What's this /run directory doing on my system and where does it come from?

[Xose Vazquez Perez]

Lennart Poettering wrote:

> Also, can somebody point me to the place where the FHS would say "no
> other directories below / are allowed"? I can't find that. And hence
> this change is perfectly FHS compliant.

http://www.pathname.com/fhs/pub/fhs-2.3.html#PURPOSE2

Applications must never create or require special files or 
subdirectories in the root directory. Other locations in the FHS 
hierarchy provide more than enough flexibility for any package.

*Applications*