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Tried to install Ubuntu on an external drive. Took several attempts and eventually got it installed on sdb/sdb1. Unfortunately at some point grub has also been written to the internal hard drive (SDA? I forget).

Unfortunately now I can only boot windows by inserting the Ubuntu disk and choosing windows from the boot options.

The bios reports two boot entries on the main drive (grub and windows) but while I can rearrange devices it doesn't have any function to arrange entries on a device.

If I try to boot the main drive it goes to a grub command prompt.

Trying to boot from a usb stick also fails. Either it ends up in grub or it ends up failing to find bootx64.efi but I've looked and I know that's there. (Something to investigate...)

To complicate things the ubuntu install on the external drive no longer boots properly. It gets to a try window and prompts for login but attempting to login doesn't work.

I can continue to boot off the external drive and call it advanced security :-) but I'd rather not have to. Anyone suggest how I can proceed?

(And before anyone says it, yeah I should have done a full disk backup...)

What I want to do is make a boot entry on the internal drive so it can boot without needing the boot entry on the external usb device. (I'll worry about fixing the ubuntu install later.)

The grub config on the efi partition on the main drive:

search.fs_uuid a36eccd7-fda5-49f2-b981-df13c6de6b27 root hd1,gpt2 set prefix=($root)'/boot/grub' configfile $prefix/grub.cfg

There seems to be no grub directory and no modules. I'm thinking could i edit this and add a reference to bootx64.efi? At the moment it don't have permissions.

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    It is hard to understand, what do you want to do? run Windows with its bootloader from sda and run grub+ Ubuntu from sdb? what is computer name and model and which windows, windows 10, 11, 8? Please edit your question and give the info.
    – amar
    Commented Jun 18 at 16:41
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    UEFI or BIOS install? What version/flavor of Ubuntu. Older versions & flavor automatically installed grub boot loader to first drive, no matter what you select. Newer versions let you choose and it works. You want boot loader on external drive. If UEFI, you should be able to select from UEFI one time boot menu. But if BIOS, you are using MBR on internal drive for grub, not Windows.Please copy & paste the pastebin link to the BootInfo summary report Use updated ppa version with your USB installer or any working install over somewhat older ISO. help.ubuntu.com/community/Boot-Repair
    – oldfred
    Commented Jun 18 at 16:56
  • That's useful information. I made several failed attempts at install. I guess one of them I was careless. It was getting late...
    – user3473715
    Commented Jun 18 at 17:29

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Thanks everyone for your help. I fixed it. I'm sorry that my answer isn't very much Ubuntu related but maybe it will help other newbies liked myself...

I simply downloaded a third party uefi boot config editor and moved the windows entry above Ubuntu. I've been searching for any answer for a week and in the end it took about 5 minutes. In the process I have learned quite a bit about grub and Ubuntu. The Ubuntu on physical disk still doesn't boot but that's another question and in the meantime I've installed one in a virtual box VM. Less risky :-). Thanks again. Hopefully one step closer to getting rid of pesky old windows...

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