boot an alternate kernel

[Aaron Rainbolt]

On Fri, May 27, 2022 at 12:42 AM Bob <ubuntu-qygzanxc at listemail.net> wrote:
>
> ** Reply to message from Aaron Rainbolt <arraybolt3 at gmail.com> on Thu, 26 May
> 2022 21:35:39 -0500
>
> > > SDA1 is the bios-grub partition.
> >
> > Well, in that instance, maybe GRUB is finding the boot menu from your
> > test partition, not the one from your main partition. Try mounting
> > SDA2 and try the commands I mentioned (though do be aware that you
> > might be unable to boot from the test partition if you do this).
>
> The man page for the update-grub command states it runs "grub-mkconfig -o
> /boot/grub/grub.cfg".
>
> If I look at /boot/grub/grub.cfg I see markup language for the boot menu.  The
> menu ior each partition has the menu items for all bootable Ubuntu partitions
> but they are in a different order.  Now that I fixed the problem I can no
> longer tell why the update-grub for SDA9 did not work.  Did it fail to create
> the menu in /boot/grub/grun.cfg or did it fail to copy the menu into grub?  My
> guess is that grub-mkconfig updates the menu for the partition it is booted
> from and that it or someother program copies the menu into grub.  I think it
> should not make any difference which system is booted when the update is done.
> I will have to monitor the updates more closely and check the boot menu
> whenever it gets updated to determine what is actually happening.

GRUB loads the boot menu from the grub.cfg file, but the thing is, it
only loads one grub.cfg file. So if you have two, and you're updating
one and GRUB is loading the other, then the updated boot menu won't be
displayed. GRUB was probably finding the test partition's grub.cfg,
and you were updating SDA9's grub.cfg.