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= Dracut =
+
= dracut =
  
Dracut is a initramfs infrastructure.
+
'''dracut''' is an event driven initramfs infrastructure. <tt>dracut</tt> (the tool) is used to create an initramfs image by copying tools and files from an installed system and combining it with the dracut framework, usually found in <tt>/usr/lib/dracut/modules.d</tt>.
  
Information about the initial goals and aims can be found at
+
Unlike existing initramfs's, dracut's framework attempts at having as little as possible hard-coded into the initramfs as possible. The initramfs has (basically) one purpose in life -- getting the rootfs mounted so that we can transition to the real rootfs. This is all driven off of device availability. Therefore, instead of scripts hard-coded to do various things, dracut's initramfs depends on udev to create symbolic links to device nodes and then when the rootfs's device node appears, it is mounted and root is switched to it. This helps to keep the time required in the initramfs as little as possible so that things like a 5 second boot aren't made impossible as a result of the very existence of an initramfs.
https://fedoraproject.org/wiki/Initrdrewrite
+
  
Unlike existing initramfs's, this is an attempt at having as little as
+
Most of the initramfs generation functionality in dracut is provided by a bunch of generator modules that are sourced by the main dracut tool to install specific functionality into the initramfs. They live in the modules subdirectory, and use functionality provided by dracut-functions to do their work.
possible hard-coded into the initramfs as possible.  The initramfs has
+
(basically) one purpose in life -- getting the rootfs mounted so that
+
we can transition to the real rootfs.  This is all driven off of
+
device availability.  Therefore, instead of scripts hard-coded to do
+
various things, we depend on udev to create device nodes for us and
+
then when we have the rootfs's device node, we mount and carry on.
+
This helps to keep the time required in the initramfs as little as
+
possible so that things like a 5 second boot aren't made impossible as
+
a result of the very existence of an initramfs.  It's likely that
+
we'll grow some hooks for running arbitrary commands in the flow of
+
the script, but it's worth trying to resist the urge as much as we can
+
as hooks are guaranteed to be the path to slow-down.
+
 
+
Most of the initrd generation functionality in dracut is provided by a bunch
+
of generator modules that are sourced by the main dracut script to install
+
specific functionality into the initrd. They live in the modules subdirectory,
+
and use functionality provided by dracut-functions to do their work.
+
Some general rules for writing modules:
+
* Use one of the inst family of functions to actually install files on to the initrd.  They handle mangling the pathnames and (for binaries, scripts, and kernel modules) installing dependencies as appropriate so you do not have to.
+
* Scripts that end up on the initrd should be POSIX compliant. dracut will try to use /bin/dash as /bin/sh for the initrd if it is available, so you should install it on your system -- dash aims for strict POSIX compliance to the extent possible.
+
* Hooks MUST be POSIX compliant -- they are sourced by the init script, and having a bashism break your user's ability to boot really sucks.
+
* Generator modules should have a two digit numeric prefix -- they run in ascending sort order. Anything in the 90-99 range is stuff that dracut relies on, so try not to break those hooks.
+
* Generator modules and hooks must have a .sh extension.
+
* We have some breakpoints for debugging your hooks.  If you pass 'rd.break rd.shell' as a boot option on the kernel command line, the initramfs will drop to a shell just before switching to a new root. You can pass 'rd.break=hookpoint', and the initramfs will break just before hooks in that hookpoint run. [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracut.kernel] [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#id482827]
+
 
+
Also, there is an attempt to keep things as distribution-agnostic as possible.  Every distribution has their own tool here and it's not something which is really interesting to have separate across them. So contributions to help decrease the distro-dependencies are welcome.
+
  
 
See the [http://git.kernel.org/?p=boot/dracut/dracut.git;a=blob_plain;f=NEWS NEWS] for information about changes in the releases.
 
See the [http://git.kernel.org/?p=boot/dracut/dracut.git;a=blob_plain;f=NEWS NEWS] for information about changes in the releases.
  
