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This will be kind of long.

So, I had a Manjaro KDE installation dual booting with Windows 11. I decided I want to install Ubuntu (specifically Ubuntu Budgie) instead of Manjaro. I booted from the live USB, and the install options were:

  1. Install alongside other operating systems (not what I wanted)
  2. Use entire disk (still not what I wanted)
  3. Something else (I selected this)

I deleted the Manjaro partition and used the free space to install Ubuntu. It installed successfully and told me to remove flash drive and press enter. As soon as it boots it says, "unknown partition" and goes to GRUB rescue. I tried a few methods to boot into Ubuntu from GRUB rescue, none were successful. I understand the problem, I deleted the partition that stores files for GRUB. I managed to get to BIOS set up during the split second between pressing the power button and loading GRUB (which automatically goes to GRUB rescue). I changed the settings to use Windows Boot Manager instead of Manjaro. It worked and booted into Windows. Now my question is, how do I install GRUB? If I boot with the live USB again is there a way to install GRUB?

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  • Read man grub-install. Dual Boot advice: I suggest you read https://en.wikipedia.org/wiki/Power-on_self-test , https://en.wikipedia.org/wiki/BIOS , https://en.wikipedia.org/wiki/Master_boot_record , https://en.wikipedia.org/wiki/GUID_Partition_Table , https://en.wikipedia.org/wiki/UEFI . One will have the Answer. Read the others to understand that one.
    – waltinator
    Commented Dec 16, 2021 at 22:44
  • It sounds like you did not install in same boot mode a old install, so old grub will in UEFI or MBR. With Windows in UEFI boot mode, Ubuntu should also be in UEFI boot mode & then installer should have made it default on restart. Some systems like HP will not recognize the change and you have to go into UEFI to change boot order.Only post pastebin link to the Boot-info summary report , do not run the auto fix till reviewed.Lets see details, use ppa version with your USB installer or any working install, not Boot-Repair ISO (unless 21.10) help.ubuntu.com/community/Boot-Repair
    – oldfred
    Commented Dec 16, 2021 at 23:28
  • @oldfred No, it simply failed to install GRUB. Like I said, I made it to BIOS settings, and made Windows Boot Manager the default so that I could at least access Windows. The default was still Manjaro Boot Loader, which was failing. Ubuntu Boot Loader wasn't there, or any other boot loaders. Just Manjaro and Windows. I had just replaced Manjaro with Ubuntu, which is why Manjaro's boot loader was failing. The solution ended up being to reinstall, this time it correctly installed GRUB.
    – Brendan
    Commented Dec 17, 2021 at 20:39

2 Answers 2

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I fixed it! All I had to do was boot the live installer, follow the steps like last time, except when it asks where to install it, select uninstall Ubuntu and reinstall Ubuntu (the installer detects the existing installation of the operating system you're installing, and adds options for reinstalling). That's it! This time it should install GRUB and set it as the default boot loader.

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  • That also often works. New installs or good backups often make reinstall the quickest fix. But you may just have needed to do a grub2 reinstall using live flash drive installer with Boot-Repair or just manually mount ESP & / and reinstall grub.
    – oldfred
    Commented Dec 17, 2021 at 21:52
  • @oldfred That's what I was asking how to do. I didn't know how to install GRUB after the installation.
    – Brendan
    Commented Dec 22, 2021 at 1:05
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After a Windows-update you probsbly have to reinstall Grub2 again. But now you already know how to do that (sudo apt install grub).

Or you can install 'Grub2win' in your Windows, like it says it is Grub for Windows. I have Grub2 installed in it own partition and have Grub2win in my Windows-installation.

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