If you’ve used Linux for very long, chances are you’ve seen changes to the way Linux handles device files. In Linux’s early days, device files were just ordinary files with appropriate attributes set, created by the mknod command in the /dev directory (or conceivably elsewhere). Then along came devfs, a kernel-based dynamic device filesystem that appeared in the 2.3.46 kernel. Adopted by some distributions, such as Mandrake and Gentoo, devfs created device files dynamically; however, devfs had some serious limitations and was removed from the kernel as of version 2.6.13. Its replacement is udev, a user-space program.
Linux distributions are adopting udev in a big way because it solves several problems in Linux device access, particularly for sites with extreme needs (such as the need to control thousands of hard disks) and for hot-pluggable devices (such as USB cameras and MP3 players). To gain control of your hardware on a system that uses udev, you should know how to manage it.
Chances are you won’t need to modify the standard udev configuration for hard disks, console devices, and so on, but you may need to tweak the udev configuration to use new or exotic hardware. Without such tweaks, Linux might not create device files for your hardware, or Linux might create device files with inappropriate names, ownership, or permissions. You might also want to modify ownership or permissions on RS-232 serial ports, audio device files, and so on.
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