For some reason ubuntu, by default, does not use the entire disk anymore. This is annoying when you install it on a VM with low diskspace.
neurotechnics.com has a great blog post about this topic. Here is the very short version:
1. Check the size of the current volume: df -hT /dev/mapper/ubuntu--vg-ubuntu--lv 2. Check that a resize is possible (-t parameter): sudo lvresize -tvl +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv 3. Resize: sudo lvresize -vl +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv 4. Resize the filesystem: sudo resize2fs -p /dev/mapper/ubuntu--vg-ubuntu--lv 5. Check the size of the volume: df -hT /dev/mapper/ubuntu--vg-ubuntu--lv