1 udev - userspace device management
3 For more information see the files in the docs/ directory.
6 Integrating udev in the system is a whole lot of work, has complex dependencies
7 and differs a lot from distro to distro. All major distros depend on udev these
8 days and the system may not work without a proper installed version. The upstream
9 udev project does not support or recomend to replace a distro's udev installation
10 with the upstream version. The installation of a unmodified upstream version may
11 render your system unusable. Until now, there is no "default" setup or a set of
12 "default" rules provided by the upstream udev version.
15 - 2.6.x version of the Linux kernel. See the RELEASE-NOTES file in the
16 udev tree and the Documentation/Changes in the kernel source tree for
17 the actual dependency.
19 - The kernel must have sysfs and unix domain socket enabled.
20 (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
21 but it is completely silly - don't complain if anything goes wrong.)
23 - The proc filesystem must be mounted on /proc.
25 - The sysfs filesystem must be mounted at /sys. No other location
26 will be supported by udev.
30 Udev creates and removes device nodes in /dev, based on events the kernel
31 sends out on device discovery or removal.
33 - Early in the boot process, the /dev directory should get a tmpfs
34 filesystem mounted, which is populated from scratch by udev. Created nodes
35 or changed permissions will not survive a reboot, which is intentional.
37 - The content of /lib/udev/devices directory which contains the nodes,
38 symlinks and directories, which are always expected to be in /dev, should
39 be copied over to the tmpfs mounted /dev, to provide the required nodes
40 to initialize udev and continue booting.
42 - The udevd daemon must be started by an init script to receive netlink
43 uevents from the kernel driver core.
45 - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should
46 be disabled with an init script before actions like loading kernel
47 modules are taken, which may cause a lot of events.
49 - All kernel events are matched against a set of specified rules in
50 /etc/udev/rules.d/ which make it possible to hook into the event
51 processing to load required kernel modules and setup devices. For all
52 devices the kernel exports a major/minor number, udev will create a
53 device node with the default kernel name or the one specified by a
59 Prefix of install target, used for package building.
61 If set to 'true', udev is able to pass errors or debug information
62 to syslog. This is very useful to see what udev is doing or not doing.
63 It is enabled by default, don't expect any useful answer, if you
64 need to hunt a bug, but you can't enable syslog.
66 If set to 'true', very verbose debugging messages will be compiled
67 into the udev binaries. The actual level of debugging is specified
68 in the udev config file.
70 If set to 'true', udev will be built with SELinux support
71 enabled. This is disabled by default.
73 If set to 'true', udev is built and linked against klibc.
74 Default value is 'false'. KLCC specifies the klibc compiler
75 wrapper, usually located at /usr/bin/klcc.
77 list of helper programs in extras/ to build.
78 make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
82 - The install target intalls the udev binaries in the default locations,
83 All at boot time reqired binaries will be installed in /lib/udev or /sbin.
85 - The default location for scripts and binaries that are called from
86 rules is /lib/udev. Other packages who install udev rules, should use
89 - It is recommended to use the /lib/udev/devices directory to place
90 device nodes and symlinks in, which are copied to /dev at every boot.
91 That way, nodes for broken subsystems or devices which can't be
92 detected automatically by the kernel, will always be available.
94 - Copies of the rules files for the major distros are provided as examples
95 in the etc/udev directory.
97 - The persistent device naming links in /dev/disk/ are required by other
98 software that depends on the data udev has collected from the devices
99 and should be installed by default with every udev installation.
101 Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
102 linux-hotplug-devel@lists.sourceforge.net