mirror of
https://github.com/systemd/systemd.git
synced 2024-12-26 03:22:00 +03:00
58 lines
2.6 KiB
Plaintext
58 lines
2.6 KiB
Plaintext
udev - userspace device management
|
|
|
|
For more information see the files in the docs/ directory.
|
|
|
|
Important Note:
|
|
Integrating udev in the system has complex dependencies and differs from distro
|
|
to distro. All major distros depend on udev these days and the system may not
|
|
work without a properly installed version. The upstream udev project does not
|
|
recommend to replace a distro's udev installation with the upstream version.
|
|
|
|
Requirements:
|
|
- Version 2.6.22 of the Linux kernel for reliable operation of this release of
|
|
udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
|
|
|
|
- The kernel must have sysfs, unix domain sockets and networking enabled.
|
|
Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
|
|
supported.
|
|
|
|
- The proc filesystem must be mounted on /proc/, the sysfs filesystem must
|
|
be mounted at /sys/. No other locations are supported by udev.
|
|
|
|
- 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
|
|
available.
|
|
|
|
Operation:
|
|
Udev creates and removes device nodes in /dev/, based on events the kernel
|
|
sends out on device discovery or removal.
|
|
|
|
- Very early in the boot process, the /dev/ directory should get a 'tmpfs'
|
|
filesystem mounted, which is populated from scratch by udev. Created nodes
|
|
or changed permissions will not survive a reboot, which is intentional.
|
|
|
|
- The content of /lib/udev/devices/ directory which contains the nodes,
|
|
symlinks and directories, which are always expected to be in /dev, should
|
|
be copied over to the tmpfs mounted /dev, to provide the required nodes
|
|
to initialize udev and continue booting.
|
|
|
|
- The old hotplug helper /sbin/hotplug should be disabled on bootup, before
|
|
actions like loading kernel modules are taken, which may cause a lot of
|
|
events.
|
|
|
|
- The udevd daemon must be started on bootup to receive netlink uevents
|
|
from the kernel driver core.
|
|
|
|
- All kernel events are matched against a set of specified rules in
|
|
/lib/udev/rules.d/ which make it possible to hook into the event
|
|
processing to load required kernel modules and setup devices. For all
|
|
devices the kernel exports a major/minor number, udev will create a
|
|
device node with the default kernel name, or the one specified by a
|
|
matching udev rule.
|
|
|
|
Please direct any comment/question/concern to the linux-hotplug mailing list at:
|
|
linux-hotplug@vger.kernel.org
|
|
|