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 reasonable distros depend on udev
8 these days and the system will not work without it.
10 The upstream udev project does not support or recomend to replace a distro's udev
11 installation with the upstream version. The installation of a unmodified upstream
12 version may render your system unusable! There is no "default" setup or a set
13 of "default" rules provided by the upstream udev version.
16 - 2.6.x version of the Linux kernel. See the RELEASE-NOTES file in the
17 udev tree and the Documentation/Changes in the kernel source tree for
18 the actual dependency.
20 - The kernel must have sysfs and unix domain socket enabled.
21 (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
22 but it is completely silly, don't complain if anything goes wrong.)
24 - The proc filesystem must be mounted on /proc.
26 - The sysfs filesystem must be mounted at /sys. No other location
27 will be supported by udev.
31 Udev creates and removes device nodes in /dev, based on events the kernel
32 sends out on device discovery or removal.
34 - Directly after mouting the real root filesystem, wherever that
35 happens, in initramfs or with a directly mounted root, /dev should get
36 a tmpfs filesystem mounted, which is populated from scratch by udev.
37 Created nodes or changed permissions don't survive a reboot.
39 - The content of /lib/udev/devices directory which contains the nodes,
40 symlinks and directories, which are always expected to be in/dev, should
41 be copied over to the tmpfs mounted /dev, to provide the required nodes
42 to initialize udev and continue booting.
44 - The udevd daemon must be started by an init script to receive netlink
45 events from the kernel driver core.
47 - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should
48 be disabled with an init script before the boot scripts are run and
49 kernel modules are loaded.
51 - All kernel events are matched against a set of specified rules in
52 /etc/udev/rules.d/ which make it possible to hook into the event
53 processing to load required kernel modules and setup devices. For all
54 devices the kernel requests a device node, udev will create one with
55 the default name or the one specified by a matching udev rules.
60 Set this to the default root that you want to use. Only override
61 this if you really know what you are doing, even then, you probably
62 don't do the right thing.
64 Prefix for install target, used for package building.
66 If set to 'true', udev is able to pass errors or debug information
67 to syslog. This is very useful to see what udev is doing or not doing.
68 It is enabled by default, don't expect any useful answer, if you
69 need to hunt a bug, but you can't enable syslog.
71 If set to 'true', very verbose debugging messages will be compiled
72 into the udev binaries. The actual level of debugging is specified
73 in the udev config file.
75 If udev is compiled for packaging an empty string can be passed
76 to disable the stripping of the binaries.
78 If set to 'true', udev will be built with SELinux support
79 enabled. This is disabled by default.
81 If set to 'true', udev is built and linked against klibc.
82 Default value is 'false'. KLCC specifies the klibc compiler
83 wrapper, usually located at /usr/bin/klcc.
85 If set, will build the "extra" helper programs as specified
86 as listed (see below for an example).
88 If you want to build the udev helper programs:
89 make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
93 - The install target intalls the udev binaries in the default locations,
94 All at boot time reqired binaries will be installed in /sbin.
96 - The default location for scripts and binaries that are called from
97 rules is /lib/udev. Other packages who install udev rules, should use
100 - It is recommended to use the /lib/udev/devices directory to place
101 device nodes and symlinks in, which are copied to /dev at every boot.
102 That way, nodes for broken subsystems or devices which can't be
103 detected automatically by the kernel, will always be available.
105 - Copies of the rules files for all major distros are in the etc/udev
106 directory (you may look there how others distros are doing it).
108 - The persistent disk links in /dev/disk are the de facto standard
109 on Linux and should be installed with every default udev installation.
110 The devfs naming scheme rules are not recommended and not supported.
112 Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
113 linux-hotplug-devel@lists.sourceforge.net