For more information see the files in the docs/ directory.
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.
+ Integrating udev in the system has complex dependencies and differs from distro
+ to distro. All major distros depend on udev these days and the system may not
+ work without a properly installed version. The upstream udev project does not
+ recommend to replace a distro's udev installation with the upstream version.
- 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.
+Requirements:
+ - Version 2.6.19 of the Linux kernel for reliable operation of this release of
+ udev. The kernel may have a requirement on udev too, see Documentation/Changes
+ in the kernel source tree for the actual dependency.
-udev requires:
- - 2.6 version of the Linux kernel
+ - The kernel must have sysfs, unix domain sockets and networking enabled.
+ (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
+ but it does not make any sense - don't complain if anything goes wrong.)
- - the kernel must have sysfs, netlink, and hotplug enabled
+ - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
+ be mounted at /sys/. No other locations are supported by udev.
- - proc must be mounted on /proc
- - sysfs must be mounted at /sys, no other location is supported
+Operation:
+ Udev creates and removes device nodes in /dev/, based on events the kernel
+ sends out on device discovery or removal.
- - udev creates and removes device nodes in /dev based on events
- the kernel sends out on device discovery or removal
+ - Very early in the boot process, the /dev/ directory 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.
- - 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)
+ - 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.
- - udev replaces the hotplug event management invoked from /sbin/hotplug
- by the udevd daemon, which receives the kernel events over netlink
+ - The old hotplug helper /sbin/hotplug should be disabled on bootup, 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 which
- make it posible to hook into the event processing
+ - The udevd daemon must be started on bootup to receive netlink uevents
+ from the kernel driver core.
- - 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)
+ - All kernel events are matched against a set of specified rules in
+ /lib/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 exports a major/minor number, udev will create a
+ device node with the default kernel name, or the one specified by a
+ matching udev rule.
-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
- DESTDIR
- prefix for install target 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.
- DEBUG
- if set to 'true', verbose debugging messages will be compiled into
- the udev binaries. Default value is 'false'.
- 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 in /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 program cdrom_id and scsi_id:
- make EXTRAS="extras/cdrom_id extras/scsi_id"
-
-Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
- linux-hotplug-devel@lists.sourceforge.net
+Please direct any comment/question/concern to the linux-hotplug mailing list at:
+ linux-hotplug@vger.kernel.org
~ianmdlvl / elogind.git / blobdiff