# Windows 11 + Linux dual boot: UEFI, partitions, GRUB and BitLocker

> Plan a UEFI dual-boot system with Windows 11 and Linux: free space, shared ESP, Fast Startup, BitLocker, GRUB and recovery.

**Tested on**

- Build: 26300.9457
- Edition: Pro (26H2)
- Architecture: x64
- Evidence: E1
- Verified: 2026-10-28

## The short answer

A reliable dual boot is mostly preparation:

1. **UEFI only.** Both systems must boot in UEFI mode.
2. **Back up and save the BitLocker key.** Repartitioning can trigger recovery.
3. **Shrink Windows from Windows**, not with a Linux tool.
4. **Disable Fast Startup** (and hibernation) before touching the boot order.
5. **Share the existing ESP**; do not create a second ESP on the same disk.
6. **Install Linux after Windows** so GRUB can find Windows.
7. **Test both boots before you need them.**

## Before you start

| Item | Why |
|---|---|
| Full image or file backup | Partitioning and bootloader changes are destructive |
| BitLocker recovery key | Firmware/TPM changes can trigger recovery |
| Windows install USB | Repair the boot manager if GRUB misbehaves |
| Linux USB | The distro’s live environment is your rescue tool |
| Free unallocated space | Shrink C: in Disk Management; leave 50–100GB+ |
| Secure Boot plan | Some distros need MOK enrollment or shim |

## Step 1 — Prepare Windows

1. Update Windows and record the build.
2. Disable **Fast Startup**: `powercfg /h off` (this also removes hibernation).
3. Save the BitLocker key. If you plan firmware changes, suspend BitLocker for one reboot:
   `manage-bde -protectors -disable C: -RebootCount 1`
4. Shrink the Windows partition in **Disk Management**; leave unallocated space. Do not create a Linux filesystem here.
5. Reboot and confirm Windows still boots before installing Linux.

## Step 2 — Install Linux

Boot the Linux USB in UEFI mode, then choose “install alongside” or manual partitioning:

| Partition | Size | Format | Mount |
|---|---|---|---|
| ESP | Existing | FAT32 | `/boot/efi` (do not format if shared) |
| Root | 40–80GB | ext4/btrfs | `/` |
| Home | Remaining | ext4/btrfs | `/home` |
| Swap | Optional | swap/zram | Depends on RAM/hibernation |

Do **not** format the existing ESP. The Linux installer should reuse it. If it insists on creating a new ESP, stop and fix the installer’s boot mode.

## Step 3 — Boot and repair

After install, GRUB should list Windows and Linux. If Windows is missing:

- Boot Windows USB → **Repair your computer** → **Startup Repair**;
- or from Linux, run `update-grub` (Debian/Ubuntu) / `grub-mkconfig -o /boot/grub/grub.cfg`;
- check that the Windows EFI files still exist under `EFI/Microsoft/Boot/`.

If Windows boots but Linux does not, use the Linux live USB and chroot to reinstall GRUB. Keep notes; this is the part people skip.

## BitLocker and Secure Boot

- **BitLocker:** dual boot does not require disabling it permanently, but firmware/boot changes can trigger recovery. Save the key and suspend only for the change window.
- **Secure Boot:** many distros ship a signed shim; others need MOK enrollment. If you disable Secure Boot, Windows 11 still runs, but the machine is no longer in the validated configuration.
- **NTFS access from Linux:** read-only is safer by default. Do not mount a BitLocker volume read-write from Linux without a deliberate tool and backup.

## Recovery plan

- Keep the Windows USB and Linux USB.
- Know how to enter the firmware boot menu.
- Keep a copy of your notes outside the machine.
- Test: boot Windows, boot Linux, then boot Windows again. A dual boot that works once is not verified.

> **Caution: Do not share one /home with Windows**
>
> Use a separate NTFS/exFAT data partition for files both systems need. Do not point Linux `/home` at an NTFS Windows profile.

## Sources

- [Microsoft — UEFI/GPT partitions](https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/configure-uefigpt-based-hard-drive-partitions)
- [Microsoft — BitLocker](https://learn.microsoft.com/en-us/windows/security/operating-system-security/data-protection/bitlocker/)
- [Ubuntu — Install Ubuntu alongside Windows](https://ubuntu.com/tutorials/install-ubuntu-desktop)

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Source: https://windows.homes/en/windows/install/dual-boot/