I recently had a problem where my Arch Linux Fn sound volume keys quit working. I looked high and low and could not find a solution.
head space and timing
This is a military term related to ensuring the bolt and head space for the M2 .50 caliber machine gun are in alignment. This must be done correctly, or the weapon can explode during operation. It also means a person who’s screwed something up because they failed to check what they were doing before they did it.
~ head space and timing, Urban Dictionary