Important Note:
Integrating udev in the system is a whole lot of work, has complex dependencies
- and differs a lot from distro to distro. All reasonable distros use udev these
- days, the major ones make it mandatory and the system will not work without it.
+ and differs a lot from distro to distro. All reasonable distros depend on udev
+ these days and the system will not work without it.
The upstream udev project does not support or recomend to replace a distro's udev
installation with the upstream version. The installation of a unmodified upstream
version may render your system unusable! There is no "default" setup or a set
of "default" rules provided by the upstream udev version.
-udev requires:
- - 2.6 version of the Linux kernel
+Requirements:
+ - 2.6.x version of the Linux kernel. See the RELEASE-NOTES file in the
+ udev tree and the Documentation/Changes in the kernel source tree for
+ the actual dependency.
- - the kernel must have sysfs, netlink, and hotplug enabled
+ - The kernel must have sysfs and unix domain socket enabled.
+ (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
+ but it is completely silly, don't complain if anything goes wrong.)
- - proc must be mounted on /proc
+ - The proc filesystem must be mounted on /proc.
- - sysfs must be mounted at /sys, no other location is supported
+ - The sysfs filesystem must be mounted at /sys. No other location
+ will be supported by udev.
- - udev creates and removes device nodes in /dev based on events
- the kernel sends out on device discovery or removal
- - during bootup /dev usually gets a tmpfs mounted which is populated scratch
- by udev (created nodes don't survive a reboot, it always starts from scratch)
+Operation:
+ Udev creates and removes device nodes in /dev, based on events the kernel
+ sends out on device discovery or removal.
- - udev replaces the hotplug event management invoked from /sbin/hotplug
- by the udevd daemon, which receives the kernel events over netlink
+ - 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.
- - all kernel events are matched against a set of specified rules which
- make it posible to hook into the event processing
+ - 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.
- - there is a copy of the rules files for all major distros in the etc/udev
- directory (you may look there how others distros are doing it)
+ - The udevd daemon must be started by an init script to receive netlink
+ uevents from the kernel driver core.
-Setting which are used for building udev:
- prefix
- set this to the default root that you want to use
- Only override this if you really know what you are doing
+ - 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 for install target for package building
+ Prefix of install target, used for package building.
USE_LOG
- if set to 'true', udev will emit messages to the syslog when
- it creates or removes device nodes. This is helpful to see
- what udev is doing. This is enabled by default.
+ 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', verbose debugging messages will be compiled into
- the udev binaries. Default value is 'false'.
+ 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.
USE_SELINUX
- if set to 'true', udev will be built with SELinux support
+ 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.
+ If set to 'true', udev is built and linked against klibc.
Default value is 'false'. KLCC specifies the klibc compiler
- wrapper, usually in /usr/bin/klcc
+ 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 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).
-if you want to build the udev helper program cdrom_id and scsi_id:
- make EXTRAS="extras/cdrom_id extras/scsi_id"
+ - 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
~ianmdlvl / elogind.git / blobdiff