+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 2.6.22 of the Linux kernel for reliable operation of this release of
+ udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
-- 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 is not
+ supported.
-- Run make to build the project.
+ - 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 sysfs is mounted.
+ - The system must have the following group names resolvable at udev startup:
+ disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
+ Especially in LDAP setups, it is required, that getgrnam() is able to resolve
+ these group names with only the rootfs mounted, and while no network is
+ available.
-- 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
+ /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
-greg k-h
-greg@kroah.com
~ianmdlvl / elogind.git / blobdiff