1 udev - userspace device management
3 Integrating udev in the system has complex dependencies and differs from distro
4 to distro. All major distros depend on udev these days and the system may not
5 work without a properly installed version. The upstream udev project does not
6 recommend to replace a distro's udev installation with the upstream version.
8 Tools and rules shipped by udev are not public API and may change at any time.
9 Never call any private tool in /lib/udev from any external application, it might
10 just go away in the next release. Access to udev information is only offered
11 by udevadm and libudev. Everything in /lib/udev and /dev/.udev/ is 100% private
15 - Version 2.6.25 of the Linux kernel with sysfs, procfs, signalfd, inotify,
16 unix domain sockets, networking and hotplug enabled:
18 CONFIG_UEVENT_HELPER_PATH=""
22 CONFIG_SYSFS_DEPRECATED*=n
25 CONFIG_TMPFS_POSIX_ACL=y
29 - For reliable operation, the kernel must not use the CONFIG_SYSFS_DEPRECATED*
32 - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
35 - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
36 be mounted at /sys/. No other locations are supported by udev.
38 - The system must have the following group names resolvable at udev startup:
39 disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
40 Especially in LDAP setups, it is required, that getgrnam() is able to resolve
41 these group names with only the rootfs mounted, and while no network is
44 - To build all udev extras, libacl, libglib2, libusb, usbutils, pciutils,
45 gperf are needed. These dependencies can be disabled with the
46 --disable-extras option.
49 Udev creates and removes device nodes in /dev/, based on events the kernel
50 sends out on device discovery or removal.
52 - Early in the boot process, the /dev/ directory should get a 'tmpfs'
53 filesystem mounted, which is maintained by udev. Created nodes or changed
54 permissions will not survive a reboot, which is intentional.
56 - The content of /lib/udev/devices/ directory which contains the nodes,
57 symlinks and directories, which are always expected to be in /dev, should
58 be copied over to the tmpfs mounted /dev, to provide the required nodes
59 to initialize udev and continue booting.
61 - The old hotplug helper /sbin/hotplug should be disabled in the kernel
62 configuration, it is not needed, and may render the system unusable
63 because of a fork-bombing behavior.
65 - All kernel events are matched against a set of specified rules in
66 /lib/udev/rules.d/ which make it possible to hook into the event
67 processing to load required kernel modules and setup devices. For all
68 devices the kernel exports a major/minor number, udev will create a
69 device node with the default kernel name, or the one specified by a
72 Please direct any comment/question/concern to the linux-hotplug mailing list at:
73 linux-hotplug@vger.kernel.org