How to handle grub on multi-boot systems?

[Bo Berglund]

On Wed, 20 Oct 2021 10:12:29 +0200, Bo Berglund <bo.berglund at gmail.com> wrote:

>QUESTIONS:
>----------
>1) How do I make the extraneous grub entry go away from the boot menu?
>
>2) And how can I set which operating system is the default and listed on top?
>
>3) How do I make the grub managed by one Ubuntu and not all of them?
>
>I tried googling as usual but got to widely varying suggestions...

I made a better google attempt and found this HOWTO:

https://www.howtogeek.com/196655/how-to-configure-the-grub2-boot-loaders-settings/

So I did as it suggested and issued
sudo update-grub
and it fixed the boot menu like I want it.

But I have a different question now:

It seems like the update-grub command uses the /etc/default/grub file located on
my Ubuntu 20.04..

What happens then if I am inside the Ubuntu 18.04 and it triggers the
update-grub command for instance as part of an upgrade like:
sudo apt full-upgrade

The edited /etc/default/grub on Ubuntu 20.04 is then not available so the grub
menu might change unexpectedly...


-- 
Bo Berglund
Developer in Sweden