README

   1 udev - userspace device management
   2
   3 For more information see the files in the docs/ directory.
   4
   5 Important Note:
   6   Integrating udev in the system is a whole lot of work, has complex dependencies
   7   and differs a lot from distro to distro. All reasonable distros depend on udev
   8   these days and the system will not work without it.
   9
  10   The upstream udev project does not support or recomend to replace a distro's udev
  11   installation with the upstream version. The installation of a unmodified upstream
  12   version may render your system unusable! There is no "default" setup or a set
  13   of "default" rules provided by the upstream udev version.
  14
  15 Requirements:
  16   - 2.6.x version of the Linux kernel. See the RELEASE-NOTES file in the
  17     udev tree and the Documentation/Changes in the kernel source tree for
  18     the actual dependency.
  19
  20   - The kernel must have sysfs and unix domain socket enabled.
  21     (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
  22      but it is completely silly, don't complain if anything goes wrong.)
  23
  24   - The proc filesystem must be mounted on /proc.
  25
  26   - The sysfs filesystem must be mounted at /sys. No other location
  27     will be supported by udev.
  28
  29
  30 Operation:
  31   Udev creates and removes device nodes in /dev, based on events the kernel
  32   sends out on device discovery or removal.
  33
  34   - Early in the boot process, /dev should get a tmpfs filesystem
  35     mounted, which is populated from scratch by udev. Created nodes or
  36     changed permissions will not survive a reboot, which is intentional.
  37
  38   - The content of /lib/udev/devices directory which contains the nodes,
  39     symlinks and directories, which are always expected to be in /dev, should
  40     be copied over to the tmpfs mounted /dev, to provide the required nodes
  41     to initialize udev and continue booting.
  42
  43   - The udevd daemon must be started by an init script to receive netlink
  44     uevents from the kernel driver core.
  45
  46   - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should
  47     be disabled with an init script before actions like loading kernel
  48     modules are taken, which may cause a lot of events.
  49
  50   - All kernel events are matched against a set of specified rules in
  51     /etc/udev/rules.d/ which make it possible to hook into the event
  52     processing to load required kernel modules and setup devices. For all
  53     devices the kernel requests a device node, udev will create one with
  54     the default name or the one specified by a matching udev rules.
  55
  56
  57 Compile Options:
  58   DESTDIR
  59         Prefix of install target, used for package building.
  60   USE_LOG
  61         If set to 'true', udev is able to pass errors or debug information
  62         to syslog. This is very useful to see what udev is doing or not doing.
  63         It is enabled by default, don't expect any useful answer, if you
  64         need to hunt a bug, but you can't enable syslog.
  65   DEBUG
  66         If set to 'true', very verbose debugging messages will be compiled
  67         into the udev binaries. The actual level of debugging is specified
  68         in the udev config file.
  69   STRIPCMD
  70         If udev is compiled for packaging an empty string can be passed
  71         to disable the stripping of the binaries.
  72   USE_SELINUX
  73         If set to 'true', udev will be built with SELinux support
  74         enabled.  This is disabled by default.
  75   USE_KLIBC
  76         If set to 'true', udev is built and linked against klibc.
  77         Default value is 'false'. KLCC specifies the klibc compiler
  78         wrapper, usually located at /usr/bin/klcc.
  79   EXTRAS
  80         If set, will build the "extra" helper programs as specified
  81         as listed (see below for an example).
  82
  83 If you want to build the udev helper programs:
  84   make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
  85
  86
  87 Installation:
  88   - The install target intalls the udev binaries in the default locations,
  89     All at boot time reqired binaries will be installed in /sbin.
  90
  91   - The default location for scripts and binaries that are called from
  92     rules is /lib/udev. Other packages who install udev rules, should use
  93     that directory too.
  94
  95   - It is recommended to use the /lib/udev/devices directory to place
  96     device nodes and symlinks in, which are copied to /dev at every boot.
  97     That way, nodes for broken subsystems or devices which can't be
  98     detected automatically by the kernel, will always be available.
  99
 100   - Copies of the rules files for all major distros are in the etc/udev
 101     directory (you may look there how others distros are doing it).
 102
 103   - The persistent disk links in /dev/disk are the de facto standard
 104     on Linux and should be installed with every default udev installation.
 105     The devfs naming scheme rules are not recommended and not supported.
 106
 107 Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
 108   linux-hotplug-devel@lists.sourceforge.net
 109