Editing Udev (section)

==Overview==
Unlike traditional [[Unix]] systems, where the [[device node]]s in the {{mono|/dev}} directory have been a static set of files, the Linux udev device manager dynamically provides only the nodes for the devices actually present on a system. Although [[devfs]] used to provide similar functionality, [[Greg Kroah-Hartman]] cited a number of reasons<ref>{{cite web
 | url         = http://kernel.org/pub/linux/utils/kernel/hotplug/udev_vs_devfs
 | title       = udev and devfs - The final word
 | access-date  = 2008-01-24
 | format      = [[Plain text]]
 | author      = Greg Kroah-Hartman
 | author-link      = Greg Kroah-Hartman
 | archive-url  = https://web.archive.org/web/20110709174547/http://kernel.org/pub/linux/utils/kernel/hotplug/udev_vs_devfs
 | archive-date = 2011-07-09}}</ref> for preferring udev over devfs:
* udev supports persistent device naming, which does not depend on, for example, the order in which the devices are plugged into the system. The default udev setup provides persistent names for storage devices. Any hard disk is recognized by its unique filesystem id, the name of the disk and the physical location on the hardware it is connected to.
* udev executes entirely in [[user space]], as opposed to devfs's [[kernel space]]. One consequence is that udev moved the naming policy out of the kernel and can run arbitrary programs to compose a name for the device from the device's properties, before the node is created; there, the whole process is also interruptible and it runs with a lower priority.

The udev, as a whole, is divided into three parts:
* [[Library (computing)|Library]] ''libudev'' that allows access to device information; it was incorporated into the [[systemd]] 183 software bundle.<ref name=":0">{{Cite web|url=https://github.com/systemd/systemd/blob/v183/NEWS|title=systemd/systemd|website=GitHub|access-date=2016-08-21}}</ref>
* User space [[Daemon (computing)|daemon]] {{Mono|udevd}} that manages the virtual {{Mono|/dev}}.
* Administrative [[command-line utility]] {{Mono|udevadm}} for diagnostics.

The system gets calls from the kernel via [[netlink]] socket. Earlier versions used [[Hotplug (software)|hotplug]], adding a link to themselves in {{mono|/etc/hotplug.d/default}} with this purpose.