Grub Bootloader

Grub is the bootloader used on Ubuntu.

Troubleshooting

grub_file_filters not found

After upgrading Ubuntu from Bionic to Focal (20.04), I received the error symbol 'grub_file_filters' not found.

To solve this, I adjusted the boot drive order in the BIOS settings to boot from the /boot partition, as per this StackOverflow solution. Others have suggested running update-grub using a live CD, but the boot drive order seems to be an easier thing to try first.