zerofree 1.1.1 Zero non-allocated regions in ext2/ext3/ext4 file systems

Zerofree finds the unallocated blocks with non-zero value content in an ext2, ext3, or ext4 file system and fills them with zeroes (or another value). This is a simple way to make disk images more compressible. Zerofree requires the file system to be unmounted or mounted read-only.