How to Fix Missing GRUB Bootloader on a Dual Boot Computer

Published 2026-10-16 · LuxuriousComputers Repair

You had Linux and Windows dual-booting on the same computer, and now the GRUB menu that lets you choose which operating system to boot has disappeared. The computer boots straight into Windows, or shows an error like no such device, error: unknown filesystem, or simply a blank screen with a grub rescue prompt. GRUB disappears most commonly after a Windows update overwrites the boot record, after changing the BIOS boot order, or after disk operations that modify the EFI partition.

Why GRUB disappears

• Windows update: Major Windows updates (feature updates, not monthly patches) can overwrite the EFI boot entry for GRUB with the Windows Boot Manager entry. Windows does not delete GRUB files — it just changes the default boot entry so the firmware skips GRUB entirely
• BIOS/UEFI boot order changed: The boot order in your BIOS may have been changed (manually or by an update) to prioritize Windows Boot Manager over the Linux/GRUB entry
• Windows reinstall or repair: Reinstalling Windows or running Windows Startup Repair replaces the Master Boot Record (on BIOS/MBR systems) or modifies EFI boot entries, removing GRUB
• Disk operations: Partitioning tools, cloning software, or resizing partitions can modify the partition table in ways that break GRUB's ability to find its configuration files

Check the BIOS boot order first

Before doing anything complex, check if GRUB's boot entry still exists but is just not first in the boot order:

1. Restart and enter the BIOS/UEFI setup (press F2, Del, or the key shown at boot)
2. Go to the Boot tab or Boot Order section
3. Look for entries like ubuntu, Linux, or your Linux distribution name alongside Windows Boot Manager
4. If the Linux entry exists, move it above Windows Boot Manager in the boot order
5. Save and exit. If GRUB appears, the fix was just the boot order — no repair needed

Use the BIOS boot menu

Many computers have a one-time boot menu (usually F12, F8, or Esc at startup). This shows all available boot entries without permanently changing the order. If your Linux entry appears here, select it to boot into GRUB and Linux.

Restore GRUB from a Linux live USB

If the BIOS has no Linux boot entry or GRUB is genuinely broken, restore it using a Linux live USB:

What you need

• A USB drive with a Linux live image (Ubuntu, Linux Mint, or the same distribution you have installed). You can create one using Rufus or Balena Etcher on another computer
• Boot from the USB drive (use the BIOS boot menu to select the USB)

UEFI systems (most modern computers)

1. Boot into the live Linux environment and open a terminal
2. Identify your Linux partition: run lsblk or sudo fdisk -l. Find the partition where Linux is installed (look for an ext4 or btrfs filesystem, typically something like /dev/sda2 or /dev/nvme0n1p2). Also identify the EFI System Partition (ESP), typically a small FAT32 partition around 100 to 500 MB, often /dev/sda1 or /dev/nvme0n1p1
3. Mount the Linux partition: sudo mount /dev/sdXN /mnt (replace sdXN with your actual partition)
4. Mount the EFI partition: sudo mount /dev/sdX1 /mnt/boot/efi (replace with your actual EFI partition)
5. Mount the necessary virtual filesystems: sudo mount --bind /dev /mnt/dev then sudo mount --bind /proc /mnt/proc then sudo mount --bind /sys /mnt/sys
6. Chroot into your Linux installation: sudo chroot /mnt
7. Reinstall GRUB: grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu (replace ubuntu with your distribution name if different)
8. Update GRUB configuration: update-grub — this scans for all operating systems and adds them to the GRUB menu. You should see lines like Found Windows Boot Manager confirming it detected Windows
9. Exit the chroot: exit
10. Unmount everything: sudo umount /mnt/boot/efi then sudo umount /mnt/dev /mnt/proc /mnt/sys then sudo umount /mnt
11. Reboot and remove the USB drive. GRUB should now appear with both Linux and Windows options

Legacy BIOS/MBR systems

1. Boot from the live USB and open a terminal
2. Identify and mount your Linux partition as described above (skip the EFI partition step)
3. Mount virtual filesystems and chroot as described above
4. Reinstall GRUB to the disk: grub-install /dev/sda (use the disk, not a partition — sda not sda1)
5. Update GRUB: update-grub
6. Exit, unmount, and reboot

Boot-Repair tool

If the manual process seems complex, the Boot-Repair tool automates GRUB restoration:

1. Boot from an Ubuntu live USB
2. Open a terminal and run: sudo add-apt-repository ppa:yannubuntu/boot-repair then sudo apt update then sudo apt install boot-repair
3. Run boot-repair and click Recommended Repair
4. Boot-Repair detects the installed systems, reinstalls GRUB, and configures it to show all available operating systems

GRUB rescue prompt

If you see grub rescue instead of a normal boot, GRUB is partially present but cannot find its configuration files:

1. At the grub rescue prompt, list available partitions: ls — this shows partitions like (hd0,msdos1), (hd0,gpt2), etc.
2. Find which partition has your Linux installation: try ls (hd0,gpt2)/ or ls (hd0,msdos2)/ for each partition until you find one that lists Linux directories (bin, boot, etc, home, usr)
3. Once found, set the root: set root=(hd0,gptN) and set prefix=(hd0,gptN)/boot/grub (replace N with your partition number)
4. Load the normal module: insmod normal then normal
5. GRUB should now show its menu. Boot into Linux and run sudo update-grub followed by sudo grub-install to make the fix permanent

Prevent GRUB from disappearing again

• After Windows updates: Major Windows updates may overwrite the boot entry again. Keep your Linux live USB handy for quick restoration. Alternatively, install the rEFInd boot manager — it is more resilient to Windows boot entry changes because it scans for bootable entries dynamically rather than relying on a fixed EFI boot variable
• BIOS boot order: Some BIOS implementations reset the boot order after battery removal or BIOS updates. Check the boot order if GRUB suddenly disappears without any software changes
• Separate EFI entries: In UEFI mode, use efibootmgr (from Linux) to verify that both the Linux and Windows boot entries exist and that Linux is first: efibootmgr -v shows all entries with their order

Windows-only boot after Linux deletion

If you deleted the Linux partitions but GRUB is still trying to load (and failing because the files are gone), you need to remove GRUB and restore the Windows bootloader:

1. Boot from Windows installation media
2. Select Repair your computer, Troubleshoot, Command Prompt
3. Run: bootrec /fixmbr (for MBR systems) or use bcdboot C:\Windows /s S: (for UEFI, where S: is the EFI partition)
4. Restart. Windows should boot normally without GRUB

Dual boot repair in Columbus or Delaware

If your dual boot GRUB menu has disappeared and the restoration steps above did not work or seem too complex, LuxuriousComputers can restore GRUB, fix the boot order, verify both operating systems boot correctly, and configure the bootloader to survive future Windows updates.