udev - userspace device management
-For more information see the files in the docs/ directory.
+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.
-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.
+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 2.6.18 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.
-
- - 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.)
-
- - The proc filesystem must be mounted on /proc, the sysfs filesystem must
- be mounted at /sys. No other locations are supported by udev.
-
+ - 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
+ Udev creates and removes device nodes in /dev/, based on events the kernel
sends out on device discovery or removal.
- - 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.
+ - 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,
+ - 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 on bootup, before
- actions like loading kernel modules are taken, which may cause a lot of
- events.
-
- - The udevd daemon must be started on bootup to receive netlink uevents
- from the kernel driver core.
+ - 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
device node with the default kernel name, or the one specified by a
matching udev rule.
-
-Compile Options:
- DESTDIR
- Prefix of install target, used for package building.
- USE_LOG
- If set to 'true', udev is able to pass errors or debug information
- to syslog. This is very useful to see what udev is doing or not doing.
- It is enabled by default, don't expect any useful answer, if you
- need to hunt a bug, but you can't enable syslog.
- DEBUG
- If set to 'true', very verbose debugging messages will be compiled
- into the udev binaries. The actual level of debugging is specified
- in the udev config file.
- USE_SELINUX
- If set to 'true', udev will be built with SELinux support
- enabled. This is disabled by default.
- EXTRAS
- list of helper programs in extras/ to build.
- make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
-
-
-Installation:
- - The install target intalls the udev binaries in the default locations,
- All binaries will be installed in /lib/udev or /sbin.
-
- - The default location for scripts and binaries that are called from
- rules is /lib/udev. Other packages who install udev rules, may use
- that directory too.
-
- - It is recommended to use the /lib/udev/devices/ directory to place
- device nodes and symlinks in, which are copied to /dev at every boot.
- That way, nodes for broken subsystems or devices which can't be
- detected automatically by the kernel, will always be available.
-
- - Default udev rules and persistent device naming rules are required by other
- software that depends on the data udev collects from the devices,
- and should be installed by default with every udev installation.
-
-Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
+Please direct any comment/question/concern to the linux-hotplug mailing list at:
linux-hotplug@vger.kernel.org
~ianmdlvl / elogind.git / blobdiff