I'm looking for the memtest option on the 64-bit version of the Ubuntu 12.04 live CD, but the only options I have are "Try Ubuntu without installing", "Install Ubuntu", and "Check disc for defects". What am I missing?
Edit: This question is relevant for the current versions of Ubuntu (amd64 alias 64-bit, which work in UEFI mode). The boot menu option 'Test memory' is only available in BIOS mode.
Best Answer
Memtest86+
If you boot your computer in BIOS mode (alias CSM alias legacy mode), memtest86+ works.
But if you boot your computer in UEFI mode, memtest86+ will not work, because it is a 16-bit program.
www.memtest.org
Memtest86
The original branch, memtest86 (without plus), works in UEFI mode. There is a free version (but I don't think it is open source, and for this reason not available to include in linux distros).
www.memtest86.com
Memtest via Ubuntu's boot menu
Memtest86+ is included in most Ubuntu iso files, for example
There is an option 'Test memory', when you boot your computer in BIOS mode (alias CSM alias legacy mode) from a DVD disk or USB pendrive with a cloned copy from the iso file.
In Ubuntu 16.04.x LTS systems installed in BIOS mode, there are also options 'Test memory', when you boot your computer (via the grub menu).
But when you boot your computer in UEFI mode, there is no option to use Memtest86+ (because it would not work).
Standalone Memtest86+ image file
If you have an old version of Memtest86+, you can test 4 GiB of RAM. If you have more than 4 GiB RAM in your computer, you need version 5.01 or newer.
(In September 2020 there is also a beta version, 5.31b.)
You may want a small standalone Memtest86+ iso file or other image file in order to create a live USB drive.
I did not find any file at www.memtest.org/#downiso, that is easy to install to USB in linux. The iso file 'memtest86+-5.01.iso' is not a hybrid iso file and cannot be made into one.
It is a very barebone iso file. I tested in VirtualBox, and it works as a CD.
But there is an 'Auto-installer for USB Key (Win 9x/2k/xp/7)' at
www.memtest.org/download/5.01/memtest86+-5.01.usb.installer.zip
I extracted it to a USB pendrive in Windows and cloned this system to a compressed image file and uploaded it to
dd_memtest-plus-5.01_33M.img.xz
which can be extracted directly in linux by mkusb,
dusand Disks aliasgnome-disks(and in two steps, extracting and cloning, with other cloning tools, that accept the extracted file as an input file).After installing mkusb and/or dus, you can do it via Dash or the menu entry or with the following command line