README

   1 dracut
   2 ------
   3 dracut is an event driven initramfs infrastructure.
   4
   5 dracut (the tool) is used to create an initramfs image by copying tools
   6 and files from an installed system and combining it with the
   7 dracut framework, usually found in /usr/lib/dracut/modules.d.
   8
   9 Unlike existing initramfs's, this is an attempt at having as little as
  10 possible hard-coded into the initramfs as possible.  The initramfs has
  11 (basically) one purpose in life -- getting the rootfs mounted so that
  12 we can transition to the real rootfs.  This is all driven off of
  13 device availability.  Therefore, instead of scripts hard-coded to do
  14 various things, we depend on udev to create device nodes for us and
  15 then when we have the rootfs's device node, we mount and carry on.
  16 This helps to keep the time required in the initramfs as little as
  17 possible so that things like a 5 second boot aren't made impossible as
  18 a result of the very existence of an initramfs.  It's likely that
  19 we'll grow some hooks for running arbitrary commands in the flow of
  20 the script, but it's worth trying to resist the urge as much as we can
  21 as hooks are guaranteed to be the path to slow-down.
  22
  23 Most of the initramfs generation functionality in dracut is provided by a bunch
  24 of generator modules that are sourced by the main dracut script to install
  25 specific functionality into the initramfs.  They live in the modules.d
  26 subdirectory, and use functionality provided by dracut-functions to do their
  27 work.
  28
  29 Some general rules for writing modules:
  30  * Use one of the inst family of functions to actually install files
  31    on to the initramfs.  They handle mangling the pathnames and (for binaries,
  32    scripts, and kernel modules) installing dependencies as appropriate so
  33    you do not have to.
  34  * Scripts that end up on the initramfs should be POSIX compliant. dracut
  35    will try to use /bin/dash as /bin/sh for the initramfs if it is available,
  36    so you should install it on your system -- dash aims for strict POSIX
  37    compliance to the extent possible.
  38  * Hooks MUST be POSIX compliant -- they are sourced by the init script,
  39    and having a bashism break your user's ability to boot really sucks.
  40  * Generator modules should have a two digit numeric prefix -- they run in
  41    ascending sort order. Anything in the 90-99 range is stuff that dracut
  42    relies on, so try not to break those hooks.
  43  * Hooks must have a .sh extension.
  44  * Generator modules are described in more detail in README.modules.
  45  * We have some breakpoints for debugging your hooks.  If you pass 'rdbreak'
  46    as a kernel parameter, the initramfs will drop to a shell just before
  47    switching to a new root. You can pass 'rdbreak=hookpoint', and the initramfs
  48    will break just before hooks in that hookpoint run.
  49
  50 Also, there is an attempt to keep things as distribution-agnostic as
  51 possible.  Every distribution has their own tool here and it's not
  52 something which is really interesting to have separate across them.
  53 So contributions to help decrease the distro-dependencies are welcome.
  54
  55 Currently dracut lives on github.com and kernel.org.
  56
  57 The tarballs can be found here:
  58         http://www.kernel.org/pub/linux/utils/boot/dracut/
  59         ftp://ftp.kernel.org/pub/linux/utils/boot/dracut/
  60
  61 Git:
  62         git://git.kernel.org/pub/scm/boot/dracut/dracut.git
  63         http://git.kernel.org/pub/scm/boot/dracut/dracut.git
  64         https://git.kernel.org/pub/scm/boot/dracut/dracut.git
  65
  66         git@github.com:dracutdevs/dracut.git
  67
  68 Git Web:
  69         https://github.com/dracutdevs/dracut.git
  70
  71         http://git.kernel.org/?p=boot/dracut/dracut.git
  72
  73 Project Documentation:
  74         http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html
  75
  76 Project Wiki:
  77         http://dracut.wiki.kernel.org
  78
  79 See the TODO file for things which still need to be done and HACKING for
  80 some instructions on how to get started.  There is also a mailing list
  81 that is being used for the discussion -- initramfs@vger.kernel.org.
  82 It is a typical vger list, send mail to majordomo@vger.kernel.org with body
  83 of 'subscribe initramfs email@host.com'
  84
  85
  86 Licensed under the GPLv2