This post is primarily a personal reference for fixing a bootloader issue I encountered on my grandfather's computer. I'm incredibly proud that he's embraced Linux Mint, so I wanted to document how I fixed it in case I need to do this again or help others facing the same issue.
The Boot Error Explained
During startup, the system briefly displayed the error Failed to Open \efi\ubuntu\ before continuing to boot.
While the system functioned despite this error, the message indicates a conflict between the UEFI Secure Boot shim and the specific GRUB version on older hardware.
The Fix
Open Terminal
Log in to Linux Mint. Open a terminal window using Ctrl + Alt + T or search for "Terminal" in the application menu.
Verify Your Drive
Most older systems use /dev/sda. If you're unsure, run:
lsblkYour main drive will be listed at the top. If it's not /dev/sda, use the correct identifier in the next step.
Reinstall GRUB
Run the installation command using your drive identifier from Step 2. The --no-uefi-secure-boot flag bypasses the signature requirement:
sudo grub-install --no-uefi-secure-boot /dev/sdaReplace /dev/sda if your drive identifier is different.
Update Configuration
Finally, regenerate the GRUB configuration file to ensure all operating systems are detected and the new settings are applied:
sudo update-grubReboot your computer. The \efi\ubuntu\ error should be gone.
Technical Background
UEFI Secure Boot verifies the bootloader's digital signature before execution. On older systems, the firmware implementation is often strict or outdated, rejecting the generic signed "shim" that Ubuntu/Mint uses. Reinstalling GRUB with the --no-uefi-secure-boot flag tells the system to skip this check and use a configuration compatible with the hardware.
Linux is for everyone, even grandfathers.
Seeing him use Linux confidently is what makes this troubleshooting worthwhile.