From the 'Now You Know' files:

We've all known for some time that Facebook's infrastructure is for the most part running on Linux.

What I didn't know until very recently was which Linux distribution Facebook was using. I caught up with Amir Michael, Server system lead at Facebook the other week at LinuxCon and I asked him.

According to Michael, Facebook Linux was based originally on CentOS 5.2. Facebook uses one image that is placed on every server that they have.

"It now probably looks nothing like what we started with, being based originally on CentOS 5.2," Michael said. "The kernel itself is fairly recent and we have a few modifications that we do to it, but for the most part it's based entirely on the mainstream Linux kernel."

So Facebook doesn't get its Linux from a big Linux vendor, like Red Hat…but wait there is another piece to this puzzle.

Michael also told me in passing, the Facebook gets its stuff certified by Red Hat Labs. When I pressed him on that point, he said that Facebook gets its hardware (Open Compute Platform) certified by Red Hat. That means that Facebook's infrastructure while not actually bona fide Red Hat (CentOS is pretty close…), is partially certified for Red Hat's flavors of Linux.

I'm not sure that I got the whole story on Facebook and Red Hat, but I'm not surprised that they run their own modified version of an operating system.

Sean Michael Kerner is a senior editor at InternetNews.com, the news service of the IT Business Edge Network, the network for technology professionals Follow him on Twitter @TechJournalist.