Software⏱️ 3 min read📅 2026-06-11

How to Fix: Dual booting Windows 8 and Ubuntu 12.04 with EFI. Got "error: unknown filesystem" and grub rescue prompt

Error fixing dual booting issue with Windows 8 and Ubuntu 12.04.

Quick Answer: Try booting in safe mode or using a different GRUB rescue command, such as `grub rescue>set timeout=10` to wait for 10 seconds before continuing.

📋 Table of Contents

  1. 💡 Why You Are Getting This Error
  2. 🛠️ Step-by-Step Verified Fixes
  3. 💡 Conclusion

The error 'unknown filesystem' and Grub rescue prompt can be frustrating for users who have dual-booted Windows 8 and Ubuntu 12.04 with EFI on their Toshiba Satellite S855-S5381 laptops. This issue typically occurs when the hibernate feature of Windows 8 has hijacked the HDD, causing GRUB to drop to rescue mode.

In this guide, we will walk you through a step-by-step process to resolve the issue and get your system up and running again.

💡 Why You Are Getting This Error

  • The primary reason for this error is that Windows 8's hibernate feature has taken over the HDD, causing GRUB to lose access to the filesystem. This can happen when the user accidentally enables fastboot mode while installing Ubuntu.
  • An alternative reason could be a misconfigured bootloader or a corrupted EFI system table.

🛠️ Step-by-Step Verified Fixes

Rebooting and Rescuing from Grub

  1. Step 1: Restart your laptop and immediately press the key to enter the BIOS settings (usually F2, F12, or Del). Enter the BIOS settings and set the boot order to prioritize the USB drive containing the live Ubuntu environment.
  2. Step 2: Save the changes and exit the BIOS settings. The live Ubuntu environment should now load and display a GRUB menu. Select the 'Boot from USB' option and let the system boot into the live environment.
  3. Step 3: Once in the live environment, open a terminal and run the command `sudo grub-install --removable /dev/sda` (assuming the HDD is mounted on /dev/sda). This will reinstall the GRUB bootloader on the EFI partition.

Boot-Repair with Advanced Settings

  1. Step 1: Create a bootable USB drive containing the Boot-Repair tool and the recommended settings. You can download the ISO file from the official website and create a bootable USB drive using a tool like Rufus or Etcher.
  2. Step 2: Insert the USB drive into your laptop and restart it. Enter the BIOS settings and set the boot order to prioritize the USB drive containing the Boot-Repair environment. Save the changes and exit the BIOS settings.

💡 Conclusion

After following these steps, you should be able to resolve the 'unknown filesystem' error and get your system up and running again. If you are still experiencing issues, it may be necessary to perform a clean installation of Ubuntu or seek further assistance from a Linux expert.

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