udev - userspace device management

For more information 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.

Requirements:
  - Version 2.6.22 of the Linux kernel for reliable operation of this release of
    udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.

  - The kernel must have sysfs, unix domain sockets and networking enabled.
    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 kmem
    Especially in LDAP setups, it is required, that getgrnam() is able to resolve
    these group names while no network is available.

Operation:
  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.

  - 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.

  - 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