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🛠️ GRUB EFI Repair Script

If you run Windows on Dual Boot with Linux, you may have faced issues like your windows partition overwrites the linux boot loader forcing user to log in on windows.

This script was created to solve that issue in UEFI based Linux systems.

A simple Bash script to reinstall GRUB on UEFI-based Linux systems and set the correct boot order.

⚠️ Requirements & Conditions

Before running this script, ensure your system meets all of the following conditions.

1. UEFI System Required

This script works only on UEFI systems. Legacy BIOS systems are not supported.

It uses:

grub-install --target=x86_64-efi

2. EFI Partition Must Be Mounted at /boot/efi

Your system must have an EFI System Partition (ESP) mounted at:

/boot/efi

The script expects this directory to exist:

/boot/efi/EFI

If your distribution uses a different mount point (such as /efi or /boot), adjust the script accordingly.

3. GRUB Must Be Installed and Used

This script only works with GRUB.

It does NOT support:

  • systemd-boot
  • rEFInd
  • LILO
  • vendor-specific boot managers

Running it on these setups will result in errors.

4. update-grub Must Exist

The script uses:

update-grub

This command is available only on Debian-based systems:

  • Debian
  • Ubuntu
  • Linux Mint
  • Kali
  • MX Linux

It will not work on:

  • Fedora / RHEL / CentOS / Rocky / AlmaLinux
  • Arch Linux / Manjaro
  • OpenSUSE

Those use grub2-mkconfig.

5. Bootloader ID Defaults to “Debian”

The GRUB installation uses:

--bootloader-id=Debian

Different distros use different EFI bootloader IDs:

  • Ubuntu → ubuntu
  • Fedora → fedora
  • Linux Mint → LinuxMint
  • Arch Linux → arch

Update this value if needed.

6. Requires efibootmgr Support

The script modifies UEFI boot order using:

efibootmgr -o

This requires:

  • Firmware that allows BootOrder modification
  • Root access

Some cloud/VPS providers restrict this capability.

7. Must Be Run as Root

You must run the script with sudo or as root because it executes privileged commands:

  • grub-install
  • update-grub
  • efibootmgr

8. Multi-Boot Systems

If multiple OSes are installed (e.g., Windows + Linux), this script will set Debian GRUB as the first boot entry, overriding others.

9. Risk Warning

Changing GRUB/EFI settings can make a system unbootable if misconfigured.

Recommended:

  • Keep a bootable USB handy
  • Confirm your EFI mount point
  • Back up important data

📜 Usage

Make the script executable:

chmod +x grub-fix.sh

Run the script:

sudo ./grub-fix.sh

Reboot when done.

✔ What the Script Does

  1. Verifies EFI directory presence
  2. Lists available EFI boot entries
  3. Reinstalls GRUB to the EFI System Partition
  4. Updates GRUB configuration
  5. Detects the Debian boot entry
  6. Sets Debian as the first boot option
  7. Completes cleanly

📌 Notes

This script is designed for Debian-based Linux systems with a standard EFI layout. It is not guaranteed to work on all Linux distributions.