Provided by: zerofree_1.0.1-2ubuntu1_amd64 bug

NAME

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

SYNOPSIS

       zerofree [-n]  [-v]  filesystem

DESCRIPTION

       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
       run.

       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 filesystem.

       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 situations.

OPTIONS

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

       -v        Be verbose.

SEE ALSO

       dd (1).

AUTHOR

       This manual page was written by Thibaut Paumard  <paumard@users.sourceforge.net>  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 Foundation.

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

                                                                                      ZEROFREE(8)