How do I make libusb work as non-root?

It's still not the "muggle's tweak" that I'm really looking for, but at least this works:

Apparently there are two directories for udev (I have no idea why):

• /etc/udev/rules.d
• /lib/udev/rules.d

I'd been messing with the /lib one and getting nowhere. I found the /etc one here, and it does work:

---

Put SUBSYSTEM=="usb", ATTRS{idVendor}=="VID", ATTRS{idProduct}=="PID", MODE="0666"

• VID is the USB-IF-assigned Vendor ID of the device in question *

• PID is the Vendor-assigned Product ID of the device in question *

• 0666 gives universal read/write access to whatever matches this line

  * _{$ lsusb to see all attached USB devices and their ID's.}

In /etc/udev/rules.d/xx-my-rule.rules (may need root/sudo permissions)

• xx is any number > 50 (the defaults are in 50, and higher numbers take priority)
• my-rule is whatever you want to call it
• must end in .rules

Then udevadm control --reload-rules (may also need root/sudo permissions), and it should "just work" for that specific VID/PID pair.

---

Another option, to tighten the permissions a little bit more, is to use TAG+="uaccess" in place of MODE="0666". This limits access to the currently-logged-in (physical) user instead of all users. Thanks @Lekensteyn!

For anyone else struggling with this - i needed to add GROUP="plugdev" to my udev rule under Ubuntu 18.04 to make it work.

so for my BTD-400 adapter the file /etc/udev/rules.d/51-usb-device.rules reads:

SUBSYSTEM=="usb", ATTRS{idVendor}=="0a5c", ATTRS{idProduct}=="21e8", GROUP="plugdev", TAG+="uaccess"