X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=3a511802eadbea08b3343c5303d938e4337e30aa;hp=fe56095686f7c1e906cdf7e9b81abd88be152bf5;hb=a8aab0e95b18c772c91104c02a283d03180ff19f;hpb=dfc9761d8846a5f6f437fb599bc6817d14efbec2 diff --git a/README b/README index fe5609568..3a511802e 100644 --- a/README +++ b/README @@ -3,110 +3,68 @@ 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.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 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 - will be supported by udev. - + - Version 2.6.25 of the Linux kernel with sysfs, procfs, signalfd, inotify, + unix domain sockets, networking and hotplug enabled: + CONFIG_HOTPLUG=y + CONFIG_UEVENT_HELPER_PATH="" + CONFIG_NET=y + CONFIG_UNIX=y + CONFIG_SYSFS=y + CONFIG_SYSFS_DEPRECATED*=n + CONFIG_PROC_FS=y + CONFIG_TMPFS=y + CONFIG_TMPFS_POSIX_ACL=y + CONFIG_INOTIFY=y + CONFIG_SIGNALFD=y + + - For reliable operation, the kernel must not use the CONFIG_SYSFS_DEPRECATED* + option. + + - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not + supported. + + - The proc filesystem must be mounted on /proc/, the sysfs filesystem must + be mounted at /sys/. No other locations are supported by udev. + + - The system must have the following group names resolvable at udev startup: + disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem. + Especially in LDAP setups, it is required, that getgrnam() is able to resolve + these group names with only the rootfs mounted, and while no network is + available. + + - To build all udev extras, libacl, libglib2, libusb, usbutils, pciutils are + needed. These dependencies can be disabled with the --disable-extras option. Operation: - Udev creates and removes device nodes in /dev, based on events the kernel + Udev creates and removes device nodes in /dev/, based on events the kernel sends out on device discovery or removal. - - Directly after mouting the real root filesystem, wherever that - happens, in initramfs or with a directly mounted root, /dev should get - a tmpfs filesystem mounted, which is populated from scratch by udev. - Created nodes or changed permissions don't survive a reboot. - - - The content of /lib/udev/devices directory should be copied over to the - tmpfs mounted /dev, to provide the required nodes to initialize udev. + - Early in the boot process, the /dev/ directory should get a 'tmpfs' + filesystem mounted, which is maintained by udev. Created nodes or changed + permissions will not survive a reboot, which is intentional. - - The udevd daemon must be started to receive netlink events from the kernel - driver core. + - 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. - - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should - be disabled with an init script before the boot scripts are run and - kernel modules are loaded. + - The old hotplug helper /sbin/hotplug should be disabled in the kernel + configuration, it is not needed, and may render the system unusable + because of a fork-bombing behavior. - 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 + /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 requests a device node, udev will create one with - the default name or the one specified by a matching udev rules. - - -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, 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 - 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 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 diretory 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). - - - 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. + 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-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