X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=b4c0ee051faa4f014b6fb454ea7b999d2326b7db;hp=9891c696d374c95765dabc307dbb37db57bc106c;hb=456719b6f941d917e7c9444fa6149f35a188d785;hpb=da4aec2fb4e3c9f1f73a67a5e326c90220fb0c59 diff --git a/README b/README index 9891c696d..b4c0ee051 100644 --- a/README +++ b/README @@ -1,107 +1,74 @@ - -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 - userspace device management + +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. + +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 +/dev/.udev/ is private to udev. + +Requirements: + - 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 + sends out on device discovery or removal. + + - 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, + 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 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 + /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. + +Please direct any comment/question/concern to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org