zerofree
Zero free blocks from ext2, ext3 and ext4 file-systems
Platforms: Linux · Last verified September 6, 2026
Zerofree finds the unallocated blocks with non-zero value content in an ext2, ext3 or ext4 file-system and fills them with zeroes (zerofree can also work with another value than zero). This is mostly useful if the device on which this file-system resides is a disk image. In this case, depending on the type of disk image, a secondary utility may be able to reduce the size of the disk image after zerofree has been run. Zerofree requires the file-system to be unmounted or mounted read-only.
Only use this tool against systems you own or are explicitly authorized to test — see the disclaimer.
Getting started
See the official Kali tool page and upstream homepage linked above for installation and usage details.
