Provided by: zerofree_1.0.1-2ubuntu1_i386 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)