Recently I had a Debian Linux VM that wasn’t booting. It was getting a GRUB error: ‘
error symbol grub_register_command_lockdown not found’. Attempting to select any other boot option, including the listed recovery options, all took me back to this same error.
I didn’t find a lot of helpful information while searching for that error. In the end, the solution was to re-install GRUB. These steps walk through how I was able to re-install GRUB in a Debian Linux VM on DigitalOcean (DO).