[Post-Install] ubuntu disaster, can I install it without a boot loader

[jlittle]

I wanted to install Ubuntu 25.10, to see if my btrfs problem occurred there.

I couldn't see a way to install without specifying a drive for the boot loader, nor could I install to a btrfs without formatting it; the format check would not uncheck. So I moved what was in use off an old SATA SSD into my main btrfs on NVMe, checked it out there, and proceeded to install to the SATA SSD. I thought it would hijack the boot order, but I'd be able to fix that with efibootmgr.

Oh no, the Ubuntu install scribbled over all the Kubuntu entries, leaving them non-functional, while creating 5 entries for itself! Aargh! The computer would now only boot Ubuntu! I could reach my gentoo install, if I hadn't deleted it years ago. My attempts to change the boot order were ignored, and the boot order changed back.

Eventually I concocted a set of grub commands that got me back to Kubuntu, but I'm scared to reboot now.

Is there a way to install Ubuntu without it screwing up my boot? Is there a way to run it without screwing up my boot?

[oshunluvr]

You could try one of these: ubiquity --no-bootloader or subiquity --bootloader=none

I usually just point it at a different drive or partition, but with EFI it's gonna find that EFI partition and muck with your entries.

Another idea: Install to a VM using BTRFS, then copy the subvolume(s) to your system drive. Probably have to use a USB stick to make it easy - attach the USB to the VM, use "btrfs send" to a file on the USB drive, mount the USB drive on the system, and "btrfs receive" to your host btrfs file system. Then boot it with a custom grub entry. It looks like a plain vanilla Ubuntu install is abround 11gb.

I honestly don't know if all that would work. I have virtually no EFI knowledge.

[oshunluvr]

If this is about USB drives, can you just attach them to a running VM or live session and test that way?

[jlittle]

If this is about USB drives, can you just attach them to a running VM or live session and test that way?

I was not 100% that using a live session would be conclusive. It does appear that it would have, and I could have saved myself a lot of trouble.

[jlittle]

You could try one of these: .... subiquity --bootloader=none

That looks very promising. I might repeat the install; even if I correct the damage that the first install did, if I boot it, it might screw things up again. I suppose I could uninstall grub from it altogether.

[INVICTRA]

I sometimes pass-trough my SATA SSD to a VM and install Kubuntu and configure it there. After that I can try it on my metal direct by switching bootloader in the uefi menu of my motherboard.

[jlittle]

.... subiquity --bootloader=none
That looks very promising. I might repeat the install; even if I correct the damage that the first install did, if I boot it, it might screw things up again. I suppose I could uninstall grub from it altogether.

No, that command is not available. subiquity is a snap, but is not in /snap/bin or anywhere else on the $PATH.