1udev - userspace device management 2 3For more information see the files in the docs/ directory. 4 5Important Note: 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 recommend 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. 13 14Requirements: 15 - Version 2.6.15 of the Linux kernel for reliable operation of this release of 16 udev. The kernel may have a requirement on udev too, see Documentation/Changes 17 in the kernel source tree for the actual dependency. 18 19 - The kernel must have sysfs, unix domain sockets and networking 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.) 22 23 - The proc filesystem must be mounted on /proc, the sysfs filesystem must 24 be mounted at /sys. No other location will be supported by udev. 25 26 27Operation: 28 Udev creates and removes device nodes in /dev, based on events the kernel 29 sends out on device discovery or removal. 30 31 - Very early in the boot process, the /dev directory should get a 'tmpfs' 32 filesystem mounted, which is populated from scratch by udev. Created nodes 33 or changed permissions will not survive a reboot, which is intentional. 34 35 - The content of /lib/udev/devices directory which contains the nodes, 36 symlinks and directories, which are always expected to be in /dev, should 37 be copied over to the tmpfs mounted /dev, to provide the required nodes 38 to initialize udev and continue booting. 39 40 - The old hotplug helper /sbin/hotplug should be disabled on bootup, before 41 actions like loading kernel modules are taken, which may cause a lot of 42 events. 43 44 - The udevd daemon must be started on bootup to receive netlink uevents 45 from the kernel driver core. 46 47 - All kernel events are matched against a set of specified rules in 48 /etc/udev/rules.d/ which make it possible to hook into the event 49 processing to load required kernel modules and setup devices. For all 50 devices the kernel exports a major/minor number, udev will create a 51 device node with the default kernel name or the one specified by a 52 matching udev rule. 53 54 55Compile Options: 56 DESTDIR 57 Prefix of install target, used for package building. 58 USE_LOG 59 If set to 'true', udev is able to pass errors or debug information 60 to syslog. This is very useful to see what udev is doing or not doing. 61 It is enabled by default, don't expect any useful answer, if you 62 need to hunt a bug, but you can't enable syslog. 63 DEBUG 64 If set to 'true', very verbose debugging messages will be compiled 65 into the udev binaries. The actual level of debugging is specified 66 in the udev config file. 67 USE_SELINUX 68 If set to 'true', udev will be built with SELinux support 69 enabled. This is disabled by default. 70 EXTRAS 71 list of helper programs in extras/ to build. 72 make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id" 73 74 75Installation: 76 - The install target intalls the udev binaries in the default locations, 77 All at boot time reqired binaries will be installed in /lib/udev or /sbin. 78 79 - The default location for scripts and binaries that are called from 80 rules is /lib/udev. Other packages who install udev rules, should use 81 that directory too. 82 83 - It is recommended to use the /lib/udev/devices directory to place 84 device nodes and symlinks in, which are copied to /dev at every boot. 85 That way, nodes for broken subsystems or devices which can't be 86 detected automatically by the kernel, will always be available. 87 88 - Copies of the rules files for the major distros are provided as examples 89 in the etc/udev directory. 90 91 - The persistent device naming links in /dev/disk/ are required by other 92 software that depends on the data udev has collected from the devices 93 and should be installed by default with every udev installation. 94 95Please direct any comment/question/concern to the linux-hotplug-devel mailing list at: 96 linux-hotplug-devel@lists.sourceforge.net 97 98