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 2.6.25 of the Linux kernel with sysfs, procfs, signalfd, inotify,
13 unix domain sockets, networking and hotplug enabled:
15 CONFIG_UEVENT_HELPER_PATH=""
19 CONFIG_SYSFS_DEPRECATED*=n
22 CONFIG_TMPFS_POSIX_ACL=y
26 - For reliable operation, the kernel must not use the CONFIG_SYSFS_DEPRECATED*
29 - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
32 - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
33 be mounted at /sys/. No other locations are supported by udev.
35 - The system must have the following group names resolvable at udev startup:
36 disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
37 Especially in LDAP setups, it is required, that getgrnam() is able to resolve
38 these group names with only the rootfs mounted, and while no network is
41 - To build all udev extras, libacl, libglib2, libusb, usbutils, pciutils are
42 needed. These dependencies can be disabled with the --disable-extras option.
45 Udev creates and removes device nodes in /dev/, based on events the kernel
46 sends out on device discovery or removal.
48 - Early in the boot process, the /dev/ directory should get a 'tmpfs'
49 filesystem mounted, which is maintained by udev. Created nodes or changed
50 permissions will not survive a reboot, which is intentional.
52 - The content of /lib/udev/devices/ directory which contains the nodes,
53 symlinks and directories, which are always expected to be in /dev, should
54 be copied over to the tmpfs mounted /dev, to provide the required nodes
55 to initialize udev and continue booting.
57 - The old hotplug helper /sbin/hotplug should be disabled in the kernel
58 configuration, it is not needed, and may render the system unusable
59 because of a fork-bombing behavior.
61 - All kernel events are matched against a set of specified rules in
62 /lib/udev/rules.d/ which make it possible to hook into the event
63 processing to load required kernel modules and setup devices. For all
64 devices the kernel exports a major/minor number, udev will create a
65 device node with the default kernel name, or the one specified by a
68 Please direct any comment/question/concern to the linux-hotplug mailing list at:
69 linux-hotplug@vger.kernel.org