kernel release to work properly. This is currently version 2.6.32.
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 contents of
-the /dev/.udev directory are private to udev and do change whenever needed.
+Never call any private tool in /usr/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 /usr/lib/udev and the entire contents
+of the /run/udev directory are private to udev and do change whenever needed.
Requirements:
- - Version 2.6.32 of the Linux kernel with sysfs, procfs, signalfd, inotify,
+ - Version 2.6.34 of the Linux kernel with sysfs, procfs, signalfd, inotify,
unix domain sockets, networking and hotplug enabled
- - ARM needs kernel version 2.6.36 or this patch:
- http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=21d93e2e29722d7832f61cc56d73fb
+ - Some architectures might need a later kernel, that supports accept4(),
+ or need to backport the accept4() syscall wiring in the kernel.
- These options are needed:
CONFIG_HOTPLUG=y
available.
- Some udev extras have external dependencies like:
- libacl, libglib2, libusb, usbutils, pciutils, and gperf.
+ libacl, libglib2, usbutils, pciutils, and gperf.
All these extras can be disabled with configure options.
Setup:
- At bootup, the /dev directory should get the 'devtmpfs' filesystem
mounted. Udev manages the permissions and ownership of the kernel-created
device nodes, and udev possibly creates additional symlinks. If needed, udev also
- 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.
+ works on an empty 'tmpfs' filesystem, but some device nodes like
+ /dev/null, /dev/console, /dev/kmsg should be created before udevd is started.
- 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 so that they too can be configured by udev. This is usually done by:
- /sbin/udevadm trigger --type=subsystems
- /sbin/udevadm trigger --type=devices
+ During bootup, the events for already existing devices can be replayed, so
+ that they are configured by udev. This is usually done by:
+ udevadm trigger --action=add --type=subsystems
+ udevadm trigger --action=add --type=devices
- Restarting the daemon never applies any rules to existing devices.
Operation:
- Based on events the kernel sends out on device creation/removal, udev
- creates/removes device nodes in the /dev directory.
+ 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
- name. If specified, udev applies permissions/ownership to the device
+ 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.