+udev - userspace device management
-udev - a userspace implementation of devfs
+For more information see the files in the docs/ directory.
-For more information on the design, and structure of this project, see the
-files in the docs/ directory.
+Important Note:
+ 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.
-To use:
+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.
-- You must be running a 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.)
-- Make sure sysfs is mounted. udev will figure out where sysfs is mounted, but
- the traditional place for it is at /sys. You can mount it by hand by running:
- mount -t sysfs none /sys
+ - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
+ be mounted at /sys/. No other locations are supported by udev.
-- Make sure you have the latest version of the linux-hotplug scripts. They are
- available at linux-hotplug.sf.net or from your local kernel.org mirror at:
- kernel.org/pub/linux/utils/kernel/hotplug/
- They are required in order for udev to work properly.
- If for some reason you do not install the hotplug scripts, you must tell the
- kernel to point the hotplug binary at wherever you install udev at. This can
- be done by:
- echo "/sbin/udev" > /proc/sys/kernel/hotplug
+Operation:
+ Udev creates and removes device nodes in /dev/, based on events the kernel
+ sends out on device discovery or removal.
-- Build the project:
- make
+ - 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.
- Note:
- There are a number of different flags that you can use when building
- udev. They are as follows:
- prefix - set this to the default root that you want udev to be
- installed into. This works just like the 'configure --prefix'
- script does. Default value is ''. Only override this if you
- really know what you are doing.
- KLIBC - if set to 'true', udev is built and linked against the included
- version of klibc. Default value is 'false'.
- DEBUG - if set to 'true', debugging messages will be sent to the syslog
- as udev is run. Default value is 'false'.
- DBUS - if set to 'true', DBUS messages will be sent everytime udev
- creates or removes a device node. This requires that DBUS
- development headers and libraries be present on your system to
- build properly. Default value is 'false'.
+ - 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.
- So, if you want to build udev using klibc with debugging messages, you
- would do:
- make KLIBC=true DEBUG=true
+ - 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.
+ - The udevd daemon must be started on bootup to receive netlink uevents
+ from the kernel driver core.
-- Install the project:
- make install
-
- This will put the udev binary in /sbin, create the /udev and /etc/udev
- directories, and place the udev configuration files in /etc/udev. You
- will probably want to edit the namedev.* files to create custom naming
- rules. More info on how the config files are set up are contained in
- comments in the files, and is located in the documentation.
-
-- Add and remove devices from the system and marvel as nodes are created
- and removed in /udev/ based on the device types.
-
-- If you later get sick of it, uninstall it:
- make uninstall
-
-
-Things are still quite rough, and it's a bit beyond proof of concept
-code. Help is very much appreciated, see the TODO file for a list of
-things left to be done.
-
-If you want to build using klibc, use the Makefile.klibc file:
- - read the klibc/klibc/README file for how to set up the linux
- symlink properly.
- - make clean
- - make -f Makefile.klibc
-and marvel at the tiny binary you just created :)
-
-Any comment/questions/concerns please let me know.
-
-greg k-h
-greg@kroah.com
-
+ - 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.
+Please direct any comment/question/concern to the linux-hotplug mailing list at:
+ linux-hotplug@vger.kernel.org
~ianmdlvl / elogind.git / blobdiff