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I'm trying to create dual boot on my HDD. (Ubuntu is already installed) When I use my USB stick for a windows 10 boot I can't create a partition. It says I need GPT system. From google I learned that using diskpart I can convert my disk to GPT.

Using diskpart, while I type list disk it shows:

disk 0 - 911GB(total) - 211GB (Free)

Now, If I convert the disk to gpt and then clean my disk, is all my data will be clean? (I don't want my data to be cleaned)

How can I just convert my unallocated 211GB space to gpt? And then install windows?

Emu
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1 Answers1

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Windows is requiring a GPT partition because your BIOS is configured in UEFI mode not in legacy 'MBR' mode.

For future reference, if you can at all avoid it, you want to install windows before installing Linux. The reason is that windows will wipe out your GRUB configuration; there is no installation option that I am aware of where Windows won't at least try to destroy a grub bootloader installation and install it's own bootloader.

Confirm your BIOS is in UEFI mode

An Ubuntu installed in UEFI mode can be detected the following ways (pick 1):

  1. its /etc/fstab file contains an UEFI partition (mount point: /boot/efi)
  2. it uses the grub-efi bootloader (not grub-pc)

  3. from the installed Ubuntu, open a terminal (Ctrl+Alt+T) then type the following command:

    [ -d /sys/firmware/efi ] && echo "Installed in UEFI mode" || echo "Installed in Legacy mode"

If you are in UEFI mode and you want to install windows without having to format (clean) your existing Ubuntu installation, you can resolve this by following these steps. Make sure you read through each step and all links BEFORE starting.

If you don't understand a step in the middle, and have already started you will potentially have a system that doesn't boot either OS until fixed.

Don't try to do this if you aren't prepared to lose all your data on that PC - it can and does happen, even to people who know exactly what they are doing.

  1. Prepare Ubuntu: Follow these instructions provided by Ubuntu:Converting_Ubuntu_into_Legacy_mode to convert your UEFI installation to legacy mode.

    • Check the Secure Boot section as well if that pertains to you and your BIOS configuration - if it is enabled you will likely need to disable it.

  2. Modify BIOS Configuration: Configure your bios to operate in legacy mode. I haven't personally seen a commercial motherboard that didn't provide the ability to switch modes, so it's very likely that yours does as well. The manual for the motherboard will describe how to do it.

  3. Boot into Ubuntu: You should still be able to boot into Ubuntu - you can verify that now if you'd like. If you can't, then you should address Ubuntu not being able to boot into legacy mode before continuing, start here; otherwise continue.

  4. Install windows: In legacy mode you won't be forced to use a GPT partition and it will proceed without issue. After windows is installed grub will not work and you will (temporarily) only be able to boot to windows.
  5. Reinstall Grub: Now follow the instructions found here to reinstall grub and repair your Ubuntu boot.
    • As part of this process you will have to have a bootable Live CD (or USB) of the same version of Ubuntu that you have installed.

Reboot, and you should end up at a grub menu with Ubuntu and Windows as options.

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