I run Ubuntu on a
VirtualBox system, where I had reserved somewhat too little diskspace for getting our build system to work there (esp. when you have to build a specific gcc version up-front). While it's no problem to increase the size of the virtualized disk within VirtualBox, the partitioning within this disk, particularly of the root partition (the one that Ubuntu is actually running on), might turn out to be difficult to change on -the-fly. I then found and applied
GParted to assign the additional disk space to the root partition, which - despite a "potential data loss risk" warning - worked like a charm.