Dual booting Ubuntu alongside Windows requires Windows installed first. Shrink its partition, make a bootable USB with Rufus, and choose the alongside-Windows installer option so GRUB manages both operating systems.
One computer, two operating systems, zero performance overhead. Learning how to dual boot Ubuntu alongside Windows is the most practical way to run both environments on a single machine without virtualization. The whole process takes about 30 minutes once the prep work is done, and GRUB handles the boot menu automatically from there. The steps below work for Windows 10 and Windows 11 on any modern UEFI-based PC.
What You Need Before You Start
The requirements are minimal, but skipping any one of them is the fastest way to hit a wall mid-installation. Here is the checklist:
- A PC running Windows 10 or 11 with UEFI firmware (standard on all PCs from the last decade). Legacy BIOS is not supported for Windows 11 dual boots.
- At least 25 GB of free space on the Windows drive. 50 GB is safer if you plan to install multiple apps inside Ubuntu.
- A USB drive (16 GB minimum) for the Ubuntu installer.
- BitLocker off in Windows before installation. Leaving it on can hide the Windows partition from the Ubuntu installer.
- Windows data backed up to an external drive. Partitioning always carries a small risk of data loss, and a backup removes the anxiety.
Step 1: Prepare Windows and Free Up Space
Dual booting works best when Windows already owns the whole drive and you shrink its partition from inside Windows. Start by disabling BitLocker — open Control Panel > BitLocker Drive Encryption and turn it off for the system drive, then wait for decryption to finish.
Next, shrink the Windows partition: right-click the Start button, select Disk Management, right-click the C: partition, choose Shrink Volume, and enter the amount of space in MB (25 GB = 25,600 MB). The result should be a black bar labeled Unallocated at the end of the drive. That is the the space is ready for Ubuntu.
Step 2: Create a Bootable Ubuntu USB Drive
Download the Ubuntu 24.04 LTS ISO from the official Ubuntu site (the file is about 5.7 GB). LTS releases are recommended for dual boots because they receive updates until April 2029. Use Rufus to write the ISO to the USB drive with these settings:
- Partition scheme: GPT (not MBR).
- Target system: UEFI (non-CSM).
- File system: FAT32 (default).
- Click Start and select Write in ISO Image mode if prompted.
Rufus will format the drive and copy the installer files. When it finishes, the USB is ready to boot.
Dual Booting Ubuntu on a UEFI System: What Changes with Windows 11
Windows 11 enforces UEFI and Secure Boot, which changed how dual booting works compared to older Windows versions. Both operating systems must install in UEFI mode with a GPT partition table — the Ubuntu installer handles this automatically as long as you boot the USB in UEFI mode and not Legacy/CSM. Secure Boot may block the Ubuntu bootloader on some systems; if the installer refuses to boot or GRUB fails to appear after installation, enter the BIOS setup (usually F2 or Del during startup) and set Secure Boot to Disabled. Ubuntu 24.04 LTS includes a signed shim bootloader that works with Secure Boot on most PCs, but disabling it remains the most reliable path.
Step 3: Start the Ubuntu Installer From USB
Restart the PC with the USB drive plugged in. Press the boot menu key — usually F12, F10, Esc, or F2 depending on the manufacturer — and select the USB device that has UEFI in its name. Choosing the non-UEFI option will boot the installer in Legacy mode and can prevent the dual boot from working correctly.
Once the Ubuntu logo appears, select your language and keyboard layout, then click Install Ubuntu. Connect to WiFi if you want updates and third-party software installed during setup — it saves a step later.
Step 4: Choose Your Installation Method
This is the critical decision point. Ubuntu offers two paths, and the right one depends on how much control you want:
| Method | How It Works | Best For |
|---|---|---|
| Install alongside Windows Boot Manager | The installer automatically shrinks Windows further (if needed) and creates ext4 root and swap partitions in the free space | Most users who want a quick, hands-off setup |
| Something else (manual partition) | You select the unallocated space, create partitions yourself — root (/) with ext4 at 25 GB+, optional /home, and swap |
Users who want specific partition sizes or a separate /home for easier future reinstalls |
The automated method is safe and uses sensible defaults. If you choose manual partitioning, create the root partition first: click the free space, press +, set size to at least 25,000 MB, mount point /, and format as ext4. Then create a swap partition equal to your RAM size (if you want hibernation) or 2–4 GB otherwise. The installer will detect the existing Windows bootloader and set up GRUB to offer both operating systems.
