Installing Ubuntu alongside Windows lets you choose an operating system when your computer starts. The process can preserve your Windows files, but it changes disk partitions and boot settings, so a mistake or hardware failure can cause data loss. Back up your files first, check how Windows is configured, and proceed only when you understand which disk space the installer will use.
This guide covers preparation, UEFI, BitLocker, Secure Boot, USB installation, and recovery steps. Installer screens can vary by Ubuntu release and computer, so follow the instructions for the version you download if they differ.
Key takeaways
- Make and verify a separate backup before changing partitions. A dual-boot setup is not a substitute for a backup.
- Install Ubuntu in the same boot mode as Windows, normally UEFI on newer computers.
- If BitLocker or Windows Device Encryption is enabled, save the recovery key and address encryption before resizing or installing.
- Use Windows Disk Management to shrink the Windows volume and leave the resulting space unallocated for Ubuntu.
- Read every installer disk-selection and partitioning screen carefully. Choosing or formatting the wrong partition can erase data.
1. Prepare Windows and back up your data
Copy important documents, photos, project files, and other irreplaceable data to an external drive or another backup location. Open a few files from the backup to check that it worked. If you use a backup program, make sure you know how to restore files from it.
Also prepare for the possibility that the computer may not boot as expected after installation:
- Create Windows recovery media or make sure you can access the recovery tools for your device.
- Keep your Windows account details and any required recovery keys somewhere separate from the computer.
- Connect a laptop to power and avoid interrupting installation once disk changes begin.
- Check that you have enough free disk space for Windows and Ubuntu. The space Ubuntu needs depends on your applications and files; leave room for updates and future growth.
Check whether BitLocker or Device Encryption is enabled
BitLocker and Windows Device Encryption protect data by encrypting the Windows drive. Check Windows Settings or the BitLocker management page to see whether encryption is enabled. Save the recovery key somewhere you can access without booting Windows.
An Ubuntu installer may not be able to shrink or install alongside a Windows partition that remains encrypted. Before changing partitions, follow the current guidance for your Windows edition and Ubuntu release. You may need to suspend protection temporarily or decrypt the drive before resizing it. Suspending protection is not the same as decrypting: follow the instructions for the action you choose, and do not proceed until you understand the security implications and have the recovery key.
Firmware, boot configuration, or partition changes can sometimes cause Windows to request the BitLocker recovery key at startup. Having that key available is essential. Do not clear the TPM or change unrelated firmware settings as a workaround.
2. Check UEFI and Windows boot mode
Most current Windows computers use UEFI firmware and a GPT-partitioned disk. Confirm the setup rather than assuming:
- In Windows, open System Information.
- Find BIOS Mode. If it says UEFI, boot the Ubuntu USB in UEFI mode too. If it says Legacy, investigate your system configuration before changing boot modes.
- In Disk Management, inspect the Windows disk and its partitions. A UEFI Windows installation commonly has a small EFI System Partition, but do not delete or format it.
Windows and Ubuntu should normally be installed in the same firmware boot mode. Mixing UEFI and Legacy/CSM modes can leave the operating systems using separate boot methods and make the startup menu confusing. Avoid switching firmware modes casually, because changing the mode Windows expects can prevent it from starting.
3. Make room using Windows Disk Management
The safer general approach is to shrink the Windows volume from within Windows, then let Ubuntu use the unallocated space.
- Open Disk Management in Windows.
- Identify the correct disk and the Windows volume, often labeled
C:. Double-check the disk before making changes, especially if the computer has more than one drive. - Right-click the Windows volume and select Shrink Volume.
- Choose a shrink amount that leaves Windows enough space for its files, updates, and applications.
- Confirm the change and check that the new space is shown as Unallocated.
Do not create a new Windows-formatted volume in that space. Leave it unallocated for the Ubuntu installer. Do not delete recovery, EFI, or other partitions to make room. If Windows cannot shrink the volume enough, stop and investigate rather than forcing a partition change; encryption, immovable files, or disk errors can affect what Windows allows.
Partition changes always carry risk. If Disk Management shows an unexpected layout, the disk uses a complex configuration, or you are unsure which volume is which, get help before proceeding.
4. Create and boot an Ubuntu USB installer
Download an Ubuntu Desktop ISO from the official Ubuntu website and use a reputable USB-writing tool to write it to a USB drive. Writing an image typically erases the USB drive, so copy anything important off it first. If the download page provides a checksum and you know how to verify it, checking the downloaded file can help detect an incomplete or altered download.
