faq_udev.md

Rules for udev & permissions for devices HOWTO

This note should be applicable to any modern GNU/Linux distro.

Basic commands to control & monitor udev

• update hwdb configuration & apply updated rules & restart udev & trigger new rules:
  $ sudo udevadm hwdb --update && sudo udevadm control --reload-rules && sudo udevadm trigger

• monitor events in real time:
  $ udevadm monitor --udev [--environment]

• dump information about specific DEVICE:
  $ udevadm info -a -n /dev/DEVICE

Static names for devices using udev rules

• to set a static custom name for a device, create file inside /etc/udev/rules.d directory and add this line:
  SUBSYSTEM=="tty", ATTRS{bcdDevice}=="____", ATTRS{idProduct}=="____", ATTRS{idVendor}=="____", ATTRS{product}=="____", ATTRS{removable}=="removable", ATTRS{version}=="____", SYMLINK+="name"

• to ignore Modem Manager probing a device, add this line:
  ATTRS{idVendor}=="____", ATTRS{idProduct}=="____", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_TTY_BLACKLIST}="1", ENV{MTP_NO_PROBE}="1", ENV{ID_MM_PORT_IGNORE}="1", ENV{ID_MM_TTY_MANUAL_SCAN_ONLY}="1"

Execute script/app on attaching a specific device

• to run a command on [physical] attach of a device, add this line:
  ACTION=="add", ENV{DEVTYPE}=="usb_device", ATTR{idVendor}=="____", ATTR{idProduct}=="____", ENV{ID_MODEL}=="____", RUN+="/full/path/to/script/with/x/bits"

• content of script:

$ cat /full/path/to/script/with/x/bits
#!/usr/bin/env bash

# run command as root:
command

# run GUI app as a user:
su LOCAL_USER_NAME -c "DISPLAY=:0.0 /full/path/to/GUI/APP" &

# return to caller:
exit 0

Permission settings for devices

Group policies

• to get access to device which using tty subsystem without root/sudo, add your user to dialout group:
  $ sudo gpasswd -a ${USER} dialout
  or
  $ sudo usermod -a -G dialout ${USER}

• to get access to device which using usb subsystem without root/sudo, add your user to plugdev group:
  $ sudo gpasswd -a ${USER} plugdev
  or
  $ sudo usermod -a -G plugdev ${USER}

Generic permission udev rules for devices

• add this line to set permissions:
  SUBSYSTEM=="tty", ATTRS{bcdDevice}=="____", ATTRS{idProduct}=="____", ATTRS{idVendor}=="____", ATTRS{product}=="____", ATTRS{removable}=="removable", ATTRS{version}=="____", MODE="0664", GROUP="plugdev"