How does udev work with a USB mouse?
Instead of manually searching for connected devices, udev requests all device events from the kernel after the root file system is available, so the event for the USB mouse device runs again. Now it finds the kernel module on the mounted root file system and the USB mouse can be initialized.
Why does udev request device events from kernel?
The event for the device discovery was lost and failed to find a kernel module for the device. Instead of manually searching for connected devices, udev requests all device events from the kernel after the root file system is available, so the event for the USB mouse device runs again.
What happens to the / dev directory in udev?
With udev, the /dev directory reflects the current state of the kernel. Every kernel device has one corresponding device file. If a device is disconnected from the system, the device node is removed. The content of the /dev directory is kept on a temporary file system and all files are rendered at every system start-up.
Where are the device nodes located in udev?
The device nodes in the /dev directory provide access to the corresponding kernel devices. With udev, the /dev directory reflects the current state of the kernel. Every kernel device has one corresponding device file. If a device is disconnected from the system, the device node is removed.
How to use udev for device detection and management in Linux?
ENV {DEVTYPE}: matches against a device property value, device type in this case. RUN: specifies a program or script to execute as part of the event handling. Save the file and close it. Then as root, tell systemd-udevd to reload the rules files (this also reloads other databases such as the kernel module index), by running.
What does the udev line in uevent mean?
The UDEV lines show the finished udev event handlers. The timing is printed in microseconds. The time between UEVENT and UDEV is the time udev took to process this event or the udev daemon has delayed its execution to synchronize this event with related and already running events.