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. This is currently version 2.6.31.
+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
+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,
- unix domain sockets, networking and hotplug enabled:
+ - Version 2.6.32 of the Linux kernel with sysfs, procfs, signalfd, inotify,
+ unix domain sockets, networking and hotplug enabled
+
+ - 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
CONFIG_UEVENT_HELPER_PATH=""
CONFIG_NET=y
CONFIG_SYSFS=y
CONFIG_SYSFS_DEPRECATED*=n
CONFIG_PROC_FS=y
- CONFIG_TMPFS=y
CONFIG_INOTIFY_USER=y
CONFIG_SIGNALFD=y
+
+ - These options might be needed:
+ CONFIG_TMPFS=y
CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
CONFIG_BLK_DEV_BSG=y (SCSI devices)
- - Udev will not work with the CONFIG_SYSFS_DEPRECATED* option.
+ - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option.
- Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
but it is not supported.
unusable because the kernel may create too many processes in parallel
so that the system runs out-of-memory.
- - The proc filesystem must be mounted on /proc, the sysfs filesystem must
+ - 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 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
+ - 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.
- - To build all 'udev extras', libacl, libglib2, libusb, usbutils, pciutils,
- gperf are needed. These dependencies can be disabled with the
- --disable-extras configure option.
+ - Some udev extras have external dependencies like:
+ libacl, libglib2, libusb, 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 will manage permissions and ownership of the kernel-created
- device nodes, and possibly create additional symlinks. If needed, udev also
+ 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.
- - 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:
+ 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
- - Restarting the daemon does never apply any rules to existing devices.
+ - Restarting the daemon never applies 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:
- - Udev creates/removes device nodes in /dev, based on events the kernel
- sends out on device creation/removal.
+ - Based on events the kernel sends out on device creation/removal, udev
+ creates/removes device nodes 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 setup devices. For all devices the kernel exports a major/minor
- number, if needed, udev will create a device node with the default 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
node, creates additional symlinks pointing to the node, and executes
programs to handle the device.
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(7) man page.
+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
~ianmdlvl / elogind.git / blobdiff