While the resolution was found in the Fedora forums as RedHat is built from successfull pilots of new code in Fedora in may exist in RedHat systems as well.
I had major issues upgrading my KVM F29 instances to F30. Every attempt attempt resulted in the “grub>” prompt. The beauty of KVM instances of course is I could just restore the qcow2 disk image and retry a lot of different options until I found the post with the solution to the issue.
This does affect physical machines as well, the post I found with the resloution was posted by someone who had hit the issue with a physical system and had to resort to live-cd to rebuild their grub setup. I was lucky in that the only physical machine I had updated was recently rebuilt from F28 and uograded to F29 before I did the F30 upgrade, so was up-to-date enough to upgrade OK, if I had attempted the upgrade on my main machine it would have been bricked, well at the “grub>” prompt requiring hours of work with a live-cd to recover.
I am dubious about taking the risk of updating the F29 OS on my dual boot laptop as there are lots of posts reporting that grub2 can only find windoze partitions after an upgrade to F30, but I guess I will have to attempt it at some point. That is probably a seperate issue I may post on if that goes wrong.
Anyway the issue identified by the post I found is that on BIOS machines (and KVM as it emulates a BIOS environment) I have been running a while that have been upgraded through F24,F25,F26,F27,F28,F29 and now F30 the updates will update the grub2 software packages installed but do not actually update the physical grub2 boot environment; the MBR (or boot sector if you boot off a partition instead of the MBR) itself is not updated with the newer versions of the software; the boot sector becomes stale.
With the update to F30 the differences between the stale entries in the MBR and the installed software on the system(s) result in the “grub>” prompt being displayed instead of the boot menu. Somewhere along the upgrade chain the way grub2 is layed out on the filesystem has changed and the older MBR version of grub2 cannot handle the new layout.
The way to sucessfully update the KVM instances is to replace the normal upgrade of
sudo dnf upgrade --refresh sudo dnf install dnf-plugin-system-upgrade sudo dnf system-upgrade download --releasever=30 sudo dnf system-upgrade reboot
With the below, there is just the one extra command
sudo dnf upgrade --refresh sudo dnf install dnf-plugin-system-upgrade sudo dnf system-upgrade download --releasever=30 sudo grub2-install /dev/vda # < ---- the extra line, change to your boot disk MBR or partition sudo dnf system-upgrade reboot
Obviously on physical hardware you need to know if you are booting from the MBR or a partition on a disk, and perform the grub2-install onto the correct boot device; and also it is only needed if you also have not done so for a while, personally I will do it for every new upgrade.
Fedora 30 grub issues after the upgrade are getting quite a few posts raised on the furums, this must be one of the messiest upgrades in quite a while. Not looking forward to upgrading the dual boot laptop at all.
