Downloaded the Ubuntu 16.04.2 .iso
install disk and flashed it onto a USB stick.
Booting on the USB stick, there is no memtest86+ option (along with "Try Ubuntu").
Is there a way to add it to the install options?
(it's for a UEFI boot PC running normally Windows, its owner does not want to install Ubuntu. "memtest86+" is completely free (unlike "memtest86"), but is quite old, and does not offer a UEFI boot – this is why having it within the Ubuntu options makes things easier)
Best Answer
Memtest86+ does not work in UEFI mode
Memtest86+ does not work in UEFI mode because it is a 16-bit program. But if you can boot the computer in BIOS (CSM, legacy) mode, it works.
See this link
Where is the memtest option on the Ubuntu 64-bit live CD?
Memtest86 works in UEFI mode
There is another version, the 'original' but now not FOSS version memtest86, and it works in UEFI mode. There is a commercial version and a free version (no cost, but not open source code).
See this link
www.memtest86.com/download.htm
Adding newest freeware memtest86 to UEFI Grub2
Here is a great tutorial on how to add the freeware memtest86 to UEFI Grub2. It's especially useful if you are working on a remote machine, and inserting a physical usb is out of the question.
See this link for the Ubuntu oriented tutorial.
https://www.yosoygames.com.ar/wp/2020/03/installing-memtest86-on-uefi-grub2-ubuntu/
See this link of an example of doing this on a remote server, but based on the above tutorial.
https://unix.stackexchange.com/a/632700/253599