X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=591e03a057a96a0d244ba5e3978c42b43f642c70;hp=fffa7939879a1d814d30425490715dcb907c4497;hb=b02140b6bcd080c5fd60306a493447ce7afdad64;hpb=e1b579406db58dc4ced1bec6339f7647c4fd69ea diff --git a/README b/README index fffa79398..591e03a05 100644 --- a/README +++ b/README @@ -1,61 +1,75 @@ - -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 - -- 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 - 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_INOTIFY=y + CONFIG_SIGNALFD=y + CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes) + CONFIG_BLK_DEV_BSG=y (SCSI tape devices) + + - 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