oh udev. oh yes

I try and do the “right thing” when it comes to the future and how linux distros see their roles and the way things should be.  I think systemd has some generally good ideas, though I think upstart has far far better documentation.  Anyway, given that linux distros still “protect” users from plugging in usb devices, except for all those ones that they _don’t_ protect you from, if you’re working with embedded electronics, sooner or later you need to “fix” permissions for some device you have.  No matter, the canonical advice for a “long time” has been something like adding a file in /etc/udev/rules.d/doesnt_really_matter.rules with some content like…

ATTRS{idVendor}=="aaaa", ATTRS{idProduct}=="bbbb", GROUP="plugdev"

And you added yourself to the plugdev group, and everything was pretty much ok. Now, it’s the “future” and we can’t use anything so silly and outdated as groups to assign permissions. Heaven help us, what would become of us all if people just used groups?! Now we need to use “tags” and a magical “uaccess” incantation. Except for all those devices that we do use groups for, like usb modems, usb serial ports, usb printers, wireshark capture permissions, virtualization, colour correction devices, basically everything except “unknown” devices.

But ok, good and well, we’ll learn the new magic incantation for udev….

ATTRS{idVendor}=="aaaa", ATTRS{idProduct}=="bbbb", TAGS+="uaccess"

And…. it doesn’t work. Why? Good fucking luck finding out. If you’re lucky, someone might suggest that the name of your file isn’t right. Why should that matter? Welllll. because it does. See https://lists.freedesktop.org/archives/systemd-devel/2015-August/033946.html and https://bugzilla.redhat.com/show_bug.cgi?id=1074122#c0 for some hints and clues.

TL;DR: pretty much must be named 70-doesnt-matter.rules. At least until system decides that it should be a different number without documenting it anywhere.

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