Document how to deal with FILE_ERROR_ACCESS_DENIED in Linux

[agustinmista]

Some Linux builds of Chromium and friends are often prone to not being able to open serial devices that by default belong to root. The recommended way to solve this is to add a udev rule overriding their mode to something more open like 0666.

For instance, adding the following to /etc/udev.d/99-heltec-v3.rules did the trick for me:

# Silicon Labs CP210x UART Bridge (Heltec V3)
SUBSYSTEM=="tty" ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", MODE="0666"

The specific values for the vendor and product ID will depend on the particular device being flashed. After that, one can reload the rules by running sudo udevadm trigger or by re-plugging the device.

I think this could be documented somewhere. Maybe in a small "troubleshooting" drop down near the flash button? 😄

[kquinsland]

For completeness, the location for udev rules will differ based on distro.

In any case, I have a variety of CP210x and CH340 based devices:

❯ cat /etc/udev/rules.d/99-heltec-v3.rules
# See: https://github.com/meshtastic/web-flasher/issues/266
##
# Silicon Labs CP210x UART Bridge (Heltec V3)
SUBSYSTEM=="tty" ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", MODE="0666"

# CH340 based devices (like LILYGO T-Beam). Note that the product ID may vary. Use `*` at your peril!
SUBSYSTEM=="tty" ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="55d4", MODE="0666"

That will make it so anybody on the computer has access to them (0666). This may not be what you want / may wish to restrict access to members of the group input or similar:

❯ cat /etc/udev/rules.d/99-heltec-v3.rules
# <...>
SUBSYSTEM=="tty", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="55d4", MODE="0660", GROUP="input", TAG+="uaccess", TAG+="udev-acl"

or similar.

In any case, the rules can be reloaded and applied immediately with:

❯ sudo udevadm control --reload-rules && sudo udevadm trigger