UDev is the UserSpace-based replacement for DevFs, an obsolete LinuxKernel Module that creates entries for available devices in /dev. UDev is available in Kernel 2.5 and newer and uses HotPlug and the /sys FileSystem.
See also:
Q: Why doesn't the HAL and UDev combination pick up my device events (ie plugging in a KeyDrive) in DebianLinux?
A: You have to add the user to the "plugdev" group, else it won't work.
10 pages link to UDev:
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