Restart the computer and open its one-time boot menu, using the key shown by the manufacturer. Select the USB entry that corresponds to the same mode as Windows—usually the entry marked UEFI. The exact key and menu labels vary by computer.
Choose the option to try or install Ubuntu. If the live session loads, you can check basic hardware compatibility before starting the installation. When ready, launch the installer and proceed carefully.
Secure Boot
Do not assume Secure Boot must be turned off. Ubuntu releases commonly support Secure Boot using signed boot components, though compatibility can depend on the release, hardware, drivers, and any additional kernel modules you need. If the installer or a required driver reports a specific Secure Boot problem, consult the instructions for that Ubuntu release and device before changing the setting.
If you temporarily disable Secure Boot, understand how to restore the original firmware setting afterward. Changing firmware settings can also trigger a BitLocker recovery prompt, so keep the recovery key available.
5. Install Ubuntu into the unallocated space
The installer may offer an option such as installing Ubuntu alongside Windows, but the exact wording and availability vary. If you see that option, check the displayed disk and partition changes before confirming. Make sure it refers to the unallocated space you prepared—not a Windows partition or another drive.
If the installer does not offer an alongside option, do not guess at manual partitioning. Manual setup requires identifying the correct disk, preserving the existing EFI System Partition, and creating suitable Linux partitions in the unallocated space. Formatting the wrong partition can destroy Windows data or prevent Windows from booting. If you are not experienced with partition layouts, stop and consult the documentation for your Ubuntu release or ask someone qualified to review the layout.
Before the final confirmation, review the summary closely:
- Confirm the intended physical disk.
- Confirm that Windows partitions are not selected for formatting or deletion.
- Confirm that Ubuntu will use the unallocated space.
- Stop if the proposed changes do not match what you expect.
Once you confirm, the installer writes partition and boot information. Do not power off the computer during this stage. Follow the prompts to complete setup and restart, removing the USB when instructed.
6. Test both operating systems
After installation, the computer may show a boot menu, or it may start one operating system by default. Test Ubuntu and Windows separately. In Windows, check that your files and applications are present. In Ubuntu, check basic hardware such as Wi-Fi, sound, display, and input devices.
If Windows starts directly and you cannot see Ubuntu, the installation may still be present. Check the computer's one-time boot menu for an Ubuntu entry before changing partitions or reinstalling. Boot-menu behavior depends on firmware settings and the system's boot configuration.
Recovery options if something goes wrong
Windows asks for a BitLocker recovery key
Enter the recovery key you saved before installation. If you cannot find it, use the account or organizational process through which the key was stored. Avoid repeated firmware changes while locked out; changes to boot configuration can complicate recovery.
The computer starts Windows but not Ubuntu
Use the firmware's one-time boot menu to check whether an Ubuntu boot entry is available. If it is, select it and then review the firmware's boot order if you want to change the default. Do not delete Windows boot entries or alter partitions just to make the menu appear.
The computer does not start Windows
Use Windows recovery media or the computer manufacturer's recovery tools. Choose repair options rather than reset or reinstall options if you need to preserve existing files, and read each prompt before confirming. If important files are not backed up, avoid formatting or reinstalling until you have a recovery plan.
A partition looks missing or has the wrong size
Stop making changes. Do not create, delete, or format partitions to see whether the issue resolves. If data matters, seek help from a qualified technician or data-recovery professional before writing more changes to the disk.
Common mistakes to avoid
- Skipping the backup: A successful installation is not guaranteed, and backups protect against more than installer mistakes.
- Shrinking the wrong volume: Confirm the disk and Windows volume before using Disk Management.
- Formatting the EFI System Partition: It may be needed by Windows and Ubuntu. Do not format or delete it unless a carefully planned, release-specific procedure explicitly requires it.
- Booting the USB in the wrong mode: Match the USB boot mode to Windows, normally UEFI.
- Treating unallocated space as a partition: Leave it unallocated in Windows for the installer.
- Ignoring BitLocker: Save the recovery key and understand whether encryption must be suspended or decrypted before resizing.
- Assuming Secure Boot must be disabled: Check whether your Ubuntu version and required drivers support your setup before changing firmware settings.
- Clicking through the partition summary: Stop if the proposed changes are unclear or would affect Windows partitions.
Conclusion
To install Ubuntu alongside Windows, prepare a verified backup, check encryption and boot mode, shrink the Windows volume with Disk Management, and leave the free space unallocated. Boot the Ubuntu USB in the matching mode and confirm every proposed disk change before accepting it. If the installer layout does not clearly preserve Windows, stop and get help rather than risking files you cannot replace.