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dracut
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====
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dracut is an event driven initramfs infrastructure.
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[](https://travis-ci.org/dracutdevs/dracut)
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[](https://github.com/dracutdevs/dracut/actions?query=workflow%3AFedora-31)
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[](https://github.com/dracutdevs/dracut/actions?query=workflow%3AFedora-32)
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dracut (the tool) is used to create an initramfs image by copying tools
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and files from an installed system and combining it with the
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dracut framework, usually found in /usr/lib/dracut/modules.d.
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Unlike other implementations, dracut hard-codes as little
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as possible into the initramfs. The initramfs has
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(basically) one purpose in life -- getting the rootfs mounted so that
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we can transition to the real rootfs. This is all driven off of
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device availability. Therefore, instead of scripts hard-coded to do
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various things, we depend on udev to create device nodes for us and
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then when we have the rootfs's device node, we mount and carry on.
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This helps to keep the time required in the initramfs as little as
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possible so that things like a 5 second boot aren't made impossible as
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a result of the very existence of an initramfs.
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Most of the initramfs generation functionality in dracut is provided by a bunch
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of generator modules that are sourced by the main dracut script to install
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specific functionality into the initramfs. They live in the modules.d
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subdirectory, and use functionality provided by dracut-functions to do their
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work.
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Some general rules for writing modules:
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* Use one of the inst family of functions to actually install files
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on to the initramfs. They handle mangling the pathnames and (for binaries,
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scripts, and kernel modules) installing dependencies as appropriate so
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you do not have to.
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* Scripts that end up on the initramfs should be POSIX compliant. dracut
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will try to use /bin/dash as /bin/sh for the initramfs if it is available,
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so you should install it on your system -- dash aims for strict POSIX
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compliance to the extent possible.
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* Hooks MUST be POSIX compliant -- they are sourced by the init script,
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and having a bashism break your user's ability to boot really sucks.
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* Generator modules should have a two digit numeric prefix -- they run in
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ascending sort order. Anything in the 90-99 range is stuff that dracut
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relies on, so try not to break those hooks.
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* Hooks must have a .sh extension.
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* Generator modules are described in more detail in README.modules.
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* We have some breakpoints for debugging your hooks. If you pass 'rdbreak'
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as a kernel parameter, the initramfs will drop to a shell just before
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switching to a new root. You can pass 'rdbreak=hookpoint', and the initramfs
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will break just before hooks in that hookpoint run.
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Also, there is an attempt to keep things as distribution-agnostic as
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possible. Every distribution has their own tool here and it's not
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something which is really interesting to have separate across them.
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So contributions to help decrease the distro-dependencies are welcome.
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Currently dracut lives on github.com and kernel.org.
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The tarballs can be found here:
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http://www.kernel.org/pub/linux/utils/boot/dracut/
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ftp://ftp.kernel.org/pub/linux/utils/boot/dracut/
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Git:
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git://git.kernel.org/pub/scm/boot/dracut/dracut.git
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http://git.kernel.org/pub/scm/boot/dracut/dracut.git
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https://git.kernel.org/pub/scm/boot/dracut/dracut.git
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git@github.com:dracutdevs/dracut.git
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Git Web:
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https://github.com/dracutdevs/dracut.git
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http://git.kernel.org/?p=boot/dracut/dracut.git
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Project Documentation:
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http://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html
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Project Wiki:
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http://dracut.wiki.kernel.org
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See the TODO file for things which still need to be done and HACKING for
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some instructions on how to get started. There is also a mailing list
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that is being used for the discussion -- initramfs@vger.kernel.org.
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It is a typical vger list, send mail to majordomo@vger.kernel.org with body
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of 'subscribe initramfs email@host.com'
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Licensed under the GPLv2
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