Upgrade to Ubuntu 20.04 from 19.10
Usually I upgrade from one partition to another using a semi-manual process. This time that didn't work (the ISO didn't load) so I tried the automatic upgrade process using do-release-upgrade.
There was a major issue with this upgrade, with loading my root filesystem. The error message was:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
To make this work I needed to load the previous kernel in safe mode, fix up the packages (which I think rebuilds the kernel init image?) and then reboot in the new kernel. This was explained in this Ask Ubuntu answer from krangerich.
- Hold SHIFT during boot to get GRUB menu (it will appear after the first failed boot automatically, though)
- Choose "Advanced options for Ubuntu"
- Choose the older kernel in recovery mode (Linux 5.3.0-51-generic (recovery mode))
- In the Recovery Menu, choose "dpkg - Repair broken packages"
- After repair, reboot. Hold SHIFT again
- Now choose "Advanced options for Ubuntu"/older Kernel again, this time WITHOUT recovery mode
- System should now properly boot with GUI. uname -a will show the old kernel 5.3.0
- Simply reboot again
- System should now magically boot with GUI and the new 5.4.0 Kernel