Editing Udev (section)

==Design==
[[Device driver]]s are part of the Linux kernel, in which their primary functions include device discovery, detecting device state changes, and similar low-level hardware functions. After loading a device driver into memory from the kernel, detected events are sent out to the userspace daemon udevd. It is the device manager, {{Mono|udevd}}, that catches all of these events and then decides what shall happen next. For this, {{Mono|udevd}} has a very comprehensive set of configuration files, which can all be adjusted by the computer administrator, according to their needs.

* In case a new storage device is connected over USB, {{Mono|udevd}} is notified by the kernel and itself notifies the udisksd-daemon. That daemon could then mount the file systems.
* In case a new Ethernet cable is plugged into the Ethernet NIC, {{Mono|udevd}} is notified by the kernel and itself notifies the NetworkManager-daemon. The NetworkManager-daemon could start dhclient for that NIC, or configure according to some manual configuration.

The complexity of doing so forced application authors to re-implement hardware support logic. Some hardware devices also required privileged helper programs to prepare them for use. These often have to be invoked in ways that could be awkward to express with the Unix permissions model (for example, allowing users to join [[wireless network]]s only if they are logged into the video console). Application authors resorted to using [[setuid]] binaries or run service [[Daemon (computing)|daemons]] to provide their own access control and privilege separation, potentially introducing security holes each time.<ref name="pennington">{{citation|title = Making Hardware Just Work|date = 2003-07-10|first = Havoc|last = Pennington|url = http://ometer.com/hardware.html}}</ref>

[[HAL (software)|HAL]] was created to deal with these challenges, but is now deprecated in most Linux distributions, its functionality being replaced by udevd.