Software⏱️ 4 min read📅 2026-06-15

How to Fix Error 21 Error – Help with Grub Error 21?

Error 21 occurs when GRUB fails to load properly. Removing the offending drive or formatting the Linux partition may resolve the issue.

Quick Answer: Try removing the Ubuntu installation drive or reformatting the Linux partition to bypass GRUB and boot into Vista.

📋 Table of Contents

  1. ⚠️ Common Causes
  2. 🔧 Proven Troubleshooting Steps
  3. ✨ Wrapping Up

The GRUB Error 21 is an issue that affects users who have installed Ubuntu on top of a RAID 0 configuration, specifically with Windows Vista or Windows 7 as the primary operating system. This error occurs when GRUB fails to load properly and gets stuck between the BIOS and the Windows Bootloader. The user has reported that the Windows Vista repair CD finds no problem with their Vista partition, indicating that the issue lies with the GRUB installation.

The frustration of encountering GRUB Error 21 can be overwhelming, especially for users who are new to Linux or have never encountered this specific error before. However, by following the steps outlined in this guide, you should be able to resolve the issue and boot into your Windows Vista partition.

⚠️ Common Causes

  • The primary reason for GRUB Error 21 is that the RAID 0 configuration is not properly recognized by the Linux installation process. When Ubuntu is installed on a RAID 0 setup, it may not be able to detect the individual drives and install GRUB correctly. This can lead to an error message like Error 21, which indicates that GRUB is unable to load stage 1.5.
  • An alternative reason for GRUB Error 21 could be that the Linux partition is not properly formatted or is corrupted in some way. In this case, the issue may be with the file system rather than the RAID configuration.

🔧 Proven Troubleshooting Steps

Remove the offending drive and boot into Vista

  1. Step 1: Disconnect the drive that contains the Ubuntu installation (the 130GB partition). This will allow you to boot into your Windows Vista partition using the Windows Vista repair CD.
  2. Step 2: Insert the Windows Vista repair CD and restart your computer. The repair CD should automatically detect the Windows Vista partition and load the necessary files to boot into the operating system.

Format the Linux partition

  1. Step 1: If you determine that the issue is with the file system, you can try formatting the Linux partition. Use a tool like `sudo mkfs.ext4 /dev/sdb1` (assuming the 130GB partition is on drive sdb) to format the partition with an ext4 file system.
  2. Step 2: Once the partition is formatted, you may need to reinstall GRUB or use a different boot loader. The exact steps will depend on your specific Linux distribution and configuration.

✨ Wrapping Up

In summary, GRUB Error 21 can be resolved by removing the offending drive and booting into Windows Vista using the repair CD. If you are unable to remove the drive, you can try identifying which drive GRUB was installed on and formatting the Linux partition. By following these steps, you should be able to resolve the issue and enjoy a stable and functional Ubuntu installation.

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