X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=a76583ababfed3434e961a9c8a125b5c1e9e9033;hp=139c6e1a6ff00e77052a0e9b4bd6093b799ee25e;hb=a4a2edb0ead43ae5bae63ca8c2a7ad162016372f;hpb=34c00c915c6dd9d063551732169cb3c3126376ad diff --git a/README b/README index 139c6e1a6..a76583aba 100644 --- a/README +++ b/README @@ -1,99 +1,53 @@ +udev - userspace device management -udev - a userspace device manager +For more information see the files in the docs/ directory. -For more information on the design, and structure of this project, see the -files in the docs/ directory. +Important Note: + 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. -To use: +Requirements: + - Version 2.6.19 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. -- You must be running a 2.6 version of the Linux kernel. + - 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 does not make any sense - don't complain if anything goes wrong.) -- Your 2.6 kernel must have had CONFIG_HOTPLUG enabled when it was built. + - The proc filesystem must be mounted on /proc/, the sysfs filesystem must + be mounted at /sys/. No other locations are supported by udev. -- 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. +Operation: + Udev creates and removes device nodes in /dev/, based on events the kernel + sends out on device discovery or removal. -- 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 + - 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. - 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. + - 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. -- Build the project: - make + - 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. - 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. + - The udevd daemon must be started on bootup to receive netlink uevents + from the kernel driver core. - So, if you want to build udev using klibc with debugging messages, you - would do: - make USE_KLIBC=true DEBUG=true + - 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. - 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. - -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 +Please direct any comment/question/concern to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org