Integrating udev in the system has complex dependencies and may differ from
distribution to distribution. A system may not be able to boot up or work
reliably without a properly installed udev version. The upstream udev project
-does not recommend to replace a distro's udev installation with the upstream
+does not recommend replacing a distro's udev installation with the upstream
version.
The upstream udev project's set of default rules may require a most recent
-kernel release to work properly.
+kernel release to work properly. This is currently version 2.6.31.
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
+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
-the /dev/.udev directory is private to udev and does change whenever needed.
+by udevadm and libudev. Tools and rules in /lib/udev and the entire contents of
+the /dev/.udev directory are private to udev and do change whenever needed.
Requirements:
- Version 2.6.27 of the Linux kernel with sysfs, procfs, signalfd, inotify,
works on an empty 'tmpfs' filesystem, but some static device nodes like
/dev/null, /dev/console, /dev/kmsg are needed to be able to start udev itself.
- - The content of /lib/udev/devices directory which contains static content like
- symlinks and directories, which are always expected to be in /dev, should
- be copied over to the mounted /dev directory:
- cp -axT --remove-destination /lib/udev/devices /dev
-
- The udev daemon should be started to handle device events sent by the kernel.
During bootup, the kernel can be asked to send events for all already existing
devices, to apply the configuration to these devices. This is usually done by:
- Restarting the daemon does never apply any rules to existing devices.
- - New/changed rule files are picked up automatically, there is no daemon
+ - New/changed rule files are picked up automatically; there is no daemon
restart or signal needed.
Operation:
- All kernel events are matched against a set of specified rules, which
possibly hook into the event processing and load required kernel
modules to setup devices. For all devices the kernel exports a major/minor
- number, if needed, udev will create a device node with the default kernel
+ number; if needed, udev will create a device node with the default kernel
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.