Ubuntu upgrade from 18.04 to 20.04 hangs

After many many failed attempts, I was finally able to troubleshoot this issue so that I can access my droplet normally again. The upgrade to 20.04 seems to be successful, and remaining errors are resolved (as far as I can tell).

The solution centered around recovering the grub build, which fixes the kernel panic. I was unable to do this without first addressing several other errors (see below), but here are the steps recommended by support:

1. First, boot your droplet into the Recovery ISO then access the Droplet using the console via your Cloud Panel login, or you may access the Recovery ISO via SSH by connecting to your Droplet’s IP while it’s booted into the Recovery ISO.

2) Once connected to the recovery environment, use option #6 at the Recovery menu to be placed at a root BASH shell where the remaining steps can be performed.

3. Mount your Droplet’s disk by issuing the below commands, one at a time:

mount /dev/vda1 /mnt

mount --bind /dev /mnt/dev

mount --bind /dev/pts /mnt/dev/pts

mount --bind /proc /mnt/proc

mount --bind /sys /mnt/sys

4. Attempt to chroot into the filesystem that you’ve just mounted:

chroot /mnt/

5. Reinstall the GRUB bootloader:

grub-install /dev/vda

update-grub

6. Navigate back to the Cloud panel and switch the Droplet back to booting from its own Hard Disk, then power the Droplet off/on.

Again, these steps did work in the end, but before I could follow them successfully, I first had to troubleshoot these errors:

E: dpkg was interrupted

This one is simple to resolve by using the command suggested in the error: sudo dpkg --configure -a. This error must be resolved before the next one can be.

grub-install: error: /usr/lib/grub/i386-pc/modinfo.sh doesn't exist.   Please specify --target or --directory.

I was able to resolve this with sudo apt-get install grub-pc.

Temporary failure resolving 'mirrors.digitalocean.com'

This was part of a series of errors and warnings I got after correcting the dpkg error and trying to run grub-install. This seemed to be related to nameservers on /etc/resolv.conf, and though I don’t know why, this seemed to solve it both times I tried:

1. From the recovery menu, use options 1 and 5 in the recovery menu to mount the disk image and chroot in.
2. Open the resolv.conf file with vi /etc/resolv.conf and close without saving. (Maybe someone else can explain why this worked?)
3. Exit back out to recovery menu and use option #6 to continue with grub recovery steps.