If we're talking about bare metal and desktops/laptops then this might be the next impossible solution on a given Linux/Unix machine, but there are a few workarounds and the best one i feel is supposed to use Gparted tool. Now there are a few hiccups here and there. This tool may not permit to perform the above task. Here is a neat explanation below from one of the forums out there… gparted may not allow you to resize the mounted & active root / partition when you are logged into Ubuntu (i.e. mounted /). There are many solutions to resize the root partition depending on your knowledge and experience.