;Participate
+
;TROUBLESHOOTING
: See the [wiki:TODO] document for things which still need to be done and [wiki:HACKING] for some
+
: http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#_troubleshooting
: instructions on how to get started.
+
  
;Mailing List
+
;GITTER
: There is also a mailing list that is being used for the discussion -- initramfs <at> vger.kernel.org. It is a typical vger list, send mail to majordomo <at> vger.kernel.org with body of ''subscribe initramfs email <at> host.com''
+
: https://gitter.im/dracutdevs/Lobby
: gmane provides a newsgroup for this mailing list: http://news.gmane.org/gmane.linux.kernel.initramfs/
+
  
 
;IRC
 
;IRC
 
: irc.freenode.net #dracut  
 
: irc.freenode.net #dracut  
 
;GIT
 
: [http://git.kernel.org/?p=boot/dracut/dracut.git git://git.kernel.org/pub/scm/boot/dracut/dracut.git]
 
: [http://git.kernel.org/?p=boot/dracut/dracut.git http://git.kernel.org/pub/scm/boot/dracut/dracut.git]
 
  
 
;Download
 
;Download
Line 55: Line 22:
  
 
;MANPAGES
 
;MANPAGES
: [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracut.man dracut.8]
+
: [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracut8 dracut.8]
: [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracut.kernel dracut.kernel.7]
+
: [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracutkernel7 dracut.kernel.7]
: [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracut.conf dracut.conf.5]
+
: [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracutconf5 dracut.conf.5]
  
 
;Presentation
 
;Presentation
: [http://www.harald-hoyer.de/personal/blog/dracut-talk-on-fosdem-2010 Talk at FOSDEM 2010]
+
: [http://meetings-archive.debian.net/pub/debian-meetings/2010/fosdem10/high/Dracut_a_generic_modular_initramfs_generation_tool.ogv Talk at FOSDEM 2010]
 +
: [http://linuxplumbersconf.org/2009/slides/Harald-Hoyer-dracut.pdf Plumbers 2009 slides]
  
 
;More Documentation
 
;More Documentation
Line 66: Line 34:
  
 
[http://www.ohloh.net/p/dracut Ohloh project page]
 
[http://www.ohloh.net/p/dracut Ohloh project page]
 +
 +
== Origin and Pronunciation of the name Dracut ==
 +
 +
Some people inside Red Hat started to name their projects after cities and villages around the developer headquarters of Red Hat in Westford, Massachusetts.
 +
 +
So, dracut is named after the town [https://www.google.com/maps/place/Dracut,+MA,+USA Dracut], similar to [https://www.google.com/maps/place/Wayland,+MA,+USA Wayland] and [https://www.google.com/maps/place/Weston,+MA,+USA Weston].
 +
 +
According to [http://en.wikipedia.org/wiki/Dracut,_Massachusetts Wikipedia], dracut it is pronounced: /ˈdreɪkət/
 +
 +
== Development ==
 +
 +
;Participate
 +
: See the [wiki:TODO] document for things which still need to be done and [wiki:HACKING] for some
 +
: instructions on how to get started. 
 +
 +
;GIT
 +
: [http://git.kernel.org/cgit/boot/dracut/dracut.git/ git://git.kernel.org/pub/scm/boot/dracut/dracut.git]
 +
: [http://git.kernel.org/cgit/boot/dracut/dracut.git/ http://git.kernel.org/cgit/boot/dracut/dracut.git/]
 +
: [https://github.com/dracutdevs/dracut git@github.com:dracutdevs/dracut.git]
 +
: [https://github.com/dracutdevs/dracut https://github.com/dracutdevs/dracut.git]
 +
 +
;Mailing List
 +
: There is also a mailing list that is being used for the discussion -- initramfs <at> vger.kernel.org. It is a typical vger list, send mail to majordomo <at> vger.kernel.org with body of ''subscribe initramfs email <at> host.com''
 +
: gmane provides a newsgroup for this mailing list: http://news.gmane.org/gmane.linux.kernel.initramfs/
 +
 +
Some general rules for writing modules:
 +
* Use one of the inst family of functions to actually install files on to the initrd.  They handle mangling the pathnames and (for binaries, scripts, and kernel modules) installing dependencies as appropriate so you do not have to.
 +
* Scripts that end up on the initrd should be POSIX compliant. dracut will try to use /bin/dash as /bin/sh for the initrd if it is available, so you should install it on your system -- dash aims for strict POSIX compliance to the extent possible.
 +
* Hooks MUST be POSIX compliant -- they are sourced by the init script, and having a bashism break your user's ability to boot really sucks.
 +
* Generator modules should have a two digit numeric prefix -- they run in ascending sort order. Anything in the 90-99 range is stuff that dracut relies on, so try not to break those hooks.
 +
* Generator modules and hooks must have a .sh extension.
 +
* We have some breakpoints for debugging your hooks.  If you pass 'rd.break rd.shell' as a boot option on the kernel command line, the initramfs will drop to a shell just before switching to a new root. You can pass 'rd.break=hookpoint', and the initramfs will break just before hooks in that hookpoint run. [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#dracut.kernel] [http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#id482827]
 +
 +
Also, there is an attempt to keep things as distribution-agnostic as possible.  Every distribution has their own tool here and it's not something which is really interesting to have separate across them. So contributions to help decrease the distro-dependencies are welcome.

