X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=a2f00021e8b58e57fd0c1239244c6bf9ab9e49bd;hp=74aa7901cf467e005a4eb2ac27560611f31528b4;hb=0f50d0ef04feecfb33ac7dd7a38300679c3ed27d;hpb=15c02d46f5b7061808c5d37753a2e6cb90f472c8 diff --git a/README b/README index 74aa7901c..a2f00021e 100644 --- a/README +++ b/README @@ -1,97 +1,74 @@ udev - userspace device management -For more information see the files in the docs/ directory. +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. -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 major distros depend on udev these - days and the system may not work without a proper installed version. The upstream - udev project does not support or recommend to replace a distro's udev installation - with the upstream version. The installation of a unmodified upstream version may - render your system unusable. Until now, there is no "default" setup or a set of - "default" rules provided by the upstream udev version. +Tools and rules shipped by udev are not public API and may change at any time. +Never call any private tool in /lib/udev from any external application, it might +just go away in the next release. Access to udev information is only offered +by udevadm and libudev. Everything in /lib/udev and /dev/.udev/ is 100% private +to udev. 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. - - - 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 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, + gperf 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. - - 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. + - 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 content of /lib/udev/devices directory which contains the nodes, + - 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. + - 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 exports a major/minor number, udev will create a - device node with the default kernel name or the one specified by a + device node with the default kernel name, or the one specified by a matching udev rule. - -Compile Options: - DESTDIR - 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, 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. - USE_SELINUX - If set to 'true', udev will be built with SELinux support - enabled. This is disabled by default. - EXTRAS - 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. - - - Copies of the rules files for the major distros are provided as examples - in the etc/udev directory. - - - 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 +Please direct any comment/question/concern to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org