udev - userspace device management For more information see the files in the docs/ directory. Important Note: Integrating udev in the system has complex dependencies and differs from distro to distro. All major distros depend on udev these days and the system may not work without a properly installed version. The upstream udev project does not recommend to replace a distro's udev installation with the upstream version. Requirements: - Version 2.6.19 of the Linux kernel for reliable operation of this release of udev. The kernel may have a requirement on udev too, see Documentation/Changes in the kernel source tree for the actual dependency. - The kernel must have sysfs, unix domain sockets and networking enabled. (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work, but it does not make any sense - don't complain if anything goes wrong.) - The proc filesystem must be mounted on /proc/, the sysfs filesystem must be mounted at /sys/. No other locations are supported by udev. Operation: Udev creates and removes device nodes in /dev/, based on events the kernel sends out on device discovery or removal. - Very early in the boot process, the /dev/ directory should get a 'tmpfs' filesystem mounted, which is populated from scratch by udev. Created nodes or changed permissions will not survive a reboot, which is intentional. - The content of /lib/udev/devices/ directory which contains the nodes, symlinks and directories, which are always expected to be in /dev, should be copied over to the tmpfs mounted /dev, to provide the required nodes to initialize udev and continue booting. - The old hotplug helper /sbin/hotplug should be disabled on bootup, before actions like loading kernel modules are taken, which may cause a lot of events. - The udevd daemon must be started on bootup to receive netlink uevents from the kernel driver core. - All kernel events are matched against a set of specified rules in /lib/udev/rules.d/ which make it possible to hook into the event processing to load required kernel modules and setup devices. For all devices the kernel exports a major/minor number, udev will create a device node with the default kernel name, or the one specified by a matching udev rule. Please direct any comment/question/concern to the linux-hotplug mailing list at: linux-hotplug@vger.kernel.org