Latest revision as of 07:52, 15 May 2018

[edit] dracut

dracut is an event driven initramfs infrastructure. dracut (the tool) is used to create an initramfs image by copying tools and files from an installed system and combining it with the dracut framework, usually found in /usr/lib/dracut/modules.d.

Unlike existing initramfs's, dracut's framework attempts at having as little as possible hard-coded into the initramfs as possible. The initramfs has (basically) one purpose in life -- getting the rootfs mounted so that we can transition to the real rootfs. This is all driven off of device availability. Therefore, instead of scripts hard-coded to do various things, dracut's initramfs depends on udev to create symbolic links to device nodes and then when the rootfs's device node appears, it is mounted and root is switched to it. This helps to keep the time required in the initramfs as little as possible so that things like a 5 second boot aren't made impossible as a result of the very existence of an initramfs.

Most of the initramfs generation functionality in dracut is provided by a bunch of generator modules that are sourced by the main dracut tool to install specific functionality into the initramfs. They live in the modules subdirectory, and use functionality provided by dracut-functions to do their work.

See the NEWS for information about changes in the releases.

TROUBLESHOOTING
http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html#_troubleshooting
GITTER
https://gitter.im/dracutdevs/Lobby
IRC
irc.freenode.net #dracut
Download
http://www.kernel.org/pub/linux/utils/boot/dracut/
MANPAGES
dracut.8
dracut.kernel.7
dracut.conf.5
Presentation
Talk at FOSDEM 2010
Plumbers 2009 slides
More Documentation
Documentation shipped in the package

Ohloh project page

[edit] Origin and Pronunciation of the name Dracut

Some people inside Red Hat started to name their projects after cities and villages around the developer headquarters of Red Hat in Westford, Massachusetts.

So, dracut is named after the town Dracut, similar to Wayland and Weston.

According to Wikipedia, dracut it is pronounced: /ˈdreɪkət/

[edit] Development

Participate
See the [wiki:TODO] document for things which still need to be done and [wiki:HACKING] for some
instructions on how to get started.
GIT
git://git.kernel.org/pub/scm/boot/dracut/dracut.git
http://git.kernel.org/cgit/boot/dracut/dracut.git/
git@github.com:dracutdevs/dracut.git
https://github.com/dracutdevs/dracut.git
Mailing List
There is also a mailing list that is being used for the discussion -- initramfs <at> vger.kernel.org. It is a typical vger list, send mail to majordomo <at> vger.kernel.org with body of subscribe initramfs email <at> host.com
gmane provides a newsgroup for this mailing list: http://news.gmane.org/gmane.linux.kernel.initramfs/

Some general rules for writing modules:

  • Use one of the inst family of functions to actually install files on to the initrd. They handle mangling the pathnames and (for binaries, scripts, and kernel modules) installing dependencies as appropriate so you do not have to.
  • Scripts that end up on the initrd should be POSIX compliant. dracut will try to use /bin/dash as /bin/sh for the initrd if it is available, so you should install it on your system -- dash aims for strict POSIX compliance to the extent possible.
  • Hooks MUST be POSIX compliant -- they are sourced by the init script, and having a bashism break your user's ability to boot really sucks.
  • Generator modules should have a two digit numeric prefix -- they run in ascending sort order. Anything in the 90-99 range is stuff that dracut relies on, so try not to break those hooks.
  • Generator modules and hooks must have a .sh extension.
  • We have some breakpoints for debugging your hooks. If you pass 'rd.break rd.shell' as a boot option on the kernel command line, the initramfs will drop to a shell just before switching to a new root. You can pass 'rd.break=hookpoint', and the initramfs will break just before hooks in that hookpoint run. [1] [2]

Also, there is an attempt to keep things as distribution-agnostic as possible. Every distribution has their own tool here and it's not something which is really interesting to have separate across them. So contributions to help decrease the distro-dependencies are welcome.

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