-
-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.
-
-- Your 2.6 kernel must have had CONFIG_HOTPLUG enabled when it was built.
-
-- 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.
- USE_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'.
- USE_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 USE_KLIBC=true DEBUG=true
-
- Note: If you want to use klibc, you will have to set up the "linux"
- symlink properly. See the file klibc/klibc/README and pay
- attention to step "a)" there.
-
-- 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, but it should work properly. 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
-
-
-
+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 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 2.6.32.
+
+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.
+
+Requirements:
+ - 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 needed:
+ 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_INOTIFY_USER=y
+ CONFIG_SIGNALFD=y
+
+ - These options might be needed:
+ CONFIG_TMPFS=y
+ CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+ CONFIG_BLK_DEV_BSG=y (SCSI devices)
+
+ - Udev does 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, and the sysfs filesystem must
+ be mounted at /sys. No other locations are supported by a standard
+ udev installation.
+
+ - 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.
+
+ - Some udev extras have external dependencies like:
+ libacl, libglib2, libusb, 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 so that they too can be configured by udev. This is usually done by:
+ /sbin/udevadm trigger --type=subsystems
+ /sbin/udevadm trigger --type=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.
+
+Operation:
+ - Based on events the kernel sends out on device creation/removal, udev
+ creates/removes device nodes 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 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
+ 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 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
~ianmdlvl / elogind.git / blobdiff