udev
also: userspace /dev, device manager
A dynamic device manager for Linux that automatically detects hardware and creates device files in /dev, replacing the older static devfs system.
udev (userspace /dev) handles the creation and removal of device nodes when hardware is plugged in or detected by the kernel. When the kernel discovers a device, udev receives an event and uses a set of rules to determine what device file to create, what permissions to assign, and what symlinks to generate.
Device files (like /dev/sda for hard drives or /dev/ttyUSB0 for USB serial devices) are created dynamically as devices appear, rather than being pre-created statically. This is especially useful for removable media and hot-pluggable devices.
Configuration rules are stored in /etc/udev/rules.d/ and /usr/lib/udev/rules.d/, allowing administrators to customize how devices are named and what happens when they're detected. For example, you might write a rule to automatically mount a USB drive or grant specific permissions to a camera device.