X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=2cde586ce23ddcc0ec15cc0b653cf6b7fb18d240;hp=fee078898cc2afaad3453bc8b22ceef18d810dcb;hb=21a6e5940d1c3e9299e398fc224f3b864397744e;hpb=c249f66a70f9ea623205f27f7931727acbafba9e diff --git a/README b/README index fee078898..2cde586ce 100644 --- a/README +++ b/README @@ -3,93 +3,51 @@ 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 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. + 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: - - 2.6 version of the Linux kernel. - - - The kernel must have sysfs, netlink, and hotplug enabled. + - 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 proc filesystem must be mounted on /proc. + - 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 sysfs filesystem must be mounted at /sys. No other location - is supported. + - 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 - - - Directly after mounting the root filesystem, the udevd daemon must be - started by an init script. - - - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should - be disabled with an init script before kernel modules are loaded. - - - 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"). - - - 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 possible to hook into the event processing. - - - 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. - 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. - 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. - STRIPCMD - If udev is compiled for packaging an empty string can be passed - to disable the stripping of the binaries. - 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 klibc. - Default value is 'false'. KLCC specifies the klibc compiler - 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 you want to build the udev helper program cdrom_id and scsi_id: - make EXTRAS="extras/cdrom_id extras/scsi_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 default location for scripts and binaries that are called from - rules is /lib/udev. - - - 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. - -Please direct any comment/question/concern to the linux-hotplug-devel mailing list at: - linux-hotplug-devel@lists.sourceforge.net + 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