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Revision as of 14:53, 13 March 2014

Modular Kernel Packaging for Cloud


Kernel modules that are not necessary in virtualized environments become optionally (un)installable.


  • Name: Cloud SIG / Sandro Mathys
  • Email:
  • Name: Kernel Team / Josh Boyer
  • Email:
  • Product: All Cloud products
  • Responsible WG: Cloud

Current status

  • Targeted release: Fedora 21
  • Last updated: 2014-03-13
  • Tracker bug: <will be assigned by the Wrangler>

Detailed Description

Space is precious in the cloud, therefore the Cloud SIG tries to keep the images' footprint as small as reasonably possible. Therefore, we'd like to split the kernel into two (plus one meta) packages. One package would contain the core modules, i.e. a minimum(-ish) set of drivers to only just be able to run in virtualized environments. And another package for the rest. The 'kernel' package would then become a meta package that installs both (-core and -drivers).

Benefit to Fedora

  • Possibility to install Fedora with a smaller footprint.
  • Official Fedora cloud images will become smaller.


Normal installations will continue installing the kernel (meta-)package and users should not notice any difference. Same goes for updating from earlier Fedora releases. But where desired, it should become possible to install only a reasonably minimal subset of kernel modules.

  • Proposal owners:

The kernel package needs to be changed to produce a meta- (kernel) and two new packages (-core and -drivers) packages additionally to those already built out of the SRPM. Aside from the obvious changes to the package spec file, that includes evaluating what modules need to go into which package and making sure updating from pre-split kernel packages works as expected. Most of this work has already been done but still requires some fine-tuning:

  • Other developers:
    • anaconda: Must allow to install kernel-core instead of kernel, when using a kickstart file
    • yum: Must treat kernel-core like core (install instead of update). Note that if kernel is installed, so is kernel-core but not necessarily vice-versa. Also, installing kernel and kernel-drivers if kernel-core has already been installed should work as expected (i.e. they should be counted as one kernel not two or three). So should removing 1) only kernel and kernel-drivers (leaving kernel-core) and 2) removing all three packages.
    • dnf: like yum
    • possibly others that are affected by the split must adapt accordingly
  • Release engineering: No changes necessary.
  • Policies and guidelines: No changes necessary.

Upgrade/compatibility impact

Full compatibility and upgrade-support. No noticeable impact. Systems with pre-split kernel packages will install the new kernel meta-package which in turn will install kernel-core and kernel-driver. All three together are equal to the pre-split kernel package.

How To Test

  • Updating from F20 to F21 (or any pre-split kernel to any post-split kernel) should work as expected, i.e. kernel, kernel-core and kernel-drivers should be installed and be booted by default.
  • In virtualized environments (including clouds) only installing kernel-core but no kernel and kernel-drivers should suffice to work as expected.
  • If only kernel-core but not kernel is installed, yum (and dnf) should install updates instead of updating the package. The same should still be true for the kernel package, if installed.
  • The kernel should work as expected, i.e. the usual kernel tests should be performed.
  • It must be possible to remove kernel and kernel-drivers (and leaving only kernel-core).
  • It must be possible to install kernel and kernel-driver (if only kernel-core was installed).
  • Anaconda should somehow allow to install only kernel-core instead of kernel, through kickstart.
  • Make sure whatever you expect from your kernel that worked before, still works.

User Experience

Two more packages will be installed (visible in yum/dnf and rpm), but no noticeable change otherwise.


See Scope, above.

Contingency Plan

  • Contingency mechanism:
    • The kernel-split could be reverted, if really necessary. But as this work is nearly finished and the standard use cases are not impacted, it's unlikely we'll need to take this step. Either way, this shouldn't matter to any other packages.
    • If support in anaconda for kernel-core is not ready in time, it should ship without it.
    • If support in yum/dnf for kernel-core is not ready in time, it should ship without it. Also, no product should then be shipped without kernel/kernel-drivers and removing these packages should be advised against.
  • Contingency deadline: We really want this in F21 Alpha already to allow for a full QA cycle of kernel, anaconda and yum/dnf, i.e. would revert before the change deadline if we can't meet the target.
  • Blocks release? No.
  • Blocks product? No.


N/A (not a System Wide Change)

Release Notes