The Kubuntu update , if it updated the kernel, would have included an update-grub command… so that grub would
boot the new kernel.
If Kubuntu does not have os-prober installed, the update-grub would not have detected the other Linux, so it would not appear in the grub menu.
I am assuming that Kubuntu is the Linux that controls grub… ie the one that originally installed grub , and the one that stores the grub config files.
If LM had been the one controlling grub, the kubuntu upgrade would not have altered the grub menu. You would have had to go into LM and do update-grub there, to update the grub menu so it would see the new kubuntu kernel.
So it did not destroy grub, just made a mess of its menu. Because it only found kubuntu, it may have byoassed the menu and just booted… it depends, dpsome distros do that, others always make a grub menu, even if it has only one item in it.
Managing multiboot is not straightforward.
The survival recipe is
- make sure you know which linux controls grub
- if the non grub controlling linux updates a kernel, go to the controlling linux and do
update-grubthere - never do
grub-installfrom the non controlling linux… you will make it the controlling linux. - make sure
os-proberis enabled in the controlling linux
If you follow that managing multiboot is
a breeze