Skip to content

Udev Rules

Infrastructure Banner

Jetson Xavier NX

ubuntu 24.04

Why Udev Rules#

udev rules create stable, named symlinks for hardware devices regardless of which /dev/videoN or /dev/ttyUSBN number the kernel assigns at boot. This is essential in robotics setups where devices are frequently plugged and unplugged and enumeration order is not guaranteed.

When a device is connected, the kernel assigns it a node such as /dev/video2. On the next plug event, it may become /dev/video7. udev intercepts that event and, based on the device's hardware attributes, creates a stable symlink such as /dev/micipsa/realsense_depth0 pointing to whichever node was assigned.

This mechanism also applies to containerised environments. Docker resolves the symlink at container start time and creates a device node at the path specified inside the container. The container always sees the same path regardless of host enumeration order.

Serial devices plug order

Installation#

Important

Both installation methods are equivalent and produce the same result.

Script installer is the recommended approach

If you wish to add an udev rule for a new device, refer to Adding Udev Rules For New Devices.

Script Installer#

To automatically apply the provided udev rules, execute the installation script found in the infra/scripts/installers folder:

chmod +x install_udev_rules.sh
sudo ./install_udev_rules.sh

The script will:

  • Locate the udev rule files stored in infra/udev/
  • Install the available following rules into /etc/udev/rules.d/:
    • 99-micipsa-cameras.rules
    • 99-micipsa-serial.rules
  • Reload the udev daemon so the new rules are active
  • Trigger udev to apply the rules to already-connected devices
  • Display the installed rule paths for confirmation

If the devices were already connected at the time of installation, you may need to unplug and reconnect them, or restart the system for the rules to take full effect.

Serial devices plug order

Manual Install#

Note

udev only loads rules placed under /etc/udev/rules.d/.

sudo cp 99-micipsa-serial.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules && sudo udevadm trigger

sudo cp 99-micipsa-cameras.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules && sudo udevadm trigger

Uninstall#

Script Uninstaller#

Note

The uninstaller script reverts all changes made by the installer.

Using the uninstaller script is the recommended removal method.

chmod +x uninstall_udev_rules.sh
sudo ./uninstall_udev_rules.sh

systemd script install

Manual Uninstall#

sudo rm -f /etc/udev/rules.d/99-micipsa-cameras.rules
sudo rm -f /etc/udev/rules.d/99-micipsa-serial.rules

sudo udevadm control --reload-rules
sudo udevadm trigger

Reconnect the USB devices or reboot the system to apply the changes.

Adding Udev Rules For New Devices#

To add new serial device udev rules, refer to Serial Udev Rules.

To add new camera device udev rules, refer to Camera Udev Rules.

Additional Information#

Rule Field Reference#

All udev rules share a common set of fields. The table below defines each field once, device-specific behaviour is noted in the relevant section.

Field Description
SUBSYSTEM Device subsystem to match, "video4linux" for cameras, "tty" for serial devices
ATTRS{idVendor} USB vendor ID (4-digit hex), inherited from a parent device in the USB tree
ATTRS{idProduct} USB product ID (4-digit hex), inherited from a parent device in the USB tree
ATTRS{serial} Hardware serial number, inherited from a parent device; omit if the device has none
ATTR{index} Node index within the device, stable across plugs; camera-specific
ENV{ID_USB_INTERFACE_NUM} USB interface number, differentiates stream groups on multi-interface devices; camera-specific
ENV{ID_PATH} Physical USB port path, use when idVendor and idProduct alone are ambiguous (no serial number, or duplicate hardware)
SYMLINK+="micipsa/..." Creates a stable symlink under /dev/micipsa/
MODE="0666" Device file permissions
GROUP Unix group granted access to the device, "video" for cameras, "dialout" for serial devices

Note

The plugdev group is specific to Intel RealSense cameras. For most other USB camera devices, the appropriate group is video.