Compacting VirtualBox Disk Images - Linux Guests

1. Start the Linux virtual machine;
2. Clean the free space on the disk of the Linux virtual machine;

   dd if=/dev/zero of=zerofillfile bs=1M

   • if= specifies the input file;
   • /dev/zero indicates a bit-stream of zeros
   • of= specifies the output file
   • zerofillfile name of the file containing the bit-stream of zeros
   • bs= indicates the block size
   • 1M indicates that the block size will be 1 megabyte

   rm zerofillfile

3. Shutdown the Linux virtual machine;
4. Use the VirtualBox VBoxManage utility to compact the Linux guest image.

Ref: Compacting VirtualBox Disk Images - Linux Guests