Here's the brief description (from Open Platform):
Installing an “Other OS" on PLAYSTATION®3 requires two files. One is the “Other OS Installer” distributed by Sony Computer Entertainment Inc. (which is called installer hereafter), and the other is the “Other OS boot loader” (called boot loader hereafter) provided by the third party.
The installer installs the boot loader of an "Other OS" on a boot‐loader‐dedicated storage area of PLAYSTATION®3. Once the boot loader of an "Other OS" has been successfully installed, it automatically starts up instead of the PLAYSTATION®3’s system software at every power on by selecting it as”Default System”in the menu of the PLAYSTATION®3’s system software.
The installer installs only the boot loader of an "Other OS". It is assumed that any further installations, such as the installation of "Other OS" files on the built-in hard disk of PLAYSTATION®3, are performed when the installed boot loader starts up. For more details, please contact the provider of the boot loader you are using.
If you want to do this, please read the manual first.
This is not the first time GNU/Linux OS can be installed and running on gaming console. Nintendo DS was the other example.