X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=2cde586ce23ddcc0ec15cc0b653cf6b7fb18d240;hp=3f4f947f79255816665dd63777da2eee64ec374a;hb=72a157b9ad240a075d0a6936168a297df51e3c50;hpb=a8349b33e564f7faa83341cb1fa58466b0589ae9 diff --git a/README b/README index 3f4f947f7..2cde586ce 100644 --- a/README +++ b/README @@ -3,66 +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 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 2.6.18 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. -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 does not make any sense - 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 locations are 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 + /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. -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. - 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 klibc. - Default value is 'false'. KLCC specifies the klibc compiler - wrapper, usually in /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" - -Please direct any comment/question/concern to the linux-hotplug-devel mailing list at: - linux-hotplug-devel@lists.sourceforge.net +Please direct any comment/question/concern to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org