version.
The upstream udev project's set of default rules may require a most recent
-kernel release to work properly. This is currently version 2.6.32.
+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 2.6.32 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
- 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:
+ - 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_INOTIFY_USER=y
CONFIG_SIGNALFD=y
+ CONFIG_SYSFS=y
+ CONFIG_SYSFS_DEPRECATED*=n
+ CONFIG_UEVENT_HELPER_PATH=""
- 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)
+ 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
available.
- Some udev extras have external dependencies like:
- libacl, libglib2, libusb, usbutils, pciutils, and gperf.
+ 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 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. 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 no daemon
- restart or signal needed.
+ - 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 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.
~ianmdlvl / elogind.git / blobdiff