Does Dual Booting Work With Secure Boot and BitLocker?
Both features can coexist with Ubuntu, but the installation order matters. Secure Boot is hit-or-miss — Ubuntu 24.04 ships with a Microsoft-signed shim that boots on most systems, but if your machine’s firmware is picky, you will see a black screen or a Secure Boot violation error. The fix is to disable Secure Boot in BIOS before installing and leave it off permanently; Ubuntu does not require it the way Windows 11 does.
BitLocker must be disabled before installation. If it remains active, the Ubuntu installer may not see the Windows partition at all, or it may treat the drive as fully encrypted and refuse to partition it. After Ubuntu is installed and GRUB is confirmed working, you can re-enable BitLocker in Windows for that partition. Ubuntu can be encrypted separately with LUKS during installation — look for the “Encrypt the new Ubuntu installation” option — which keeps both operating systems independently protected.
Step 5: Complete Setup and Reboot Into GRUB
After selecting the installation method, set your timezone, create a username and password, and wait 10–15 minutes while the installer copies files. When it finishes, a prompt tells you to remove the USB drive and press Enter. Do that, and the system will reboot.
The screen that appears next is GRUB — a simple text menu listing two entries: Ubuntu (the default) and Windows Boot Manager. Use the arrow keys to pick one and press Enter. If you see both options, the dual boot is working. Windows boots normally with no performance loss, and Ubuntu runs at full hardware speed with native driver support.
Common Dual Boot Problems and Their Fixes
Even when the installation goes smoothly, a few issues can surface later. Here are the most frequent ones and how to resolve them quickly:
| Problem | Why It Happens | How to Fix It |
|---|---|---|
| GRUB missing after a Windows update | Windows update resets itself as the primary bootloader | Boot into BIOS and set Ubuntu as the first boot device, or boot from an Ubuntu live USB and run sudo update-grub inside the installed system |
| Ubuntu installer doesn’t see Windows | BitLocker is still active or the disk is set to Dynamic | Disable BitLocker in Windows; convert Dynamic disks back to Basic using disk management tools |
| USB installer won’t boot | Booted in Legacy mode instead of UEFI | Restart, open the boot menu, and select the UEFI-labeled USB option (not the plain one) |
| Secure Boot error on startup | Firmware doesn’t trust Ubuntu’s shim bootloader | Enter BIOS setup and disable Secure Boot; Ubuntu runs fine without it |
| “No root file system” error | Manual partitioner was used but no / mount point was set |
Go back, select the partition intended for Ubuntu, click Change, set mount point to / and format as ext4 |
The Safer Alternative: Two Physical Drives
Installing each operating system on a separate physical drive eliminates most bootloader conflicts. Windows gets one drive, Ubuntu the other, with each having its own EFI partition. Windows updates cannot overwrite GRUB because they live on different hardware. The installation process is the same — just select the correct drive in the Ubuntu installer — and it is worth considering if your machine has space for a second SSD.
Dual Boot Setup: What Happens After the Reboot
Once GRUB is installed, the system works like this every time it starts: GRUB loads first, shows the menu for 10 seconds, and boots the default selection if no key is pressed. You can change the default OS and the timeout by editing /etc/default/grub in Ubuntu and running sudo update-grub. If you ever want to remove Ubuntu, delete its partitions from Windows Disk Management and run bootrec /fixmbr from a Windows recovery environment to restore the Windows bootloader. The dual boot is fully reversible, which makes it a low-risk way to explore Linux while keeping a familiar daily driver on the same machine.
References & Sources
- Ubuntu. “Install Ubuntu Desktop.” Official step-by-step installation guide covering download, USB creation, partitioning, and dual boot setup.