1 udev - userspace device management
3 For more information see the files in the docs/ directory.
6 Integrating udev in the system has complex dependencies and differs from distro
7 to distro. All major distros depend on udev these days and the system may not
8 work without a properly installed version. The upstream udev project does not
9 recommend to replace a distro's udev installation with the upstream version.
12 - Version 2.6.22 of the Linux kernel for reliable operation of this release of
13 udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
15 - The kernel must have sysfs, unix domain sockets and networking enabled.
16 Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
19 - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
20 be mounted at /sys/. No other locations are supported by udev.
22 - The system must have the following group names resolvable at udev startup:
23 disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
24 Especially in LDAP setups, it is required, that getgrnam() is able to resolve
25 these group names with only the rootfs mounted, and while no network is
29 Udev creates and removes device nodes in /dev/, based on events the kernel
30 sends out on device discovery or removal.
32 - Very early in the boot process, the /dev/ directory should get a 'tmpfs'
33 filesystem mounted, which is populated from scratch by udev. Created nodes
34 or changed permissions will not survive a reboot, which is intentional.
36 - The content of /lib/udev/devices/ directory which contains the nodes,
37 symlinks and directories, which are always expected to be in /dev, should
38 be copied over to the tmpfs mounted /dev, to provide the required nodes
39 to initialize udev and continue booting.
41 - The old hotplug helper /sbin/hotplug should be disabled on bootup, before
42 actions like loading kernel modules are taken, which may cause a lot of
45 - The udevd daemon must be started on bootup to receive netlink uevents
46 from the kernel driver core.
48 - All kernel events are matched against a set of specified rules in
49 /lib/udev/rules.d/ which make it possible to hook into the event
50 processing to load required kernel modules and setup devices. For all
51 devices the kernel exports a major/minor number, udev will create a
52 device node with the default kernel name, or the one specified by a
55 Please direct any comment/question/concern to the linux-hotplug mailing list at:
56 linux-hotplug@vger.kernel.org