X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=38459c6b226141408e3b7d2d33c32324dd42c822;hp=6aabf69f8a21376eded9e31e1bc12fa636dfb284;hb=bd59d82322503b796ed6e80425df4bd24b5059ee;hpb=47d9121c9a6a6d4d3415e6a012ebbb3256440a65 diff --git a/README b/README index 6aabf69f8..38459c6b2 100644 --- a/README +++ b/README @@ -7,34 +7,45 @@ 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. +kernel release to work properly. 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. +Never call any private tool in /usr/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 /usr/lib/udev and the entire contents +of the /run/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: + - Version 2.6.34 of the Linux kernel with sysfs, procfs, signalfd, inotify, + unix domain sockets, networking and hotplug enabled + + - Some architectures might need a later kernel, that supports accept4(), + or need to backport the accept4() syscall wiring in the kernel. + + - These options are required: + CONFIG_DEVTMPFS=y CONFIG_HOTPLUG=y - CONFIG_UEVENT_HELPER_PATH="" + CONFIG_INOTIFY_USER=y 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_SYSFS=y + CONFIG_SYSFS_DEPRECATED*=n + CONFIG_UEVENT_HELPER_PATH="" + + - These options might be needed: CONFIG_BLK_DEV_BSG=y (SCSI devices) + CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes) + + - The /dev directory needs the 'devtmpfs' filesystem mounted. + Udev only manages the permissions and ownership of the + kernel-provided device nodes, and possibly creates additional symlinks. - - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option. + - Udev requires /run to be writable, which is usually done by mounting a + 'tmpfs' filesystem. - - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work, - but it is not supported. + - This version of udev does not work properly with the CONFIG_SYSFS_DEPRECATED* + option enabled. - The deprecated hotplug helper /sbin/hotplug should be disabled in the kernel configuration, it is not needed today, and may render the system @@ -45,43 +56,36 @@ Requirements: 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: + - The default rule sset requires 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. - - To build all 'udev extras', libacl, libglib2, libusb, usbutils, pciutils, - and gperf are needed. These dependencies can be disabled with the - --disable-extras configure option. + - Some udev extras have external dependencies like: + libglib2, usbutils, pciutils, and gperf. + All these extras can be disabled with configure options. 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, to apply the configuration to these devices. This is usually done by: - /sbin/udevadm trigger --type=subsystems - /sbin/udevadm trigger --type=devices + During bootup, the events for already existing devices can be replayed, so + that they are configured by udev. The systemd service files contain the + needed commands to start the udev daemon and the coldplug sequence. - - Restarting the daemon does never apply any rules to existing 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. + - New/changed rule files are picked up automatically; there is usually 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. + - Based on events the kernel sends out on device creation/removal, udev + creates/removes device nodes and symlinks in the /dev directory. - 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 + modules to set up 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 + device 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. @@ -90,7 +94,8 @@ Operation: 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. +For more details about udev and udev rules, see the udev man pages: + http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/ Please direct any comment/question to the linux-hotplug mailing list at: linux-hotplug@vger.kernel.org