Install bootable Ubuntu on external SSD without changing Windows 10

At work I have to use Ubuntu sometimes but I'd prefer to stick to Windows and don't want to have a dual boot setup. I don't really know if this is possible, that's why I am asking here before breaking my OS. I want to install Ubuntu on an external SSD Harddrive that will be connected to my computer via a USB3 port. When the SSD is plugged in I'd like the computer to directly boot into Ubuntu, whilst booting to Windows 10 when the harddrive is unplugged. In addition to that I'd like to have some space to share data between both operating systems.

I tried to search to problem online but came up only with dual boot solutions.

So is it possible to achieve what I want and can someone maybe show me a tutorial how to do it?

2 Answers

This is a summary of the accepted answer of the Ask Ubuntu post
How to install Ubuntu on portable external Hard Drive?

• Create the Ubuntu live installation media and use it to boot your computer and choose Try Ubuntu
• Plug in the external hard drive
• Start gparted. In most cases, the internal disk will be sda and the externalsdb, but this is not guaranteed.

• Partition the external disk into one or two partitions and note their numbers:

  • If you need a swap partition, format it as linux-swap
  • The rest of the disk format as ext4

• Start the Ubuntu installer from the icon on the desktop or on the launcher. When asked how to install, choose Something Else.

• In the partition editor, highlight the ext4 partition and click Change. Follow the dialogs to:

  • Use the partition as ext4
  • Mount to /
  • Format

• Still in the editor, highlight the swap partition and click Change and choose linux-swap

• Change the installation of the bootloader to the external disk, most likely/dev/sdb. It is important not to overwrite the bootloader on the internal hard drive.

• Double-check your partition choices, then click Install Now.

• Set the USB disk as the first in the BIOS boot order.

From now on, to run Ubuntu boot the computer with the USB plugged in. The boot menu on the USB will show both Ubuntu on the external drive and Windows on the internal drive, and you may choose the one you want.

If you boot without the USB, you will boot into Windows normally.

For another possibility using the Windows Subsystem for Linux (WSL), see the article
How-to Install WSL Distros On External Disks

Well, if you only want to do that just install Ubuntu on the harddrive and change the BIOS settings to boot from the harddrive. When the drive is present the system will boot from this device, if not boot from the local hard drive.

I used Ubuntu on work too, and in order to have both I got a Virtual Machine with Linux having Windows as a host.