If I encounter a situation where I suspect my machine's RAM might be going bad, I might need to launch memtest86+ to check it. How can I do this using Ubuntu? Are there different methods for launching it whether Ubuntu is already installed?
* (This is intended to be a canonical question easy for new users to follow.)
memtest86+ comes default with Ubuntu and you can try it from live CD or from any installation of Ubuntu. Here are the steps:
While booting press (better hold down) the Shift key to bring the grub menu that looks like the following image:
As you can see there are some options to choose from (this will vary from installation to insatllation), the one to look for is the third option in this screenshot i.e. Memory test (memtest86+), which will be there in the grub menu along with other options.
From the grub menu go to the appropriate option to select i.e. Memory test (memtest86+) and press Enter.
Now you will see a blue screen indicating that the memtest is running:
Now you can press c for more configuration options:
To exit from the memtest86+ session you can press Esc any time. There is no certain rule that how many passes you would run but the more the better.
Here is an image (taken from here) showing that errors were encountered i.e. the test is failing in some memory locations (pointed out in the red portion) indicating the locations might have problems. If your memory does not have any problem then you won't get any red portion.