+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 is a whole lot of work, has complex dependencies
+ and differs a lot from distro to distro. All major distros depend on udev these
+ days and the system may not work without a proper installed version. The upstream
+ udev project does not support or recommend to replace a distro's udev installation
+ with the upstream version. The installation of a unmodified upstream version may
+ render your system unusable. Until now, there is no "default" setup or a set of
+ "default" rules provided by the upstream udev version.
-To use:
+Requirements:
+ - 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.
-- Edit the udev.h file and replace the following variables with values
- that make sense for your system:
- #define SYSFS_ROOT "/sys"
- #define UDEV_ROOT "/home/greg/linux/udev/"
- #define DEV_FILE "/dev"
- #define MKNOD "/bin/mknod"
- The only value most people will have to change is the UDEV_ROOT
- variable, as I doubt you really want device nodes to be created in my
- home directory :)
+ - 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.)
-- Run make to build the project.
+ - The proc filesystem must be mounted on /proc, the sysfs filesystem must
+ be mounted at /sys. No other location will be supported by udev.
-- Make sure sysfs is mounted.
-- Point /proc/sys/kernel/hotplug at the location of the udev binary that
- is created. Then plug some block devices in, or other types of
- devices that create dev files in sysfs. An easy way to do this,
- without any hardware is to use the scsi_debug module to create virtual
- scsi devices.
+Operation:
+ Udev creates and removes device nodes in /dev, based on events the kernel
+ sends out on device discovery or removal.
-- Watch as the nodes get created and removed.
+ - 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.
+ - 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.
-Yes this is a really rough first cut, I know. It's mostly a proof of
-concept that this can actually work. See the TODO file for a list of
-things left to be done.
+ - 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.
-Any comment/questions/concerns please let me know.
+ - 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 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.
+
+
+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.
+ USE_SELINUX
+ If set to 'true', udev will be built with SELinux support
+ enabled. This is disabled by default.
+ EXTRAS
+ list of helper programs in extras/ to build.
+ 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 /lib/udev or /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 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
-greg k-h
-greg@kroah.com
~ianmdlvl / elogind.git / blobdiff