Thinkpad T420 won't boot from USB

[Bo Berglund]

On Fri, 22 Oct 2021 16:48:02 +1000, Phil Fraser <phillor9 at gmail.com> wrote:

>I now have my SSD's partition table set to DOS mode (instead of GPT) and 
>have Windows 10 installed once again and have shrunk the partition ready 
>to install Linux. The problem is that the laptop will not boot from a 
>USB stick except for the one that I prepared with Rufus. This, I'm sure, 
>has been the root of my problem in getting Windows and Linux to coexist 
>on my SSD.
>
>My usual routine is to press F12 and then select USB. This works with 
>the Rufus prepared USB stick but no other USB sticks. Selecting USB 
>causes the screen to blank for a few seconds and then the menu reappears. 
>I also tried setting the first item in boot order to USB HDD. The USB 
>stick is ignored and the boot continues from the SSD.
>
>The only way that I can get my Linux prepared USB stick to boot is to 
>select "both" (UEFI/Legacy). I think this is how got myself into so much 
>trouble, although the installation of Windows and Linux on my mechanical 
>disk went without a hitch.
>
>I have searched the Internet for a solution but all that I've found is 
>others asking the same question. Obviously it can be done because I'm 
>not the only owner of a Thinkpad T420.

I had similar problems when trying to convert a new Lenovo PC to a Linux
server...

It is a Lenovo IdeaCentre 3 PC which came with Windows 10 pre-installed.
It uses UEFI Secure Boot, which messes with the way booting is done.
I had to go into the UEFI configuration this way to change it:

- With Windows running press shift
- Select Start Menu / Power / Restart
- Now select Troubleshoot/Advanced Options/UEFI firmware settings"
- Select category "Security" or "Boot" (might be named differently)
- Find "Secure Boot" and disable it.
- Save settings and reboot

Next in order to actually boot from USB:
- With Windows running press shift
- Select Start Menu / Power / Restart
- On the screen "Choose an option" select "Use a device"
- Look for your USB device (indicated by name on the button)
- Click it and the PC will boot from it.

The above is valid on my IdeaCentre but may be somewhat different on another
model.
Here is a link to the page I found that enabled me to actually install Ubuntu in
dual-boot mode:
https://www.pcworld.com/article/422665/how-to-install-linux-on-a-pc-with-secure-boot-enabled.html

HTH


-- 
Bo Berglund
Developer in Sweden