[Bug 1812752] Re: UX: changing GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub has no effect in cloud images

[John Chittum]

I disagree racb -- using the `.d` directory is generally the approach
CPC has used for all configuration. that way users can easily see what
is package maintained and what is changed in the build process. I don't
think the suggestion that CPC change that general guidance because
grub.d is less well known that other `.d` directories is a strong
rationale. It seems fairly "normal" for Ubuntu packages to have
$PACKAGE_CONF.d directories to add additional configuration.

I think mkukri has the correct solution. we should add a comment to the
top level file, and ensure all man pages correctly state how the grub
handles the `.d` directory. And any official Ubuntu docs should be
updated. we can't change the history of everyone that's posted online
about every version of Ubuntu, but changing how we configure things
because information online isn't strictly correct (because it predates
grub.d, posters didn't know about grub.d, etc) doesn't seem like strong
reason.

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https://bugs.launchpad.net/bugs/1812752

Title:
  UX: changing GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub has no
  effect in cloud images

Status in cloud-images:
  New
Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  I need to modify the kernel command line, such as to work around bug
  1573095. I edit GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub and
  rerun update-grub but this has no effect.

  The reason is that this is redefined in
  /etc/default/grub.d/50-cloudimg-settings.cfg and that one overrides
  /etc/default/grub. I was misled by the comment in /etc/default/grub
  and information widely available on the Internet that editing
  /etc/default/grub is sufficient, and looked no further.

  I understand the reason for not modifying /etc/default/grub in cloud
  image builds (to avoid future conffile prompts) and I'm not suggesting
  that it should be modified. To fix this UX issue properly I think the
  grub package needs to provide a mechanism that allows cloud image
  builds to override the default without dropping in an overriding file
  (or for that override file to be the sole place that users need to
  look).

  This affects grub2 2.02-2ubuntu8.9 from Bionic cloud image build
  20190114 for example.

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