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

[Ralf Corsepius]

On 03/30/2011 02:30 PM, Lennart Poettering wrote:
> On Wed, 30.03.11 18:04, Rahul Sundaram (metherid at gmail.com) 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.

It's in the preface of the root file system section:

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

<cite>
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.
</cite>