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WITH WINDOWS 11

Dual-Boot Guide: Installing Ubuntu Alongside Windows 11

Goal: keep Windows 11 (and its boot manager) intact, and add Ubuntu so you can choose either OS at boot.

The two things that bite people most are BitLocker and Fast Startup, so don't skip those steps.

Phase 1 — Back up and prep (in Windows)

  1. Back up your important files. Repartitioning is generally safe, but a power loss mid-resize can corrupt the disk. Don't skip this.

  2. Suspend/disable BitLocker drive encryption. Windows 11 often has this on by default. If Ubuntu's installer shrinks an encrypted partition, you can lock yourself out.

  3. Search "Manage BitLocker" → if your drive shows "On," click Turn off BitLocker (full decrypt — safest), or at minimum Suspend.

  4. Also note your BitLocker recovery key (saved to your Microsoft account at account.microsoft.com/devices/recoverykey) in case the firmware later prompts for it after boot-order changes.

  5. Disable Fast Startup. This leaves the Windows filesystem in a hibernated/locked state that breaks the shared boot partition and can corrupt the NTFS partition from Linux.

  6. Control Panel → Power Options → "Choose what the power buttons do" → "Change settings currently unavailable" → uncheck Turn on fast startup → Save.

  7. Free up space for Ubuntu (you can also do this from the Ubuntu installer, but doing it in Windows is cleaner).

  8. Right-click Start → Disk Management → right-click your Windows (C:) partition → Shrink Volume.
  9. Give Ubuntu at least 30 GB; 60–100+ GB is comfortable if you'll use it regularly. Leave the freed space unallocated — don't format it.

Phase 2 — Make the Ubuntu USB installer

  1. Download the Ubuntu 24.04 LTS ISO from ubuntu.com/download/desktop.
  2. Flash it to an 8 GB+ USB stick with Rufus (rufus.ie) on Windows — select the ISO, keep the default GPT / UEFI scheme, and write it.

Phase 3 — Firmware (BIOS/UEFI) settings

  1. Reboot into firmware setup (usually F2, F10, Del, or Esc at power-on — varies by maker).
  2. Confirm/set:
  3. UEFI mode (not Legacy/CSM) — Windows 11 already requires this.
  4. Secure Boot: leave it ON. Ubuntu supports it fine; no need to disable.
  5. You generally do not need to disable Secure Boot unless you'll install proprietary/third-party kernel drivers that won't sign.
  6. Set the USB as the first boot device (or use the one-time boot menu, often F12).

Phase 4 — Install Ubuntu

  1. Boot the USB → choose Try or Install Ubuntu. You can pick "Try Ubuntu" first to confirm Wi-Fi/trackpad work.

  2. When you reach Installation type, the key screen:

    • If Ubuntu detected Windows, it offers "Install Ubuntu alongside Windows Boot Manager." This is the easiest path — pick it and use the slider to assign space.
    • If that option is missing or you want control, choose "Manual / Something else." Then:
    • Do not touch the existing EFI System Partition (~100–500 MB, FAT32), the Microsoft Reserved partition, the Windows (NTFS) partition, or the recovery partition.
    • In your unallocated space, create one partition: mount point /, type ext4, using all of it. A separate swap partition is optional — modern Ubuntu uses a swap file automatically.
    • For "Device for boot loader installation," select the existing EFI partition (the whole disk, e.g. /dev/sda or /dev/nvme0n1, not a sub-partition). GRUB installs alongside Windows Boot Manager in that EFI partition — it does not erase it.

  3. Finish the install and reboot, removing the USB when prompted.

Phase 5 — After install

  1. On reboot you should see the GRUB menu listing Ubuntu and Windows Boot Manager. Pick either; Ubuntu boots by default after a timeout.

  2. If it boots straight to Windows (some firmware reorders boot entries): go back into firmware setup and move ubuntu above Windows Boot Manager in the boot order. On a few machines you instead select "ubuntu" from the firmware boot menu each time, or set it with efibootmgr from Linux.

  3. Re-enable BitLocker in Windows now if you turned it off and want encryption back.

Key safety notes

  • The single most common failure is Fast Startup or BitLocker left on — handle both in Phase 1.
  • Never let the installer "Erase disk and install Ubuntu" — that wipes Windows. You want alongside or manual.
  • Keep the existing EFI partition; both OSes share it. Install GRUB to the disk, targeting that EFI partition — don't reformat it.