Udev creates and removes device nodes in /dev, based on events the kernel sends out on device discovery or removal. In other words, Udev is the system that maps hardware devices to files you can interact with in the /dev directory. Udev runs in user space and creates points in /dev when the kernel detects and recognizes new hardware as it’s attached. It’s only been around since 2003/2004. All modern distributions use udev instead of the now depreciated hotplug.