X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=7f0399e7110e9514e023e0d5fe91ed5c53f622de;hp=9891c696d374c95765dabc307dbb37db57bc106c;hb=cb936a3961f37ccb8eef0c505b8fffa6711c57be;hpb=da4aec2fb4e3c9f1f73a67a5e326c90220fb0c59 diff --git a/README b/README index 9891c696d..7f0399e71 100644 --- a/README +++ b/README @@ -1,107 +1,96 @@ - -udev - a userspace device manager - -For more information on the design, and structure of this project, see the -files in the docs/ directory. - -To use: - -- You must be running a 2.6 version of the Linux kernel. - -- Your 2.6 kernel must have had CONFIG_HOTPLUG enabled when it was built. - -- Make sure sysfs is mounted at /sys. No other location is supported. - You can mount it by running: - mount -t sysfs none /sys - -- Make sure you integrate udev with your hotplug setup. There is a copy of - the rules files for all major distros in the etc/udev folder. You may look - there how others are doing it. - -- Make sure you integrate with the kernel hotplug events. Later versions of - udev are able to listen directly to a netlink socket, older versions used - udevsend to feed the udev daemon with the kernel event. The most basic - setup to run udev is to let the kernel for the udev binary directly: - echo "/sbin/udev" > /proc/sys/kernel/hotplug - - While this may work in some setups, it is not recommended to do. A recent - kernel and udev version is able to operate with the event serializing daemon - udevd, that makes sure, that no "remove" event will beat a "add" event for - the same device. - -- Build the project: - make - - Note: - There are a number of different flags that you can use when building - udev. They are as follows: - prefix - set this to the default root that you want udev to be - installed into. This works just like the 'configure --prefix' - script does. Default value is ''. Only override this if you - really know what you are doing. - USE_KLIBC - if set to 'true', udev is built and linked against the - included version of klibc. Default value is 'false'. - 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.) - USE_SELINUX - if set to 'true', udev will be built with SELinux support - enabled. This is disabled by default. - DEBUG - if set to 'true', debugging messages will be sent to the syslog - as udev is run. 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.) - - So, if you want to build udev using klibc with debugging messages, you - would do: - make USE_KLIBC=true DEBUG=true - - If you want to build the udev helper program cdrom_id and scsi_id you - would do: - make EXTRAS="extras/cdrom_id extras/scsi_id" - - udev will follow the setting of the debug level in udev.conf. Adapt this - value to see the debug in syslog. - -- Install the project: - make install - - This will put the udev binaries in /sbin, create the and /etc/udev - directories, and place the udev configuration files in /etc/udev/. You - will probably want to edit the *.rules files to create custom naming - rules. More info on how the config files are set up are contained in - comments in the files, and is located in the documentation. - -- Add and remove devices from the system and marvel as nodes are created - and removed in /dev based on the device types. - -- If you later get sick of it, uninstall it: - make uninstall - -If nothing seems to happen, make sure your build worked properly by -running the udev-test.pl script as root in the test/ subdirectory of the -udev source tree. Running udevstart should populate an empty /dev -directory. You may test, if a node is recreated after running udevstart. - -Development and documentation help is very much appreciated, see the TODO -file for a list of things left to be done. - -Any comment/questions/concerns please let me and the other udev developers -know by sending a message to the linux-hotplug-devel mailing list at: - linux-hotplug-devel@lists.sourceforge.net - -greg k-h -greg@kroah.com - +udev - Linux userspace device management + +Integrating udev in the system has complex dependencies and may differ from +distribution to distribution. A system may not be able to boot up or work +reliably without a properly installed udev version. The upstream udev project +does not recommend replacing a distro's udev installation with the upstream +version. + +The upstream udev project's set of default rules may require a most recent +kernel release to work properly. This is currently version 2.6.31. + +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. Tools and rules in /lib/udev and the entire contents of +the /dev/.udev directory are private to udev and do change whenever needed. + +Requirements: + - Version 2.6.27 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_INOTIFY_USER=y + CONFIG_SIGNALFD=y + CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes) + CONFIG_BLK_DEV_BSG=y (SCSI devices) + + - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option. + + - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work, + but it is not supported. + + - The deprecated hotplug helper /sbin/hotplug should be disabled in the + kernel configuration, it is not needed today, and may render the system + unusable because the kernel may create too many processes in parallel + so that the system runs out-of-memory. + + - The proc filesystem must be mounted on /proc, and the sysfs filesystem must + be mounted at /sys. No other locations are supported by a standard + udev installation. + + - The system must have the following group names resolvable at udev startup: + disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, and kmem. + Especially in LDAP setups, it is required that getgrnam() be able to resolve + these group names with only the rootfs mounted and while no network is + available. + + - The 'udev extras' has the following dependencies: + libacl, libglib2, libusb, usbutils, pciutils, and gperf. + These dependencies can be disabled with the --disable-extras configure option. + +Setup: + - At bootup, the /dev directory should get the 'devtmpfs' filesystem + mounted. Udev manages the permissions and ownership of the kernel-created + device nodes, and udev possibly creates additional symlinks. If needed, udev also + works on an empty 'tmpfs' filesystem, but some static device nodes like + /dev/null, /dev/console, /dev/kmsg are needed to be able to start udev itself. + + - The udev daemon should be started to handle device events sent by the kernel. + During bootup, the kernel can be asked to send events for all already existing + devices so that they too can be configured by udev. This is usually done by: + /sbin/udevadm trigger --type=subsystems + /sbin/udevadm trigger --type=devices + + - Restarting the daemon never applies any rules to existing devices. + + - New/changed rule files are picked up automatically; there is no daemon + restart or signal needed. + +Operation: + - Udev creates/removes device nodes in /dev, based on events the kernel + sends out on device creation/removal. + + - All kernel events are matched against a set of specified rules, which + possibly hook into the event processing and load required kernel + modules to setup devices. For all devices the kernel exports a major/minor + number; if needed, udev creates a device node with the default kernel + name. If specified, udev applies permissions/ownership to the device + node, creates additional symlinks pointing to the node, and executes + programs to handle the device. + + - The events udev handles, and the information udev merges into its device + database, can be accessed with libudev: + http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/ + http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/ + +For more details about udev and udev rules see the udev(7) man page. + +Please direct any comment/question to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org