Summary: it seems that memtest86+ won't run under UEFI. You need to switch to "legacy" boot and use an appropriate CD/DVD/USB stick to supply memtest86+. I often run memtest86+ when I get new RAM. This increases my confidence that the RAM isn't busted and is compatible with the machine it is installed in. Running it overnight seems long enough without interfering with my use and enjoyment of the computer. I even run it on a brand-new machine as one of the confidence building measures. Well, that's what I used to do. I've not taken the time to do it recently. But I wanted to run it last night because I bought some (mislabelled!) RAM at the NCIX warehouse sale on Saturday. Ubuntu lets you install memtest86+ as a package (it may be a default package, I don't know). But you cannot run it under Ubuntu, you have to boot into it. When you install the package, it adds a grub entry to let you boot into memtest86+ instead of Ubuntu. Yet on my machine there was no such entry. Reading the script that generates the entry, I found that memtest86+ must be booted in 16-bit mode, i.e. old-fashioned BIOS, and not UEFI. So the script doesn't bother to generate the entry on a UEFI system (silently). To run memtest86+, you have to switch the system firmware to use "legacy" booting (old-fashioned BIOS/MBR). On my machine, you cannot enable both MBR and UEFI booting: you need to choose one. Once I switched to legacy booting, I could no longer use the Ubuntu on my hard drive since it was set up for UEFI. I used a Ubuntu installation DVD -- it has an early option for running memtest86+. It turns out that Fedora 21's live/install image has a newer memtest86+ than Ubuntu 14.04: 5.01 vs 4.20. The newer one lists the DIMMs or SODIMMs present on the system.