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faq_udev.md

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Rules for udev & permissions for devices HOWTO

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

Basic commands to control & monitor udev

  • apply rules & restart udev & trigger new rules:
    $ 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"