Installing Windows 11 alongside Linux

Dual boot means running two operating systems on one machine and choosing which one to start at boot. I use it when I want native Linux performance but still need Windows 11 for one app or game. The real work is the disk layout and boot path. Do not rush the partitioning. Back up anything you cannot replace before you touch the disks.

Check whether the machine uses UEFI or legacy BIOS. In Windows 11, press Start, type System Information, open it, and look for “BIOS Mode”. If it says UEFI, plan for an EFI System Partition. If it says Legacy, expect different repair steps. Check whether Fast Startup is enabled too. Open Settings > System > Power & battery > Additional power settings > Choose what the power buttons do > Change settings that are currently unavailable, then clear Turn on fast startup. Fast Startup can leave the Windows partition in a bad state during the Linux install.

Pick the Linux distribution. Ubuntu is a decent beginner choice with broad hardware support. If you want something lighter, choose a lighter distro. For the USB tool, I use Rufus on Windows for UEFI images and balenaEtcher on other platforms. Label the USB so you can find it at boot without guessing.

Setup

You need a few basics before you start:

• A Linux ISO for the distro you picked.
• A USB stick, 4GB or larger.
• At least 20–30GB free on the drive for Linux.
• A full backup of the Windows partition on external storage.

Create the live USB. On Windows with Rufus, insert the USB, launch Rufus, select the ISO, set Partition scheme to GPT, set Target system to UEFI (non CSM), then click Start. If the installer warns about the file system, accept the recommended defaults.

Shrink the Windows partition next. Right-click Start, choose Disk Management, then right-click the C: volume and choose Shrink Volume. Enter how many megabytes you want to take from Windows, then click Shrink. When that is done, Windows should show unallocated space. If you change your mind before installing Linux, right-click the unallocated space and choose New Simple Volume to give it back.

Find the EFI partition. In Disk Management it usually appears as an EFI System Partition and is small, around 100–500MB. The Linux installer will usually reuse that same partition for GRUB. Do not format the Windows EFI partition unless you know exactly why you are doing it.

Steps

1. Boot from the live USB.
   • Reboot and press the machine’s boot menu key, often F12, Esc, or F10.
   • Choose the USB device listed under UEFI.
   • You should land on the distro’s live menu with Try or Install options.
2. Start the installer and use manual partitioning.
   • Click Install.
   • When asked for installation type, choose Something else or Manual partitioning.
   • That keeps control of the partitions in your hands and avoids overwriting Windows 11.
3. Create partitions in the unallocated space.
   • Create an ext4 root partition. Example: 30GB, mount point /.
   • Create a swap partition if you want hibernation or have low RAM. If you want hibernation, size it to match RAM. Otherwise 2–4GB is fine.
   • Optionally create a separate /home partition for personal files.
   • For example:
     • /dev/sda5 ext4 30G mount /
     • /dev/sda6 swap 8G
4. Set the bootloader target.
   • For UEFI systems, point the installer at the existing EFI partition, not the whole disk. Select the EFI System Partition, normally /dev/sda1, as the EFI receiver.
   • Do not format the EFI partition unless you plan to rebuild Windows boot entries afterwards.
5. Finish the install.
   • Click Install Now and confirm the partition changes.
   • The installer should copy files and then ask for user account details.
   • When it finishes, reboot.
6. Check the first boot and GRUB.
   • GRUB should show entries for Linux and Windows Boot Manager.
   • If you are using Ubuntu, run this in a terminal:

   sudo update-grub

   • You should see a line such as “Found Windows Boot Manager on /dev/sda1”.
   • If Windows boots by default, use the UEFI boot menu or change the boot order in firmware settings.

Commands you will use:

• In the Linux live session:

lsblk --f

• Expected output looks like this:

NAME FSTYPE LABEL MOUNTPOINT
sda
├─sda1 vfat /boot/efi
├─sda2 ntfs (Windows)
├─sda5 ext4 /
└─sda6 swap

• Update GRUB:

sudo update-grub

• Expected: “Found Windows Boot Manager on /dev/sda1”.

Formatting or changing the EFI partition is a state-changing job. If you format it by mistake, stop and use backups. Restoring Windows boot from backup is easier than trying to rebuild lost data.

Checks

Boot both systems and check the files are intact.

Boot checks:

• Boot Linux, log in, and check the disks with:

lsblk
sudo fdisk -l

• Check that the Windows partition is present and not mounted writable by mistake.
• Boot Windows 11 from GRUB. It should start without a disk check prompt. If Windows runs chkdsk on the first boot, let it finish. That can happen if Windows saw an inconsistent filesystem.

Service checks:

• In Linux, check network access and hardware detection. lspci lists devices. If Wi-Fi fails, check rfkill list.
• In Windows 11, open Device Manager and look for missing drivers. Install vendor drivers as needed.

Security checks:

• If Secure Boot is still enabled, test that both systems boot. Many distros support it. If Linux fails with Secure Boot on, go into UEFI settings and disable Secure Boot temporarily. Turn it back on only if you need it and know how to sign kernels.

Bootloader check:

• From Linux, run:

sudo efibootmgr -v

• You should see BootOrder and Boot#### entries. The Linux entry should be present, and probably first if GRUB controls boot.

Data safety check:

• Mount the Windows partition in Linux read-only to check the files:

sudo mount -o ro /dev/sda2 /mnt/windows

• You should see Windows folders such as Program Files, Users, and Windows.

If it breaks

If GRUB disappears or Windows boots straight through, use the Linux live USB and reinstall GRUB.

1. Mount the Linux root partition and EFI partition:

sudo mount /dev/sda5 /mnt
sudo mount /dev/sda1 /mnt/boot/efi

2. Bind the system directories:

for dir in /dev /proc /sys; do sudo mount --bind $dir /mnt$dir; done

3. Chroot into the install, reinstall GRUB, and update it:

sudo chroot /mnt
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
update-grub

4. Exit the chroot and reboot.

You should get GRUB back, with Windows listed again.

If Windows boot is damaged, use a Windows installation USB. Boot the USB, choose Repair your computer > Troubleshoot > Command Prompt, then run:

bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd

For UEFI, assign the EFI partition a drive letter and run:

bcdboot C:\Windows /l en-GB /s S: /f UEFI

That restores the Windows bootloader. It may remove GRUB and force a GRUB reinstall if you want dual boot again.

If a partitioning step removed data, restore it from the backup you made earlier. That is why the backup is there.

The basics stay the same: plan the disk layout, disable Fast Startup, use manual partitioning, and keep recovery USBs for both Linux and Windows. If boot gets messy, the steps above get you back.