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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.

The usual way to achieve the same result (zeroing the unused blocks) is to run “dd” to create a file full of zeroes that takes up the entire free space on the drive, and then delete this file. This has many disadvantages, which zerofree alleviates:

  • it is slow;
  • it makes the disk image (temporarily) grow to its maximal extent;
  • it (temporarily) uses all free space on the disk, so other concurrent write actions may fail.

Zerofree has been written to be run from GNU/Linux systems installed as guest OSes inside a virtual machine. If this is not your case, you almost certainly don’t need this package. (One other use case would be to erase sensitive data a little bit more securely than with a simple “rm”).

Installed size: 25 KB
How to install: sudo apt install zerofree

  • libc6
  • libext2fs2

Zero free blocks from ext2, ext3 and ext4 file-systems

root@kali:~# zerofree -h
zerofree: invalid option -- 'h'
usage: zerofree [-n] [-v] [-f fillval] filesystem

Updated on: 2022-Aug-05