1. udev
  2. /dev


udev is responsible for dynamic device management needed for hot plugging devices. Information about configured and active devices is contained in the /dev virtual filesystem.

  • When a device changes state, the kernel sends an event to the systemd-udevd.service daemon.
    • The daemon searches configured rules to match the event
    • The udev rules are stored and read from the following locations: (check the udev manpage on your system)
      • /lib/udev/rules.d (system directory)
      • /run/udev/rules.d (volatile runtime directory)
      • /etc/udev/rules.d (local administration directory)
  • If you want to monitor udev events, use the command udevadm.


  • the /dev virtual filesystem describes the devices on your system.
  • The value in the first column represents the type of device it is:
    • b : block device (hdd)
    • c : character device (terminal, printer, special)
    • d : directory
    • l : symbolic link

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