X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=c188506b53cd0f6ae77645552351b83f44a5857a;hp=3f4f947f79255816665dd63777da2eee64ec374a;hb=15ff0ba36e9c1f051fe1e35e69f8569d0dfe2d66;hpb=f054627f500450a7aadeaf8a9930354fb268718e diff --git a/README b/README index 3f4f947f7..c188506b5 100644 --- a/README +++ b/README @@ -4,64 +4,102 @@ 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. + and differs a lot from distro to distro. All reasonable distros depend on udev + these days 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 +Requirements: + - 2.6.x version of the Linux kernel. See the RELEASE-NOTES file in the + udev tree and the Documentation/Changes in the kernel source tree for + the actual dependency. - - the kernel must have sysfs, netlink, and hotplug enabled + - The kernel must have sysfs and unix domain socket enabled. + (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work, + but it is completely silly, don't complain if anything goes wrong.) - - proc must be mounted on /proc + - The proc filesystem must be mounted on /proc. - - sysfs must be mounted at /sys, no other location is supported + - The sysfs filesystem must be mounted at /sys. No other location + will be supported by udev. - - 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) +Operation: + Udev creates and removes device nodes in /dev, based on events the kernel + sends out on device discovery or removal. - - udev replaces the hotplug event management invoked from /sbin/hotplug - by the udevd daemon, which receives the kernel events over netlink + - Early in the boot process, /dev 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. - - all kernel events are matched against a set of specified rules which - make it posible to hook into the event processing + - 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. - - 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) + - The udevd daemon must be started by an init script to receive netlink + uevents from the kernel driver core. -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 + - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should + be disabled with an init script before actions like loading kernel + modules are taken, which may cause a lot of events. + + - 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 requests a device node, udev will create one with + the default name or the one specified by a matching udev rules. + + +Compile Options: DESTDIR - prefix for install target for package building + Prefix of install target, used 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. + 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', verbose debugging messages will be compiled into - the udev binaries. Default value is 'false'. + 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 + 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 klibc. + If set to 'true', udev is built and linked against klibc. Default value is 'false'. KLCC specifies the klibc compiler - wrapper, usually in /usr/bin/klcc + wrapper, usually located at /usr/bin/klcc. EXTRAS - if set, will build the "extra" helper programs as specified - as listed (see below for an example.) + If set, will build the "extra" helper programs as specified + as listed (see below for an example). + +If you want to build the udev helper programs: + make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id" + + +Installation: + - The install target intalls the udev binaries in the default locations, + All at boot time reqired binaries will be installed in /sbin. + + - The default location for scripts and binaries that are called from + rules is /lib/udev. Other packages who install udev rules, should 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. + + - Copies of the rules files for all major distros are in the etc/udev + directory (you may look there how others distros are doing it). -if you want to build the udev helper program cdrom_id and scsi_id: - make EXTRAS="extras/cdrom_id extras/scsi_id" + - The persistent disk links in /dev/disk are the de facto standard + on Linux and should be installed with every default udev installation. + The devfs naming scheme rules are not recommended and not supported. Please direct any comment/question/concern to the linux-hotplug-devel mailing list at: linux-hotplug-devel@lists.sourceforge.net