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Is there a Linux Program that will overwrite free disk space in a secure manner?
Zerofree finds the unallocated blocks with non-zero value content inan ext2, ext3 or ext4 file-system and fills them with zeroes(zerofree can also work with another value than zero). This is mostlyuseful if the device on which this file-system resides is a diskimage. In this case, depending on the type of disk image, a secondaryutility may be able to reduce the size of the disk image afterzerofree has been run. Zerofree requires the file-system to beunmounted or mounted read-only.The usual way to achieve the same result (zeroing the unusedblocks) is to run "dd" do create a file full of zeroes that takes upthe entire free space on the drive, and then delete this file. Thishas 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 installedas guest OSes inside a virtual machine. If this is not your case, youalmost certainly don't need this package. (One other use case wouldbe to erase sensitive data a little bit more securely than with asimple "rm").
Gutmann method based tools for securely wiping data from files, freedisk space, swap and memory: srm, sfill, sswap and sdmem.