X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=21a6c186dc91292d5bf000fcade7be2ef7e9a9ab;hp=fee078898cc2afaad3453bc8b22ceef18d810dcb;hb=0d210b3ad9ebca9fb60c79b2ebbd3d1482485bd3;hpb=c249f66a70f9ea623205f27f7931727acbafba9e diff --git a/README b/README index fee078898..21a6c186d 100644 --- a/README +++ b/README @@ -13,50 +13,55 @@ Important Note: of "default" rules provided by the upstream udev version. Requirements: - - 2.6 version of the Linux kernel. + - 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.) - The proc filesystem must be mounted on /proc. - The sysfs filesystem must be mounted at /sys. No other location - is supported. + will be supported by udev. Operation: - - Udev creates and removes device nodes in /dev based on events - the kernel sends out on device discovery or removal + Udev creates and removes device nodes in /dev, based on events the kernel + sends out on device discovery or removal. - - Directly after mounting the root filesystem, the udevd daemon must be - started by an init script. + - 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. - - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should - be disabled with an init script before kernel modules are loaded. + - 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. - - During bootup, /dev usually gets a tmpfs filesystem mounted which is - populated from scratch by udev (created nodes don't survive a reboot, - the /lib/udev/devices directory should be used for "static nodes"). + - The udevd daemon must be started by an init script to receive netlink + uevents from the kernel driver core. - - Udev replaces the hotplug event management invoked from /sbin/hotplug - by the udevd daemon, which receives the kernel events over netlink. + - 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 which - make it possible to hook into the event processing. + - 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. - - 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). Compile Options: - prefix - Set this to the default root that you want to use only override - this if you really know what you are doing even then, you probably - don't do the right thing. DESTDIR - Prefix for install target, used for package building. + 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. + 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 @@ -75,20 +80,29 @@ Compile Options: 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 program cdrom_id and scsi_id: - make EXTRAS="extras/cdrom_id extras/scsi_id" +If you want to build the udev helper programs: + make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id" + Installation: - - The install target intall the udev binaries in the default locations, - all at boot time reqired binaries will be installed in /sbin. + - 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. + 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. + 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). + + - 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