Some firmwares will present the USB host controller as UHCI (USB 1.1) at boot time. It's best to understand what it does and disable it if you plan on writing to your Windows drive from Linux. This feature takes some shortcuts when it comes to booting and also makes the NTFS filesystem remain in a dirty state, making it unwriteable from Linux. It's worth noting that Windows 8 and 10 have an Fast Startup or Fast Boot feature. It also has an option to support Intel Rapid Start Technology which does get in the way of booting to multiple OS. For example, my Intel NUC has an option called Fast Boot which won't let me choose an alternative boot device at startup. Many boards come with some sort of 'fast boot' or 'boot optimization' options. I suggest turning off Secure Boot if possible. Even though Ubuntu does support Secure Boot (it comes with signed bootloaders) I have no idea if my method uses the signed bootloaders or not. I have only tested these instructions with Secure Boot turned off. Below is a selection of problems that got me moderately stumped along the way. Given enough experience and patience you can work around them. Nowadays, in the interest of security, performance and backwards compatibility, there are many semi-hidden options and features which can get in your way. Having a dual- or multi-boot system isn't as straightforward as it used to be a decade ago.

You are going to make changes to your computer. Remember to take backups of all your critical files and folders before continuing.

Windows System Repair Disc (a bootable USB drive with Windows recovery tools which you can make yourself) or a Windows installation or rescue CD-ROM / DVD-ROM.

Very easy to create using Rufus on Windows. For those of you worrying about performance, the USB 3.0 port is faster than the maximum transfer rate of any SSD I've seen to this date. I used a USB 3 drive enclosure with a cheap 256Gb SSD.

It is tough, but I'm writing this from my portable Ubuntu Linux installation running off a USB-attached SSD! What you need Moreover, all the preparatory work has to be performed using a single-boot Windows computer without ending up having a dual boot system. That entails having the Linux installation on an external, USB-attached hard disk drive which can boot with relative ease on any UEFI-enabled PC (driver compatibility notwithstanding). Moreover, a decent, up-to-date, bootable Linux environment is a great backup in case all of my other computers are broken, infected or stolen. Sometimes a virtual machine won't cut it for me typically due to memory, disk and performance limitations. I regularly have the need to try things out on Linux.

Create portable ubuntu usb