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

Verified 2 min read

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

Tested onPro (26H2) · Build 26300.9457 · x64
E1
Build
26300.9457
Edition
Pro (26H2)
Architecture
x64
Support
Documentation (E1)
Evidence
E1Official documentation
Verified
2026-10-28
Page type
Task

The short answer

Section titled “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

Section titled “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

Section titled “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

Section titled “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

Section titled “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

Section titled “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

Section titled “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.

Sources