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.
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,
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.
+ disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, and 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
available.
- To build all 'udev extras', libacl, libglib2, libusb, usbutils, pciutils,
- gperf are needed. These dependencies can be disabled with the
+ and gperf are needed. These dependencies can be disabled with the
--disable-extras configure option.
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.
- 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 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.
~ianmdlvl / elogind.git / blobdiff