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.
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 2.6.27 of the Linux kernel with sysfs, procfs, signalfd, inotify,
- unix domain sockets, networking and hotplug enabled:
+ - Version 2.6.34 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 required:
+ CONFIG_DEVTMPFS=y
CONFIG_HOTPLUG=y
- CONFIG_UEVENT_HELPER_PATH=""
+ CONFIG_INOTIFY_USER=y
CONFIG_NET=y
- CONFIG_UNIX=y
- CONFIG_SYSFS=y
- CONFIG_SYSFS_DEPRECATED*=n
CONFIG_PROC_FS=y
- CONFIG_TMPFS=y
- CONFIG_INOTIFY_USER=y
CONFIG_SIGNALFD=y
- CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+ CONFIG_SYSFS=y
+ CONFIG_SYSFS_DEPRECATED*=n
+ CONFIG_UEVENT_HELPER_PATH=""
+
+ - These options might be needed:
CONFIG_BLK_DEV_BSG=y (SCSI devices)
+ CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+
+ - The /dev directory needs the 'devtmpfs' filesystem mounted.
+ Udev only manages the permissions and ownership of the
+ kernel-provided device nodes, and possibly creates additional symlinks.
- - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option.
+ - Udev requires /run to be writable, which is usually done by mounting a
+ 'tmpfs' filesystem.
- - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
- but it is not supported.
+ - This version of udev does not work properly with the CONFIG_SYSFS_DEPRECATED*
+ option enabled.
- The deprecated hotplug helper /sbin/hotplug should be disabled in the
kernel configuration, it is not needed today, and may render the system
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:
+ 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.
-
- 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:
- /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. The systemd service files contain the
+ needed commands to start the udev daemon and the coldplug sequence.
- - 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
- restart or signal needed.
+ - New/changed rule files are picked up automatically; there is usually 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 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 setup devices. For all devices the kernel exports a major/minor
+ 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.
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