Configure udev to change permissions on USB HID device?
I have a USB scale, a USB HID. Currently, when it is plugged in, the permissions only allow the superuser to access it. How can I configure udev to let anybody access this device? I have the vendor and product IDs, but I would like to match it based on the HID type instead.
Right now, I’m having trouble finding any existing rule that applies to this (I grepped for “hidraw” in /lib/udev/rules.d and /etc/udev/rules.d, among other things).
Normally, this is done by adding to /etc/udev/rules.d a file maybe named 50-usb-scale.conf with contents like this:
SUBSYSTEM=="usb", ATTR{idVendor}=="HEX1", ATTR{idProduct}=="HEX2", MODE="0666"
Where HEX1 and HEX2 are replaced with the vendor and product id respectively.
To match on the Interface type instead, you could try replacing ATTR{idVendor}=="HEX1", ATTR{idProduct}=="HEX2" with a match for bInterfaceClass being 03 (HID):
SUBSYSTEM=="usb", ATTR{bInterfaceClass}=="03", MODE="0666"
But be warned, that will catch mice and keyboards too.
In case you need to change (like me) ttyACM0 permissions,
this are my settings:
KERNEL=="ttyACM0", MODE="0777"
It failed when I tried to specify the vendor and product ID. I am not sure why.
If its a HIDRAW device, you have to
chmod 0666 /dev/hidrawX
where X is the hid device number, e.g hidraw0. you can do
ls /dev/hid*
to see a list 🙂
Or just do
sudo chmod 0666 /dev/hidraw*
to set for all hidraw devices, probably not recommended.
Just for the summary:
You may filter for:
- idVendor
- idProduct
- serial
And use:
== Compare for equality.
!= Compare for inequality.
= Assign a value to a key. Keys that represent a list are reset and only this single value is assigned.
+= Add the value to a key that holds a list of entries.
:= Assign a value to a key finally; disallow any later changes.
You may give a specific device a specific new path in /dev/…
Example:
KERNEL=="hiddev*", ATTRS{idVendor}=="16c0", ATTRS{idProduct}=="05df", ATTRS{serial}=="1234567", GROUP="cdrom", OWNER="user28", MODE="0640", SYMLINK+="myhid"
Results in:
You can access the device via ‘/dev/hiddevx’ or via ‘/dev/myhid’ easyly, every user in group ‘cdrom’ may read from the device. Owner ‘user28’ may read and write.
or simplest:
KERNEL=="hiddev*", ATTRS{idVendor}=="16c0", MODE="0666"
Results in:
Every user may access every hiddevice from Vendor 0x16c0
For details see: Docs
Ubuntu 18.04 update/clarification:
Kees Cook’s answer is close but requires 2 changes to work in 18.04 (the current release and only one I’ve tested this on).
- Find your idVendor and idProduct with lsusb.
- This will be the 2 hex values after “ID”, separated by a colon. I’m adding a scanner. lsusb gave me:
Bus 001 Device 011: ID 04b8:014a Seiko Epson Corp.
- This will be the 2 hex values after “ID”, separated by a colon. I’m adding a scanner. lsusb gave me:
- As root add a file to /etc/udev/rules.d
- Something like 50-usb-epsonscanner.rules
- The extension must be “.rules”
- In that file add:
SUBSYSTEM=="usb", ATTRS{idVendor}=="04b8", ATTR{idProduct}=="014a", MODE="0666"But with your idVendor and idProduct hex values.
- Note it’s “ATTRS” not “ATTR”.
- Re-login. No need to reboot.
For a USB tty device, I needed to do:
SUBSYSTEM=="tty", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", MODE="0666", GROUP="bkg"
The accepted answer was good – but needed the SUBSYSTEM to be tty
The thing that helped be debug, was to be able to see what UDEV was doing by doing a:
udevadm test $(udevadm info -q path -n /dev/ttyUSB0)