Linux on a Windows 10 Fujitsu Lifebook T939

I wanted to install linux, in particular Xubuntu, alongside Windows 10 Pro on my new Fujitsu Lifebook T939 laptop. Here is how I did it. It worked for me; your results may vary.

First I downloaded an .iso install image of the linux system I wanted, which was Xubuntu 18.04 LTS.

Next I used a linux installation on my old Windows Vista Fujitsu laptop to create a linux live image on a USB stick with persistence and Windows-visible storage. This allows me to both install linux or run linux on any Windows computer without installing it. Note that any existing stuff on the USB stick will be lost. So move it elsewhere. (But you can later put at least some of it back in the "usbdata" partition that will be created on the stick.) Note that the next steps require an existing Ubuntu or Debian type linux; otherwise you will have to do something else to create an install USB stick; google it.

• Without inserting the USB stick, use "lsblk" to see what drives you already have (sda..., sdb..., ...). Insert the stick and use "lsblk" again. The newly added drive must be the stick. Make sure it is; you do not want to overwrite the wrong disk!!
• To install mkusb, in a terminal do:
  sudo add-apt-repository ppa:mkusb/ppa
  sudo apt-get update
  sudo apt install --install-recommends mkusb mkusb-nox usb-pack-efi
  
• Now run mkusb from "System", selecting "Yes" for "dus", "Install (make a boot device)", "persistent live (Debian or Ubuntu)", select the linux .iso installation image you should already have downloaded from the web, and "Upefi".

Now setup Windows 10, make space on the system disk for linux, and make a system disk image and bootable disaster repair disk. Get your Bitlocker key. See the relevant web page, then return here.

• Make sure you have your Bitlocker key.
• First check the documentation for your computer for which key to use to enter the computer BIOS. In my case that was F2, while F12 produced the BIOS menu. Then turn off the computer. Put the live USB stick in the computer and turn it on. When the manufacturer name is visible, hit F2 or whatever, and change the boot order so that the USB stick is enabled and is first. Also go into the security settings or whatever, and disable secure boot. (After the linux installation is complete, you must enable it again or Windows will not boot.) Then save and exit to boot into the USB stick.
• When the live linux is booted, select the "Install" button. Follow the prompts.
• The most tricky step in the installation is how to install linux to the system disk. Do not erase your entire disk!! You would lose Windows. Because of the free space you created by shrinking the Windows C: partition, you should be given an option to install linux in addition to Windows. Consider taking that. Actually, I wanted to leave some free space so that I can extend either Windows or Linux later when I run out of space. So I took "Other" from the choices. Note that this is a tricky business, you will be thrown into disk partitioning! Do not mess that up, or you could still lose Windows! I right-clicked the free space, clicked "Add" and added 4 GB (4,000 MB) of swap space. Since the memory on my machine is more, 16 GB, that means that I cannot hybernate linux. But I never do that anyway. If you have only 8GB of memory, 3GB of swap should be equivalent to my choice. I selected to put the swap at the end of the free space, so that I can still expand the Windows C: drive later if needed. Then I clicked the free space again, added a suitable amount of ext4 space for linux and my linux files, mounted as "/", again at the end of the free space. Ubuntu says you need a minimum amount of 25,000 MB for 18.04 LTS, but I used much more, while still leaving a suitable amount of free space between linux and Windows C:.

After installation, turning off the computer with linux, removing the USB stick, and turning the computer again, going into the BIOS to restore secure boot, and trying to restart Windows, I got a nasty message from Bitlocker that something had changed. Selecting "Other" and entering my Bitlocker key (about a hundred digits; avoid typos), that was fixed and Windows rebooted. Quite a relief. And linux was also bootable. All OK.

Note: In the BIOS boot order, "ubuntu" was put in front of the USB drive. I put the USB drive first again making ubuntu second.