README.md

   1 dracut
   2 ====
   3
   4 dracut is an event driven initramfs infrastructure.
   5
   6 [![Build Status](https://travis-ci.org/dracutdevs/dracut.svg?branch=master)](https://travis-ci.org/dracutdevs/dracut)
   7
   8 dracut (the tool) is used to create an initramfs image by copying tools
   9 and files from an installed system and combining it with the
  10 dracut framework, usually found in /usr/lib/dracut/modules.d.
  11
  12 Unlike existing initramfs's, this is an attempt at having as little as
  13 possible hard-coded into the initramfs as possible.  The initramfs has
  14 (basically) one purpose in life -- getting the rootfs mounted so that
  15 we can transition to the real rootfs.  This is all driven off of
  16 device availability.  Therefore, instead of scripts hard-coded to do
  17 various things, we depend on udev to create device nodes for us and
  18 then when we have the rootfs's device node, we mount and carry on.
  19 This helps to keep the time required in the initramfs as little as
  20 possible so that things like a 5 second boot aren't made impossible as
  21 a result of the very existence of an initramfs.  It's likely that
  22 we'll grow some hooks for running arbitrary commands in the flow of
  23 the script, but it's worth trying to resist the urge as much as we can
  24 as hooks are guaranteed to be the path to slow-down.
  25
  26 Most of the initramfs generation functionality in dracut is provided by a bunch
  27 of generator modules that are sourced by the main dracut script to install
  28 specific functionality into the initramfs.  They live in the modules.d
  29 subdirectory, and use functionality provided by dracut-functions to do their
  30 work.
  31
  32 Some general rules for writing modules:
  33  * Use one of the inst family of functions to actually install files
  34    on to the initramfs.  They handle mangling the pathnames and (for binaries,
  35    scripts, and kernel modules) installing dependencies as appropriate so
  36    you do not have to.
  37  * Scripts that end up on the initramfs should be POSIX compliant. dracut
  38    will try to use /bin/dash as /bin/sh for the initramfs if it is available,
  39    so you should install it on your system -- dash aims for strict POSIX
  40    compliance to the extent possible.
  41  * Hooks MUST be POSIX compliant -- they are sourced by the init script,
  42    and having a bashism break your user's ability to boot really sucks.
  43  * Generator modules should have a two digit numeric prefix -- they run in
  44    ascending sort order. Anything in the 90-99 range is stuff that dracut
  45    relies on, so try not to break those hooks.
  46  * Hooks must have a .sh extension.
  47  * Generator modules are described in more detail in README.modules.
  48  * We have some breakpoints for debugging your hooks.  If you pass 'rdbreak'
  49    as a kernel parameter, the initramfs will drop to a shell just before
  50    switching to a new root. You can pass 'rdbreak=hookpoint', and the initramfs
  51    will break just before hooks in that hookpoint run.
  52
  53 Also, there is an attempt to keep things as distribution-agnostic as
  54 possible.  Every distribution has their own tool here and it's not
  55 something which is really interesting to have separate across them.
  56 So contributions to help decrease the distro-dependencies are welcome.
  57
  58 Currently dracut lives on github.com and kernel.org.
  59
  60 The tarballs can be found here:
  61         http://www.kernel.org/pub/linux/utils/boot/dracut/
  62         ftp://ftp.kernel.org/pub/linux/utils/boot/dracut/
  63
  64 Git:
  65         git://git.kernel.org/pub/scm/boot/dracut/dracut.git
  66         http://git.kernel.org/pub/scm/boot/dracut/dracut.git
  67         https://git.kernel.org/pub/scm/boot/dracut/dracut.git
  68
  69         git@github.com:dracutdevs/dracut.git
  70
  71 Git Web:
  72         https://github.com/dracutdevs/dracut.git
  73
  74         http://git.kernel.org/?p=boot/dracut/dracut.git
  75
  76 Project Documentation:
  77         http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html
  78
  79 Project Wiki:
  80         http://dracut.wiki.kernel.org
  81
  82 See the TODO file for things which still need to be done and HACKING for
  83 some instructions on how to get started.  There is also a mailing list
  84 that is being used for the discussion -- initramfs@vger.kernel.org.
  85 It is a typical vger list, send mail to majordomo@vger.kernel.org with body
  86 of 'subscribe initramfs email@host.com'
  87
  88
  89 Licensed under the GPLv2