+udev - userspace device management
-udev - a userspace implementation of devfs
+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.
-For more information on the design, and structure of this project, see the
-files in the docs/ directory.
+Tools and rules shipped by udev are not public API and may change at any time.
+Never call any private tool in /lib/udev from any external application, it might
+just go away in the next release. Access to udev information is only offered
+by udevadm and libudev. Tools and rules in /lib/udev and the entire content of
+/dev/.udev/ is private to udev.
-To use:
+Requirements:
+ - Version 2.6.25 of the Linux kernel with sysfs, procfs, signalfd, inotify,
+ unix domain sockets, networking and hotplug enabled:
+ CONFIG_HOTPLUG=y
+ CONFIG_UEVENT_HELPER_PATH=""
+ CONFIG_NET=y
+ CONFIG_UNIX=y
+ CONFIG_SYSFS=y
+ CONFIG_SYSFS_DEPRECATED*=n
+ CONFIG_PROC_FS=y
+ CONFIG_TMPFS=y
+ CONFIG_INOTIFY=y
+ CONFIG_SIGNALFD=y
+ CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+ CONFIG_BLK_DEV_BSG=y (SCSI tape devices)
-- 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 :)
+ - For reliable operation, the kernel must not use the CONFIG_SYSFS_DEPRECATED*
+ option.
-- Run make to build the project.
+ - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
+ supported.
-- Make sure sysfs is mounted.
+ - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
+ be mounted at /sys/. No other locations are supported by udev.
-- 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.
+ - 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.
-- Watch as the nodes get created and removed.
+ - To build all udev extras, libacl, libglib2, libusb, usbutils, pciutils,
+ gperf are needed. These dependencies can be disabled with the
+ --disable-extras option.
+Operation:
+ Udev creates and removes device nodes in /dev/, based on events the kernel
+ sends out on device discovery or removal.
-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.
+ - Early in the boot process, the /dev/ directory should get a 'tmpfs'
+ filesystem mounted, which is maintained by udev. Created nodes or changed
+ permissions will not survive a reboot, which is intentional.
-Any comment/questions/concerns please let me know.
+ - 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.
+
+ - The old hotplug helper /sbin/hotplug should be disabled in the kernel
+ configuration, it is not needed, and may render the system unusable
+ because of a fork-bombing behavior.
+
+ - 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