Features/DracutHostOnly

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Contents

Dracut HostOnly

Summary

Only create "host-only" initramfs images. A generic fallback image will be generated, if it does not exist and never ever be removed.

Owner

Current status

  • Targeted release: Fedora 19
  • Last updated: 2013-05-16
  • Percentage of completion: 100%

Detailed Description

Current initramfs images contain most of the kernel drivers to boot from any hardware. This results in a very big initramfs, which takes a long time to load on system start and a long time to create on kernel updates. Switching to host-only will improve the situation. To cope with hardware change, a boot entry "Rescue System" should be installed with a full fledged initramfs also containing debug tools. This boot entry can then be used to recover from hardware changes and also from unforseen software failure after updates.

Benefit to Fedora

Less /boot usage. Faster boot and updates. Full fledged rescue mode available.

Scope

  • [ DONE ] dracut is already capable of producing host-only initramfs images, as well as rescue images
  • [ DONE ] dracut has to source config files from "/usr/lib/dracut/dracut.conf.d", although the same filenames in "/etc/dracut/dracut.conf.d" will have priority
  • [ DONE ] dracut has to be changed to create the rescue initramfs image and the rescue boot entry, if it does not yet exist
  • [ DONE ] dracut has to provide the following subpackages: dracut-nohostonly and dracut-norescue
  • [ DONE ] dracut has to implement "dracut --regenerate-all" to regenerate all normal initramfs with the current hardware
  • [ REJECTED ] and call "yumdb set installonly keep kernel-$version" for the kernel, which is used for the rescue image, otherwise kernel modules cannot be loaded in the real root. Reason: the rescue image has enough kernel modules already to mount the root device and /usr, so that the user can call "dracut --regenerate-all".
  • [ REJECTED ] dracut has to ship "/usr/lib/dracut/dracut.conf.d/99-hostonly.conf" with: [[ $hostonly ]] || hostonly="yes" in a "dracut-hostonly" subpackage. Reason: we ship dracut-norescue and dracut-nohostonly packages. The default setting should need no additional subpackage.

How To Test

  • install F19
  • see two boot entries in grub: first one with the current kernel, second one with the rescue entry
  • /boot should contain one big initramfs belonging to the rescue image. The rest of the initramfs images should be way smaller in comparison.
  • every boot entry must be bootable
  • kernel upgrade must not remove the kernel used for the rescue boot entry

User Experience

User should see no difference, besides faster boot and updates. On boot failure, the user now has a "Rescue system" boot entry.

Dependencies

  • dracut
  • grubby-8.23-1.fc19

Contingency Plan

If the feature cannot be completed, we switch back to non-hostonly initramfs images, which is a configure switch in dracut and very easy to do.

Documentation

Release Notes

  • This Fedora release builds an initramfs tailored especially for your computer hardware. If you change your machine or partitions or significant hardware, you might have to boot with the "Rescue" boot entry and execute "dracut --regenerate-all". If you want your initramfs to be hardware independent, install the "dracut-nohostonly" rpm package. If you don't want rescue images at all (like in virtual machines), install the "dracut-norescue" rpm package.

Comments and Discussion