snap, all are enabled. Access serial port hardware drop down list only shows (disconnected)

  • Added my user to the dialout group.

  • Computer rebooted (several times). When I run the command groups I get myuser adm dialout cdrom sudo dip plugdev lpadmin lxd sambashare docker

  • Followed the steps to install my Arduino board (Arduino Uno Wifi rev2). Instructions detailed here

At the end, I reached to this comment. I've checked the udev rules created by the Snap, I see that the file is auto-generated, and I'm not sure how to modify it.

When I try to run a program, the output is:

Arduino: 1.8.13 (Linux), Board: "Arduino Uno WiFi Rev2, ATMEGA328"

Sketch uses 1970 bytes (4%) of program storage space. Maximum is 48640 bytes.
Global variables use 28 bytes (0%) of dynamic memory, leaving 6116 bytes for local variables. Maximum is 6144 bytes.
An error occurred while uploading the sketch
avrdude: usbdev_open(): cannot open device: Permission denied
avrdude: jtag3_open_common(): Did not find any device matching VID 0x03eb and PID list: 0x2145

Permissions of the device:

> ls -l /dev/ttyACM0
crw-rw---- 1 root dialout 166, 0 oct 24 17:47 /dev/ttyACM0

If I open the Serial Monitor, I can see the logs of the program that currently runs in the Arduino board.

If this is an issue with the udev rules, how can I help to debug it?

PD: In the past I used this board in the same laptop. It was with an instance of Ubuntu 18.04. Back then I installed the Arduino IDE from the official package at the Arduino site. I remember that I also had issues, but I did not find the notes I took to fix them.

merlijn-sebrechts commented

Thanks for this detailed issue, @mmartinortiz!

The permission "Access USB hardware directly" gives Arduino access to the board if your user account already has access. I think the issue is that your user account does not yet have access.

I do not have this board so I need your help to test a fix. I wrote this based on the comment you linked

Run these two commands in a regular terminal as your user.

echo "SUBSYSTEM==\"usb\", MODE=\"0660\", GROUP=\"$(id -gn)\"" | sudo tee /etc/udev/rules.d/00-usb-permissions.rules
udevadm control --reload-rules

After you run this, try to run the program again.

  • 👍1
mmartinortiz commented

That did the trick :-)

Is this an issue related to my user (local installation) or my board? And could we modify the snap to add this rule?

In any case, thank you very much.

merlijn-sebrechts commented

Is this an issue related to my user (local installation) or my board?

This is an issue related to the board and the plugin for the board. Most plugins access boards using a standardized usb-serial protocol. By adding your user to the dailout group, your give it permission to use this protocol. That is part of the regular installation instructions.

The plugin of your board, however, accesses the USB interface directly. It does not use this standardized protocol. This direct access is normally only allowed by the root user because it is potentially dangerous and insecure. With the lines I pasted, you give your user unrestricted access to all raw USB interfaces.

And could we modify the snap to add this rule?

Snaps are not permitted to add these rules because these rules change the security of your operating system. Users always have to add these rules themselves. Even if the snap could do it, I would not add it because it makes your system less secure and it is only needed for a very small number of boards.

What I will do is to add this information to the description of the snap, so that users who have this issue can more easily find the solution.

The way to permanently solve this issue is to convince the developers of the board and the plugin to use the standardized usb-serial protocol instead of accessing the raw usb device.

mmartinortiz commented

Thanks for such a good explanation. Now it is clear to me, I created a pull request for adding this information to the Snap description.