How do I boot up Ubuntu on a flash drive without uninstalling Windows?

How do I boot Ubuntu from a USB without installing it on my laptop and without harming Windows?

When I turn off my laptop and I plug in the USB, I want to boot up Ubuntu.

When I turn off my laptop and remove the USB, I want to boot up Windows.

1. Create the Ubuntu LiveUSB: https://ubuntu.com/tutorials/create-a-usb-stick-on-windows

2. Boot into your BIOS. Select the USB as your boot media.

   • Remember to change the selection back during a following boot so Windows will boot.

   • Many BIOS let you set a boot order or boot priority. Move the USB to the top of the list. That way, if the USB is inserted then Ubuntu will run. If the USB is not inserted, Windows will run. Much easier than changing the setting every boot.

3. When the LiveUSB boots, select the "Try Ubuntu" environment, which WON'T install Ubuntu. Don't select "Install Ubuntu", which will do exactly what it says.

   • The "Try Ubuntu" is a fully-featured, working Ubuntu system. However, it's read-only. If you want to save any data, you must save it on some other media.

   • It's possible to create LiveUSBs that have a writable partition, so saved data and updates and customizations are preserved. See https://wiki.ubuntu.com/LiveUsbPendrivePersistent.

The "Try Ubuntu" environment is provided so you can thoroughly test your hardware and your workflow before deciding if you want to commit to Ubuntu. It's not tested for long-term use, though some folks do use it for that.

Persistent Install vs Full install

Ubuntu can be installed to a USB in different ways. A Live install does not save between sessions. A Persistent install extracts the OS from a compressed file and saves data to an overlay file or partition each session, and a Full install installs the complete OS to the USB just like an install to internal disk.

Comparison between Persistent and Full install USB

Advantages of a persistent install:

1. You can use the persistent pendrive to install Ubuntu to another computer.

2. A persistent install takes up less space on the pendrive.

3. You can reset the pendrive by overwriting the old casper-rw file with a new one.

4. The install to pendrive takes less time.

5. Slightly less wear on the drive.

Advantages of a Full install:

1. You can update and upgrade.

2. If you have problems or wish to modify, the solution is the same as with an internal install, (You can ask for help in the forums).

3. No ugly startup / install screen.

4. Better security, you can use full encryption

5. You can use proprietary drivers.

6. Swapfiles and partitions work and Hibernation can be enabled.

7. Many persistent installs are limited to a 4GB casper-rw and a 4GB home-rw persistence file, to get more persistence requires persistence partitions. Once casper-rw is full, the drive will not boot.

8. More efficient usage of disk space. Does not require reserved space for persistence.

9. Faster boot, no automatic disk checking or Try Ubuntu/Install Ubuntu screen.

10. You can run VBox and use virtual machines.

11. Generally faster boot than Live or Persistent USB's.

12. More stable, better for day to day use. I have run Ubuntu off a flash drive for 5 years making only LTS upgrades.

Note that once booted, both methods run at about the same speed. If the computer has lots of RAM Ubuntu should run mainly in RAM and there will not be a big difference between running off internal HDD and USB3 flash drive f.

Full Install Method

A quick and easy method to flash a Full install to USB can be found here: Easy Full Install USB that Boots both BIOS and UEFI

A more traditional methods for creating a Full install USB from scratch can be found here: How to Create a Full Install of Ubuntu 20.04 to USB Device Step by Step

Persistent install method

The following tools can be used to make a Persistent install USB: mkusb - https://help.ubuntu.com/community/mkusb, Rufus - https://rufus.ie/en/, Universal USB Installer - https://www.pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/, Ventoy - https://www.ventoy.net/en/index.html, YUMI- https://www.pendrivelinux.com/yumi-multiboot-usb-creator/. and others.

There is an official tutorial that describes how to "Try Ubuntu". This provides instructions on using a live session of Ubuntu which does not affect your installed system, unless of course you use that live session to explicitly make changes to files on your hard drive.

First, you will need to create bootable Ubuntu media.

Fortunately, there are also official tutorials for creating media using Windows, Mac, and Ubuntu.

When you boot the USB, you will need to consult with the documentation for your computer's motherboard because different motherboards do not all have the same process to select bootable media.