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udev - userspace device management
For more information see the files in the docs/ directory.
Important Note:
Integrating udev in the system is a whole lot of work, has complex dependencies
and differs a lot from distro to distro. All reasonable distros use udev these
days, the major ones make it mandatory and the system will not work without it.
The upstream udev project does not support or recomend to replace a distro's udev
installation with the upstream version. The installation of a unmodified upstream
version may render your system unusable! There is no "default" setup or a set
of "default" rules provided by the upstream udev version.
udev requires:
- 2.6 version of the Linux kernel
- the kernel must have sysfs, netlink, and hotplug enabled
- proc must be mounted on /proc
- sysfs must be mounted at /sys, no other location is supported
- udev creates and removes device nodes in /dev based on events
the kernel sends out on device discovery or removal
- during bootup /dev usually gets a tmpfs mounted which is populated scratch
by udev (created nodes don't survive a reboot, it always starts from scratch)
- udev replaces the hotplug event management invoked from /sbin/hotplug
by the udevd daemon, which receives the kernel events over netlink
- all kernel events are matched against a set of specified rules which
make it posible to hook into the event processing
- there is a copy of the rules files for all major distros in the etc/udev
directory (you may look there how others distros are doing it)
Setting which are used for building udev:
prefix
set this to the default root that you want to use
Only override this if you really know what you are doing
DESTDIR
prefix for install target for package building
USE_LOG
if set to 'true', udev will emit messages to the syslog when
it creates or removes device nodes. This is helpful to see
what udev is doing. This is enabled by default. Note, if you
are building udev against klibc it is recommended that you
disable this option (due to klibc's syslog implementation.)
DEBUG
if set to 'true', verbose debugging messages will be compiled into
the udev binaries. Default value is 'false'.
USE_SELINUX
if set to 'true', udev will be built with SELinux support
enabled. This is disabled by default.
USE_KLIBC
if set to 'true', udev is built and linked against the
included version of klibc. Default value is 'false'.
KERNEL_DIR
If this is not set it will default to /lib/modules/`uname -r`/build
This is used if USE_KLIBC=true to find the kernel include
directory that klibc needs to build against. This must be set
if you are not building udev while running a 2.6 kernel.
EXTRAS
if set, will build the "extra" helper programs as specified
as listed (see below for an example.)
if you want to build udev using klibc with debugging messages:
make USE_KLIBC=true DEBUG=true
if you want to build the udev helper program cdrom_id and scsi_id:
make EXTRAS="extras/cdrom_id extras/scsi_id"
Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
linux-hotplug-devel@lists.sourceforge.net
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