[Bug 1871186] Re: grub-mkconfig prefers /etc/default/grub.d settings

[Benjamin Gemmill]

Right now for cloud images, the flow of editing /etc/default/grub to
modify GRUB_CMDLINE_LINUX_DEFAULT and then running update-grub simply
doesn't work.

It feels like either a warning in /etc/default/grub or having
50-cloudimg-settings.cfg edited to forward existing cmdline arguments
seems like the path of least surprise for that value.

For values that aren't appendable, like the OP's GRUB_TIMEOUT, a comment
pointing the user to /etc/default/grub.d would be really useful.

All /etc/default/grub says to do after editing the file is run update-
grub. When that doesn't work, the user is going to be surprised!

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https://bugs.launchpad.net/bugs/1871186

Title:
  grub-mkconfig prefers /etc/default/grub.d settings

Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  Since the fix for bug 901600 was commited, setting in
  /etc/default/grub now can be overiden by /etc/default/grub.d. It helps
  developers to make customized images, but it can really blows up the
  brain to the rest users.

  I've lost an hour trying to understand why grub ignores my
  GRUB_TIMEOUT settings, until I found hostile file 50-cloudimg-
  settings.cfg, that silently overrides my setting. I think such
  behaviour violates simple principle — user settings must have the
  higest precedence.

  I understand that changing this behaviour, may break a lot of code. So
  please at least add BIG RED BANNER to /etc/default/grub with warning:
  before changing something in the file, check all the files in
  /etc/default/grub.d for conflicting settings, because they have higher
  precedence.

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