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 2.6.25 of the Linux kernel with sysfs, procfs, signalfd, inotify, unix domain sockets, networking and hotplug enabled. - For reliable operation, the kernel must not use the CONFIG_SYSFS_DEPRECATED* option. - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not supported. - The proc filesystem must be mounted on /proc/, the sysfs filesystem must be mounted at /sys/. No other locations are supported by udev. - The system must have the following group names resolvable at udev startup: disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem. Especially in LDAP setups, it is required, that getgrnam() is able to resolve these group names with only the rootfs mounted, and while no network is available. Operation: Udev creates and removes device nodes in /dev/, based on events the kernel sends out on device discovery or removal. - Early in the boot process, the /dev/ directory should get a 'tmpfs' filesystem mounted, which is maintained 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 in the kernel configuration, it is not needed, and may render the system unusable because of a fork-bombing behavior. - 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