X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=78787469cca29f29359cbe2a661f94cd2fcae8df;hp=94a397936e5e7989a5e31ccfcfc44206512e1d28;hb=0c0b3f97cad4c34140dda3aa85a9bc74badb4b16;hpb=7d27ce1dc005b3972ab7ed77a86f6333c2f8ee9f diff --git a/README b/README index 94a397936..78787469c 100644 --- a/README +++ b/README @@ -1,82 +1,96 @@ - -udev - a userspace implementation of devfs - -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. - -- Make sure sysfs is mounted. udev will figure out where sysfs is mounted, but - the traditional place for it is at /sys. You can mount it by hand by running: - mount -t sysfs none /sys - -- Make sure you have the latest version of the linux-hotplug scripts. They are - available at linux-hotplug.sf.net or from your local kernel.org mirror at: - kernel.org/pub/linux/utils/kernel/hotplug/ - They are required in order for udev to work properly. - - If for some reason you do not install the hotplug scripts, you must tell the - kernel to point the hotplug binary at wherever you install udev at. This can - be done by: - echo "/sbin/udev" > /proc/sys/kernel/hotplug - -- 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. - KLIBC - if set to 'true', udev is built and linked against the included - version of klibc. Default value is 'false'. - DEBUG - if set to 'true', debugging messages will be sent to the syslog - as udev is run. Default value is 'false'. - DBUS - if set to 'true', DBUS messages will be sent everytime udev - creates or removes a device node. This requires that DBUS - development headers and libraries be present on your system to - build properly. Default value is 'false'. - - So, if you want to build udev using klibc with debugging messages, you - would do: - make KLIBC=true DEBUG=true - - -- Install the project: - make install - - This will put the udev binary in /sbin, create the /udev and /etc/udev - directories, and place the udev configuration files in /etc/udev. You - will probably want to edit the namedev.* 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 /udev/ based on the device types. - -- If you later get sick of it, uninstall it: - make uninstall - - -Things are still quite rough, and it's a bit beyond proof of concept -code. Help is very much appreciated, see the TODO file for a list of -things left to be done. - -If you want to build using klibc, use the Makefile.klibc file: - - read the klibc/klibc/README file for how to set up the linux - symlink properly. - - make clean - - make -f Makefile.klibc -and marvel at the tiny binary you just created :) - -Any comment/questions/concerns please let me know. - -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 to replace 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 content of +the /dev/.udev directory is private to udev and does 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 will 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, 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, 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 configure option. + +Setup: + - At bootup, the /dev directory should get the 'devtmpfs' filesystem + mounted. Udev will manage permissions and ownership of the kernel-created + device nodes, and possibly create 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, to apply the configuration to these devices. This is usually done by: + /sbin/udevadm trigger --type=subsystems + /sbin/udevadm trigger --type=devices + + - Restarting the daemon does never apply 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 will create 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