Similar to this question, but a bit different I think? How to remove Ubuntu from EFI partition
I've installed Ubuntu 18.04 on a 32GB usb stick, with its own EFI partition and swap partition on the stick.
However, when I plug it into a machine and boot Ubuntu off it, it decides to install its own bootloader or boot option to the on-board hard drive. I don't quite know the mechanism for this - when I start to boot from the USB drive, the first time some text comes up briefly on screen about failing to boot, then disappears; the second time it boots fine.
I've tried this on two separate Windows machines, neither of which have any other operating systems: 1. MBR-based 64 bit windows 7 desktop 2. UEFI 64 bit windows 10 laptop, with Secure Boot enabled
So far as I understand it, I should be able to install onto the USB stick with an EFI partition so that it doesn't need to do anything with the internal EFI partition at all - am I correct in this?
I explicitly want to make no changes to the internal hard disk, especially on the laptop, as it's a company laptop. I'm aware I can probably remove the bootloader entry from the internal EFI partition using efibootmgr or something, but it would be a faff to do that repeatedly.
Tl;dr: I have a USB Ubuntu 18.04 with an internal EFI partition. How do I use this without it editing the internal EFI partition or boot menu of the computer I boot it with? I explicitly want to avoid an appearance of a dual-boot prompt or internal GRUB2 installation
For info, install method was:
1) Formatted USB with Gparted with appropriate partion types & sizes
2) Disconnected all hard drives from my desktop
3) Plugged in Ubuntu 18.04 live usb stick and the USB I wanted to install to such that it was the only hard drive, with legacy compatibility switched off, and installed 18.04 onto it selecting efi, root and swap partitions as appropriate.
