My Linux server rebooted spontaneously and then decided to kernel panic.

Running memtest off a bootable Gnome 3 Live USB system:

Diagnosis: dead RAM stick. With only one stick, memtest even crash on test 6, while the other just pass.

The good news is that the motherboard support single channel. The second good news is that it is lifetime warranty. Requested a RMA.

The bad news: I might have to return both as they are paired leading to eventually a longer downtime. :-/