]>
Commit | Line | Data |
---|---|---|
eea1fd84 | 1 | udev - Linux userspace device management |
c2df8b5f | 2 | |
eea1fd84 KS |
3 | Integrating udev in the system has complex dependencies and may differ from |
4 | distribution to distribution. A system may not be able to boot up or work | |
5 | reliably without a properly installed udev version. The upstream udev project | |
a2ddee73 | 6 | does not recommend replacing a distro's udev installation with the upstream |
eea1fd84 KS |
7 | version. |
8 | ||
9 | The upstream udev project's set of default rules may require a most recent | |
67a77c8b | 10 | kernel release to work properly. This is currently version 2.6.32. |
c2df8b5f | 11 | |
0f50d0ef | 12 | Tools and rules shipped by udev are not public API and may change at any time. |
9698e70c | 13 | Never call any private tool in /lib/udev from any external application; it might |
0f50d0ef | 14 | just go away in the next release. Access to udev information is only offered |
600b2584 MW |
15 | by udevadm and libudev. Tools and rules in /lib/udev and the entire contents of |
16 | the /dev/.udev directory are private to udev and do change whenever needed. | |
c2df8b5f | 17 | |
c249f66a | 18 | Requirements: |
e3c14a7f | 19 | - Version 2.6.34 of the Linux kernel with sysfs, procfs, signalfd, inotify, |
67a77c8b KS |
20 | unix domain sockets, networking and hotplug enabled |
21 | ||
ab7863f7 KS |
22 | - Some architectures might need a later kernel, that supports accept4(), |
23 | or need to backport the accept4() syscall wiring in the kernel. | |
67a77c8b KS |
24 | |
25 | - These options are needed: | |
262d5cca KS |
26 | CONFIG_HOTPLUG=y |
27 | CONFIG_UEVENT_HELPER_PATH="" | |
28 | CONFIG_NET=y | |
29 | CONFIG_UNIX=y | |
30 | CONFIG_SYSFS=y | |
31 | CONFIG_SYSFS_DEPRECATED*=n | |
32 | CONFIG_PROC_FS=y | |
1da6c797 | 33 | CONFIG_INOTIFY_USER=y |
98ad80f8 | 34 | CONFIG_SIGNALFD=y |
67a77c8b KS |
35 | |
36 | - These options might be needed: | |
37 | CONFIG_TMPFS=y | |
e4c02c1c | 38 | CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes) |
a6c5b514 | 39 | CONFIG_BLK_DEV_BSG=y (SCSI devices) |
c2df8b5f | 40 | |
3fe44a29 | 41 | - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option. |
1e03b754 | 42 | |
a6c5b514 KS |
43 | - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work, |
44 | but it is not supported. | |
c2df8b5f | 45 | |
eea1fd84 KS |
46 | - The deprecated hotplug helper /sbin/hotplug should be disabled in the |
47 | kernel configuration, it is not needed today, and may render the system | |
48 | unusable because the kernel may create too many processes in parallel | |
49 | so that the system runs out-of-memory. | |
50 | ||
bde1af68 | 51 | - The proc filesystem must be mounted on /proc, and the sysfs filesystem must |
eea1fd84 KS |
52 | be mounted at /sys. No other locations are supported by a standard |
53 | udev installation. | |
c2df8b5f | 54 | |
67a77c8b | 55 | - The default rule sset requires the following group names resolvable at udev startup: |
bde1af68 | 56 | disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, and kmem. |
47d9121c MW |
57 | Especially in LDAP setups, it is required that getgrnam() be able to resolve |
58 | these group names with only the rootfs mounted and while no network is | |
67c89548 | 59 | available. |
c249f66a | 60 | |
d5d6a7f3 | 61 | - Some udev extras have external dependencies like: |
1224944f | 62 | libacl, libglib2, libusb, usbutils, pciutils, and gperf. |
d5d6a7f3 | 63 | All these extras can be disabled with configure options. |
c2df8b5f | 64 | |
eea1fd84 KS |
65 | Setup: |
66 | - At bootup, the /dev directory should get the 'devtmpfs' filesystem | |
3fe44a29 MW |
67 | mounted. Udev manages the permissions and ownership of the kernel-created |
68 | device nodes, and udev possibly creates additional symlinks. If needed, udev also | |
eea1fd84 KS |
69 | works on an empty 'tmpfs' filesystem, but some static device nodes like |
70 | /dev/null, /dev/console, /dev/kmsg are needed to be able to start udev itself. | |
c249f66a | 71 | |
eea1fd84 KS |
72 | - The udev daemon should be started to handle device events sent by the kernel. |
73 | During bootup, the kernel can be asked to send events for all already existing | |
e62c9c72 | 74 | devices so that they too can be configured by udev. This is usually done by: |
eea1fd84 KS |
75 | /sbin/udevadm trigger --type=subsystems |
76 | /sbin/udevadm trigger --type=devices | |
77 | ||
cb936a39 | 78 | - Restarting the daemon never applies any rules to existing devices. |
c2df8b5f | 79 | |
9698e70c | 80 | - New/changed rule files are picked up automatically; there is no daemon |
eea1fd84 KS |
81 | restart or signal needed. |
82 | ||
83 | Operation: | |
fd752623 MW |
84 | - Based on events the kernel sends out on device creation/removal, udev |
85 | creates/removes device nodes in the /dev directory. | |
eea1fd84 KS |
86 | |
87 | - All kernel events are matched against a set of specified rules, which | |
88 | possibly hook into the event processing and load required kernel | |
49500e9b | 89 | modules to set up devices. For all devices, the kernel exports a major/minor |
3fe44a29 | 90 | number; if needed, udev creates a device node with the default kernel |
eea1fd84 KS |
91 | name. If specified, udev applies permissions/ownership to the device |
92 | node, creates additional symlinks pointing to the node, and executes | |
93 | programs to handle the device. | |
94 | ||
95 | - The events udev handles, and the information udev merges into its device | |
96 | database, can be accessed with libudev: | |
97 | http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/ | |
98 | http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/ | |
99 | ||
d5d6a7f3 KS |
100 | For more details about udev and udev rules, see the udev man pages: |
101 | http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/ | |
c2df8b5f | 102 | |
a6c5b514 | 103 | Please direct any comment/question to the linux-hotplug mailing list at: |
98520be7 | 104 | linux-hotplug@vger.kernel.org |