We have some details about the development of the Playstation 4 OS.
The Operating System is called “Orbis OS”. It is a modified version of FreeBSD 9.0.
We aren’t sure if this will bring again the “Other OS” functions to Playstation 4 (remember that this option enabled Playstation 3 to install other OS in the console like linux or windows).
When you boot up a second-gen development kit, you will be prompted with several options, as you can see in the next captures:
More options appear when you choose startup settings:
As you can imagine you have either a console mode or a graphic mode (the one you will see in a retail Playstation 4).
Here you can see some images of the console mode and some of the files/directories in the devkit:
Honestly I don't know if there's anything significant in these screenshots :/
http://www.vgleaks.com/some-details-about-playstation-4-os-development/