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ktest setup: GRUB submenu fixes #486

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Mar 28, 2024
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ktest setup: GRUB submenu fixes #486

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22 changes: 15 additions & 7 deletions getting_started/setup_linux/setup_ktest_environment.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -58,16 +58,24 @@ Set up a target
sudo emacs /etc/default/grub

b) Change ``GRUB_DEFAULT=[n]`` to ``GRUB_DEFAULT=saved``.

c) Add ``GRUB_DISABLE_SUBMENU=y`` to the end of the file and save it.

This step is necessary because submenus confuse ktest.
c) You must disable GRUB submenus because they confuse ktest:

.. code-block:: console

echo 'GRUB_DISABLE_SUBMENU=y' | sudo tee -a /etc/default/grub.d/disable-submenu.cfg
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the commit is saying that GRUB_DISABLE_SUBMENU=true is the documented setting and not with y?

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  • The documentation changed from y (unusual) to true (common)
  • The _implementation changed from: "y only" to: "y OR true".

=> To be compatible with ALL grub versions, stick to y.


d) Update the grub configuration.

.. code-block:: console

sudo update-grub

# Better safe than _very_ sorry
sudo cp /boot/grub/grub.cfg /boot/grub/saved_grub.cfg

sudo update-grub
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Note: this sometimes can cause un-bootable system which can be only recovered by booting to a live env, chrooting to the existing linux install and grub-install --target=x86_64-efi ....

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@marc-hb marc-hb Feb 29, 2024 •
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I tried to chroot and run update-grub inside the chroot but that did not work, it failed with: can't find device for /, is /dev mounted?
GRUB was still installed fine on my system in that instance, that wasn't my problem.

What worked for me was to find and manually enter grub commands and parameters at boot time. This let me boot. Then I disabled the submenus and ran update-grub from the "real" system.

Different OS and different situations will require different solutions. Rescuing unbootable systems is a very complex topic; we can't provide bullet proof advice in such a limited space here.

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I tried to chroot and run update-grub inside the chroot but that did not work, it failed with: can't find device for /, is /dev mounted? GRUB was still installed fine on my system in that instance, that wasn't my problem.

Few things should be done to be able to update grub in chroot, something like:
https://wiki.gentoo.org/wiki/Chroot#Configuration

What worked for me was to find and manually enter grub commands and parameters at boot time.

Wow

This let me boot. Then I disabled the submenus and ran update-grub from the "real" system.

Different OS and different situations will require different solutions. Rescuing unbootable systems is a very complex topic; we can't provide bullet proof advice in such a limited space here.

Sure!

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@marc-hb Are you ready for this PR to be merged? Thanks.

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Yes please merge.

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@marc-hb Thanks!


# Make sure submenus are actually disabled
grep submenu /boot/grub/grub.cfg

#. Set the default kernel.

Expand All @@ -84,7 +92,7 @@ Set up a target
# Print your currently booted (and known-safe) option
cat /proc/cmdline
# List the grub entries
awk '/^menuentry/ { print i++, '\t', $0 }' /boot/grub/grub.cfg
awk '/^menuentry|submenu/ { print i++, '\t', $0 }' /boot/grub/grub.cfg
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there should not be any submenu at this point?

But sudo might be needed to actually read the grub.cfg

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there should not be any submenu at this point?

Not in theory.

In practice this "magic" command is typically re-used across devices - including devices that still have submenus for whatever reason. And the consequences can be deadly.

But sudo might be needed to actually read the grub.cfg

In my experience it's not; I use this command all the time.

# Find the entry that matches the output of the
# first command you ran, and take note of its number
sudo grub-set-default [n] # Where [n] is that number
Expand Down Expand Up @@ -135,7 +143,7 @@ Set up a target
#=> saved_entry=6

# Show all, numbered kernel choices without (re)booting
awk '/^menuentry/ { print i++, '\t', $0 }' /boot/grub/grub.cfg
awk '/^menuentry|submenu/ { print i++, '\t', $0 }' /boot/grub/grub.cfg
#=> 5 menuentry ...
#=> 6 menuentry 'Ubuntu, with Linux 5.4.0-53-generic' --class ubuntu ...
#=> 7 menuentry ...
Expand Down
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