So I was told by an IT guy a while back that if I wanted to run Ubuntu without the risk of messing with my existing Windows computer and all of its files, I could simply install and run it off of an external hard drive.

I have been searching for ages for an up-to-date and proper tutorial on how to do this, but have not been successful. I am trying to essentially run Ubuntu on the external hard drive as if it was a persistent USB that I can boot from when plugged in. I have had no success making a persistent USB, so I don't even have much of anything to go off of on my own.

Can anyone help?

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    There's not much science to it. Take out your Windows hard drive so that you won't mess things up, connect installation USB, connect external hard drive, boot, and enter boot selection menu ( usually F8 key, but depends on your computer ). Select USB, and proceed with installation as if it was normal one. Also, consider using virtual machine, instead of actually installing to a drive. VM can be easily deleted and started fresh. Call it dating an OS before actual marriage ;) – Sergiy Kolodyazhnyy Jan 17 '17 at 19:56
  • Just unplug the SATA cable from your Windows HDD during the install, and you'll be fine – You'reAGitForNotUsingGit Jan 17 '17 at 20:10
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    Makes some difference if UEFI or BIOS. BIOS just works, but UEFI only boots external drives from /EFI/Boot/bootx64.efi. And grub/Ubuntu does not create that file. But easy to copy /EFI/ubuntu/shimx64.efi to /EFI/Boot and rename. – oldfred Jan 17 '17 at 20:17
  • Actually I have been running Ubuntu 16.04 from such an expansion usb disk. Read my answer in the link, only caveat is that I tried it in legacy biosnot in uefi, you can pick up legacy bios option from bios menu:askubuntu.com/questions/1131204/… – kenn Jul 21 '19 at 19:15

When you run the Ubuntu installer you have an option to choose the drive you are installing it to. The option will include all the drives that are available at the time you run the installer. If you have USB drives attached they will be included in the choice.

When performing the install, you'll also have the option of choosing the boot drive. If you choose the USB drive as the boot drive during the install, it would be just a matter of ensuring that drive is attached when you boot the computer, and use the computer's BIOS to boot to that drive.

The installation on the USB drive will be no different than and installation on your internal hard drive.

The drive choice for installation will come on the next screen after the one that has the option to Erase disk and install Ubuntu. When you click continue, it will give you a second install screen also titled Erase disk and install Ubuntu. This second screen is the one that has will have the Install Now button.

By the way, even clicking Install Now, you'll still get one more chance to Continue or Go Back. On that last change it will give you an information screen of which device (drive) will be changed and how it will be changed.

UEFI vs Legacy BIOS mode

You have to set your Computer's BIOS mode to match the installation type of UEFI or BIOS for the OS you are booting to.

To make your USB installation more universal compatible as you indicated in your question, you'll best choose Legacy mode for your installation. When I install to a USB drive, I only have the option (from the computers I have used so far) to install in Legacy.

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