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 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.
+ 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.
Requirements:
- - 2.6 version of the Linux kernel.
-
- - The kernel must have sysfs, netlink, and hotplug enabled.
+ - Version 2.6.15 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.
- - The proc filesystem must be mounted on /proc.
+ - 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 is completely silly - don't complain if anything goes wrong.)
- - The sysfs filesystem must be mounted at /sys. No other location
- is supported.
+ - The proc filesystem must be mounted on /proc, the sysfs filesystem must
+ be mounted at /sys. No other location is supported by udev.
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.
- - Directly after mounting the root filesystem, the udevd daemon must be
- started by an init script.
+ - 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.
- - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should
- be disabled with an init script before kernel modules are loaded.
+ - 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.
- - During bootup, /dev usually gets a tmpfs filesystem mounted which is
- populated from scratch by udev (created nodes don't survive a reboot,
- the /lib/udev/devices directory should be used for "static nodes").
+ - 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.
- - Udev replaces the hotplug event management invoked from /sbin/hotplug
- by the udevd daemon, which receives the kernel events over netlink.
+ - The udevd daemon must be started on bootup to receive netlink uevents
+ from the kernel driver core.
- - All kernel events are matched against a set of specified rules which
- make it possible to hook into the event processing.
+ - 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 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.
- - 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).
Compile Options:
- prefix
- Set this to the default root that you want to use only override
- this if you really know what you are doing even then, you probably
- don't do the right thing.
DESTDIR
- Prefix for install target, used for package building.
+ 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.
+ 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).
+ list of helper programs in extras/ to build.
+ make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
-If you want to build the udev helper program cdrom_id and scsi_id:
- make EXTRAS="extras/cdrom_id extras/scsi_id"
Installation:
- - The install target intall the udev binaries in the default locations,
- all at boot time reqired binaries will be installed in /sbin.
+ - The install target intalls the udev binaries in the default locations,
+ All at boot time reqired binaries will be installed in /lib/udev or /sbin.
- The default location for scripts and binaries that are called from
- rules is /lib/udev.
+ 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.
+ detected automatically by the kernel, will always be available.
+
+ - Copies of the rules files for the major distros are provided as examples
+ in the etc/udev directory.
+
+ - The persistent device naming links in /dev/disk/ are required by other
+ software that depends on the data udev has collected from the devices
+ and should be installed by default with every udev installation.
Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
- linux-hotplug-devel@lists.sourceforge.net
+ linux-hotplug@vger.kernel.org
~ianmdlvl / elogind.git / blobdiff