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       zerofree — zero free blocks from ext2/3 file-systems


       zerofree [-n]  [-v]  filesystem


       zerofree  finds  the  unallocated, non-zeroed blocks in an ext2 or ext3
       filesystem (e.g. /dev/hda1) and fills them with zeroes. This is  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

       The usual way to achieve  the  same  result  (zeroing  the  unallocated
       blocks)  is to run dd (1) 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.

       filesystem  has  to  be  unmounted or mounted read-only for zerofree to
       work. It will exit with an error message if the filesystem  is  mounted
       writable.  To  remount  the  root  file-system  readonly, you can first
       switch to single user runlevel (telinit 1) then use mount -o remount,ro

       zerofree has been written to be run from GNU/Linux systems installed as
       guest OSes inside a virtual machine. It may however be useful in  other


       -n        Perform a dry run  (do not modify the file-system);

       -v        Be verbose.


       dd (1).


       This     manual     page     was    written    by    Thibaut    Paumard
       <> for the Debian system (but may be  used
       by  others).   Permission  is granted to copy, distribute and/or modify
       this document under the  terms  of  the  GNU  General  Public  License,
       Version  2  or  any  later  version  published  by  the  Free  Software

       On Debian systems, the complete text of the GNU General Public  License
       can be found in /usr/share/common-licenses/GPL-2.