- Udev creates and removes device nodes in /dev, based on events the kernel
- sends out on device discovery or removal.
-
- - Early in the boot process, /dev should get a tmpfs filesystem
- mounted, which is populated from scratch by udev. Created nodes or
- changed permissions will not survive a reboot, which is intentional.
-
- - The content of /lib/udev/devices directory which contains the nodes,
- symlinks and directories, which are always expected to be in /dev, should
- be copied over to the tmpfs mounted /dev, to provide the required nodes
- to initialize udev and continue booting.
-
- - The udevd daemon must be started by an init script to receive netlink
- uevents from the kernel driver core.
-
- - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should
- be disabled with an init script before actions like loading kernel
- modules are taken, which may cause a lot of events.
-
- - All kernel events are matched against a set of specified rules in
- /etc/udev/rules.d/ which make it possible to hook into the event
- processing to load required kernel modules and setup devices. For all
- devices the kernel requests a device node, udev will create one with
- the default name or the one specified by a matching udev rules.
-
-
-Compile Options:
- DESTDIR
- Prefix of install target, used for package building.
- USE_LOG
- If set to 'true', udev is able to pass errors or debug information
- to syslog. This is very useful to see what udev is doing or not doing.
- It is enabled by default, don't expect any useful answer, if you
- need to hunt a bug, but you can't enable syslog.
- DEBUG
- If set to 'true', very verbose debugging messages will be compiled
- into the udev binaries. The actual level of debugging is specified
- in the udev config file.
- STRIPCMD
- If udev is compiled for packaging an empty string can be passed
- to disable the stripping of the binaries.
- USE_SELINUX
- If set to 'true', udev will be built with SELinux support
- enabled. This is disabled by default.
- USE_KLIBC
- If set to 'true', udev is built and linked against klibc.
- Default value is 'false'. KLCC specifies the klibc compiler
- wrapper, usually located at /usr/bin/klcc.
- EXTRAS
- If set, will build the "extra" helper programs as specified
- as listed (see below for an example).
-
-If you want to build the udev helper programs:
- make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
-
-
-Installation:
- - The install target intalls the udev binaries in the default locations,
- All at boot time reqired binaries will be installed in /sbin.
-
- - The default location for scripts and binaries that are called from
- rules is /lib/udev. Other packages who install udev rules, should use
- that directory too.
-
- - It is recommended to use the /lib/udev/devices directory to place
- device nodes and symlinks in, which are copied to /dev at every boot.
- That way, nodes for broken subsystems or devices which can't be
- detected automatically by the kernel, will always be available.
-
- - Copies of the rules files for all major distros are in the etc/udev
- directory (you may look there how others distros are doing it).
-
- - The persistent disk links in /dev/disk are the de facto standard
- on Linux and should be installed with every default udev installation.
- The devfs naming scheme rules are not recommended and not supported.
-
-Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
- linux-hotplug-devel@lists.sourceforge.net
-
+ - Based on events the kernel sends out on device creation/removal, udev
+ creates/removes device nodes in the /dev directory.
+
+ - All kernel events are matched against a set of specified rules, which
+ possibly hook into the event processing and load required kernel
+ modules to set up devices. For all devices, the kernel exports a major/minor
+ number; if needed, udev creates a device node with the default kernel
+ name. If specified, udev applies permissions/ownership to the device
+ node, creates additional symlinks pointing to the node, and executes
+ programs to handle the device.
+
+ - The events udev handles, and the information udev merges into its device
+ database, can be accessed with libudev:
+ http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/
+ http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/
+
+For more details about udev and udev rules, see the udev man pages:
+ http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/
+
+Please direct any comment/question to the linux-hotplug mailing list at:
+ linux-hotplug@vger.kernel.org