mirror of
https://github.com/systemd/systemd.git
synced 2024-12-26 03:22:00 +03:00
92 lines
4.0 KiB
Plaintext
92 lines
4.0 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 2.6.18 of the Linux kernel for reliable operation of this release of
|
|
udev. The kernel may have a requirement on udev too, see Documentation/Changes
|
|
in the kernel source tree for the actual dependency.
|
|
|
|
- The kernel must have sysfs, unix domain sockets and networking enabled.
|
|
(unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
|
|
but it does not make any sense - don't complain if anything goes wrong.)
|
|
|
|
- The proc filesystem must be mounted on /proc, the sysfs filesystem must
|
|
be mounted at /sys. No other locations are supported by udev.
|
|
|
|
|
|
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
|
|
/etc/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.
|
|
|
|
|
|
Compile Options:
|
|
DESTDIR
|
|
Prefix of install target, used for package building.
|
|
USE_LOG
|
|
If set to 'true', udev is able to pass errors or debug information
|
|
to syslog. This is very useful to see what udev is doing or not doing.
|
|
It is enabled by default, don't expect any useful answer, if you
|
|
need to hunt a bug, but you can't enable syslog.
|
|
DEBUG
|
|
If set to 'true', very verbose debugging messages will be compiled
|
|
into the udev binaries. The actual level of debugging is specified
|
|
in the udev config file.
|
|
USE_SELINUX
|
|
If set to 'true', udev will be built with SELinux support
|
|
enabled. This is disabled by default.
|
|
EXTRAS
|
|
list of helper programs in extras/ to build.
|
|
make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
|
|
|
|
|
|
Installation:
|
|
- The install target intalls the udev binaries in the default locations,
|
|
All binaries will be installed in /lib/udev or /sbin.
|
|
|
|
- The default location for scripts and binaries that are called from
|
|
rules is /lib/udev. Other packages who install udev rules, may use
|
|
that directory too.
|
|
|
|
- It is recommended to use the /lib/udev/devices/ directory to place
|
|
device nodes and symlinks in, which are copied to /dev at every boot.
|
|
That way, nodes for broken subsystems or devices which can't be
|
|
detected automatically by the kernel, will always be available.
|
|
|
|
- Default udev rules and persistent device naming rules are required by other
|
|
software that depends on the data udev collects from the devices,
|
|
and should be installed by default with every udev installation.
|
|
|
|
Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
|
|
linux-hotplug@vger.kernel.org
|
|
|