X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=f37c12a8e06b65008481afb5b2bc66220237e6a8;hp=19ed4468eab0806207bacf6f27dc3f606413789a;hb=98520be72f9a0167df1da3c7b1a4ca2e88c3c831;hpb=c2df8b5f517216ab7763c1b25655c170cfcee097 diff --git a/README b/README index 19ed4468e..f37c12a8e 100644 --- a/README +++ b/README @@ -3,75 +3,92 @@ 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. + 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. - 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. +Requirements: + - Version 2.6.15 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. -udev requires: - - 2.6 version of the Linux kernel + - 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 is completely silly - don't complain if anything goes wrong.) - - the kernel must have sysfs, netlink, and hotplug enabled + - The proc filesystem must be mounted on /proc, the sysfs filesystem must + be mounted at /sys. No other location is supported by udev. - - proc must be mounted on /proc - - sysfs must be mounted at /sys, no other location is supported +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 + - 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. - - 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) + - 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. - - udev replaces the hotplug event management invoked from /sbin/hotplug - by the udevd daemon, which receives the kernel events over netlink + - 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. - - all kernel events are matched against a set of specified rules which - make it posible to hook into the event processing + - The udevd daemon must be started on bootup to receive netlink uevents + from the kernel driver core. - - 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) + - 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. -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 + +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. Note, if you - are building udev against klibc it is recommended that you - disable this option (due to klibc's syslog implementation.) + 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 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.) + 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 at boot time reqired 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, 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. -if you want to build udev using klibc with debugging messages: - make USE_KLIBC=true DEBUG=true + - Copies of the rules files for the major distros are provided as examples + in the etc/udev directory. -if you want to build the udev helper program cdrom_id and scsi_id: - make EXTRAS="extras/cdrom_id extras/scsi_id" + - The persistent device naming links in /dev/disk/ are required by other + software that depends on the data udev has collected 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-devel@lists.sourceforge.net + linux-hotplug@vger.kernel.org