Shrink VirtualBox Image

Although we assign 40/50gb hdd space to VM, not all of it is used.
After using VM for sometime, you may find vdi is constantly increasing & may need to shrink it.

To Shrink vdi size.
Linux

dd if=/dev/zero of=/testfile
rm -rf /testfile

Windows

sdelete -c

You can download sdelete from

Run following command to shrink image
Linux

VBoxManage modifyvdi hdd.vdi --compact

Windows

VBoxManage.exe  modifyvdi hdd.vdi --compact