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Fix dual boot that lost Windows

We'll confirm Windows is missing from GRUB, run os-prober, enable it in GRUB config, and run update-grub—or tell you when to escalate.

Troubleshooting · Servers & Linux
15–30 min
What you'll need
  • Root or sudo access in Linux
Step 1 of 5

Quick triage — pick your path

Quick triage — pick your path

Choose the option that matches what you see. You can jump straight to that section.

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Steps

Goal: Confirm Windows is missing from GRUB, run os-prober, enable it in GRUB config, and run update-grub.

  • Power on and check the GRUB menu. Note whether a Windows entry is listed.
  • Good: GRUB appears but Windows is missing. Proceed to Run os-prober.
  • Bad: GRUB does not appear—see fix-grub-will-not-boot.

Run os-prober

Goal: Detect Windows so GRUB can add it to the menu.

  • Boot into Linux. Run sudo os-prober. Check the output for a line like “/dev/sda1:Windows 10:…”.
  • If os-prober finds nothing, check /etc/default/grub. Set GRUB_DISABLE_OS_PROBER=false (or remove the line if it disables os-prober).
  • Run sudo update-grub. Reboot. Confirm the Windows entry appears in the GRUB menu.

When to get help

Escalate if:

  • os-prober finds nothing and you have confirmed the Windows partition exists.
  • Windows appears in GRUB but will not boot.
  • Secure Boot or UEFI settings block Windows.

Provide: disk layout (lsblk), os-prober output, and steps tried.

Verification

  • The Windows entry appears in the GRUB menu.
  • Selecting Windows boots the system into Windows.
  • You can switch between Linux and Windows by rebooting and selecting the desired entry.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Run os-prober sudo os-prober to detect Windows.
  2. Enable os-prober Set GRUB_DISABLE_OS_PROBER=false in /etc/default/grub.
  3. Run update-grub sudo update-grub to add Windows to the menu.
  4. Escalate Provide disk layout, GRUB config, os-prober output.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Output of lsblk or fdisk -l
  • Output of os-prober
  • Contents of /etc/default/grub
  • Steps already tried

Does GRUB appear but Windows is missing?

GRUB shows only Linux. Windows was there before or you expect it.

Power on and check the GRUB menu. Windows missing: run os-prober and update-grub. GRUB missing: see fix-grub-will-not-boot. Windows present: try booting it—if it fails, different problem.

Yes No

You can change your answer later.

Does os-prober find Windows?

os-prober scans for other OS. It must be enabled in /etc/default/grub.

Run `sudo os-prober`. Finds Windows: run update-grub, reboot. Finds nothing: check GRUB_DISABLE_OS_PROBER, mount Windows partition, check Secure Boot. See Run os-prober.

Yes No

You can change your answer later.

Run update-grub

Run `sudo update-grub`. Reboot. Windows should appear in the menu.

Done

Enable os-prober and retry

Edit /etc/default/grub. Set GRUB_DISABLE_OS_PROBER=false. Run update-grub. If still nothing, check Secure Boot and disk layout.

Done

Escalate

If os-prober finds nothing and Windows partition exists, or Windows appears but will not boot. Provide disk layout and os-prober output.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would Windows disappear from the dual boot menu?
GRUB was reinstalled or updated without os-prober, or os-prober did not run. The Windows partition may be on a different disk. Secure Boot can also hide Windows. Run os-prober and update-grub.
Can I fix dual boot without reinstalling?
Yes. Boot into Linux, run os-prober and update-grub. GRUB will add the Windows entry. No need to reinstall Windows or Linux.
When should I escalate a dual boot issue?
If os-prober finds nothing and you have confirmed the Windows partition exists, or Windows appears in GRUB but will not boot. Provide disk layout and GRUB config.

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