This question already has an answer here:

I have been trying for a week to install (not live cd) Ubuntu on an external drive.

I am totally new to Linux and would love to try it out. That's why I want to install it on an external drive and not dual boot.

I used two USBs, one with a live Linux system, and another to install it onto. I chose the boot location as the external hard drive when installing Linux. But when I boot the PC (without the drive inserted) GRUB appears and stays there. However when the drive is inserted and I boot the PC GRUB appears and gives me the option to go to Ubuntu.

So it seems as if Ubuntu is installed on the USB, but something important for booting seems to be installed on the PC and therefore when I use the drive on a different PC it doesn't boot (which is the main reason I'm installing Linux).

Please help me fix this!

merged by Marco Ceppi Aug 28 '18 at 15:00

This question was merged with How do I install Ubuntu to a USB key? (without using Startup Disk Creator) because it is an exact duplicate of that question.