+ - The proc filesystem must be mounted on /proc, and the sysfs filesystem must
+ be mounted at /sys. No other locations are supported by a standard
+ udev installation.
+
+ - The default rule sset requires the following group names resolvable at udev startup:
+ disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, and kmem.
+ Especially in LDAP setups, it is required that getgrnam() be able to resolve
+ these group names with only the rootfs mounted and while no network is
+ available.
+
+ - Some udev extras have external dependencies like:
+ libglib2, usbutils, pciutils, and gperf.
+ All these extras can be disabled with configure options.
+
+Setup:
+ - The udev daemon should be started to handle device events sent by the kernel.
+ During bootup, the events for already existing devices can be replayed, so
+ that they are configured by udev. The systemd service files contain the
+ needed commands to start the udev daemon and the coldplug sequence.
+
+ - Restarting the daemon never applies any rules to existing devices.
+
+ - New/changed rule files are picked up automatically; there is usually no
+ daemon restart or signal needed.
+
+Operation:
+ - Based on events the kernel sends out on device creation/removal, udev
+ creates/removes device nodes and symlinks in the /dev directory.
+
+ - All kernel events are matched against a set of specified rules, which
+ possibly hook into the event processing and load required kernel
+ modules to set up devices. For all devices, the kernel exports a major/minor
+ number; if needed, udev creates a device node with the default kernel
+ device name. If specified, udev applies permissions/ownership to the device
+ node, creates additional symlinks pointing to the node, and executes
+ programs to handle the device.
+
+ - The events udev handles, and the information udev merges into its device
+ database, can be accessed with libudev:
+ http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/
+ http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/
+
+For more details about udev and udev rules, see the udev man pages:
+ http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/
+
+Please direct any comment/question to the linux-hotplug mailing list at:
+ linux-hotplug@vger.kernel.org