ZEROFREE(8)ZEROFREE(8)NAMEzerofree — zero free blocks from ext2/3 file-systems
SYNOPSISzerofree [-n] [-v] filesystem
DESCRIPTIONzerofree 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 con‐
current 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.source‐
forge.net> for the Debian system (but may be used by others). Permis‐
sion 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)
