mirror of
https://github.com/Ponce/slackbuilds
synced 2024-10-05 23:07:14 +02:00
92 lines
3.2 KiB
Groff
92 lines
3.2 KiB
Groff
.TH "ZEROFREE" "8"
|
|
.SH "NAME"
|
|
zerofree \(em zero free blocks from ext2, ext3 and ext4 file-systems
|
|
.SH "SYNOPSIS"
|
|
.PP
|
|
\fBzerofree\fR [\fB-n\fP] [\fB-v\fP] [\fB-f fillval\fP] \fIfilesystem\fR
|
|
.SH "DESCRIPTION"
|
|
.PP
|
|
\fBzerofree\fR finds the unallocated,
|
|
blocks with non-zero value content in an ext2, ext3 or ext4
|
|
\fIfilesystem\fR (e.g. /dev/hda1) and
|
|
fills them with zeroes (or another octet of your choice).
|
|
|
|
|
|
.PP
|
|
Filling unused areas with zeroes 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.
|
|
|
|
.PP
|
|
Filling unused areas may also be useful with solid-state
|
|
drives (SSDs). On some SSDs, filling blocks with ones (0xFF)
|
|
is reported to trigger Flash block erasure by the firmware,
|
|
possibly giving a write performance increase.
|
|
|
|
.PP
|
|
The usual way to achieve the same result (zeroing the
|
|
unallocated blocks) is to run \fBdd\fR (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:
|
|
.IP " \(bu" 6
|
|
it is slow;
|
|
.IP " \(bu" 6
|
|
it makes the disk image (temporarily) grow to its maximal
|
|
extent;
|
|
.IP " \(bu" 6
|
|
it (temporarily) uses all free space on the disk, so other
|
|
concurrent write actions may fail.
|
|
|
|
.PP
|
|
\fIfilesystem\fR has to be unmounted or
|
|
mounted read-only for \fBzerofree\fR to work. It
|
|
will exit with an error message if the
|
|
\fIfilesystem\fR is mounted writable. To
|
|
remount the root file-system readonly, you can first switch to
|
|
single user runlevel (\fBtelinit 1\fR) then use
|
|
\fBmount \-o remount,ro
|
|
\fIfilesystem\fR\fR.
|
|
|
|
.PP
|
|
\fBzerofree\fR has been written to be run
|
|
from GNU/Linux systems installed as guest OSes inside a virtual
|
|
machine. In this case, it is typically run from within the guest
|
|
system, and a utility is then run from the host system to shrink
|
|
disk image (\fBVBoxManage modifyhd \-\-compact\fR,
|
|
provided with virtualbox, is able to do that for some disk image
|
|
formats).
|
|
|
|
.PP
|
|
It may however be useful in other situations: for instance
|
|
it can be used to make it more difficult to retrieve deleted
|
|
data. Beware that securely deleting sensitive data is not in
|
|
general an easy task and usually requires writing several times
|
|
on the deleted blocks.
|
|
|
|
.SH "OPTIONS"
|
|
.IP "\fB-n\fP " 10
|
|
Perform a dry run (do not modify the file-system);
|
|
.IP "\fB-v\fP " 10
|
|
Be verbose;
|
|
.IP "\fB-f value\fP " 10
|
|
Specify the octet value to fill empty blocks with (defaults to
|
|
0). Argument must be within the range 0 to 255.
|
|
.SH "SEE ALSO"
|
|
.PP
|
|
dd (1).
|
|
.SH "AUTHOR"
|
|
.PP
|
|
This manual page was written by Thibaut Paumard <paumard@users.sourceforge.net> for
|
|
the \fBDebian\fP 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.
|
|
|
|
.PP
|
|
On Debian systems, the complete text of the GNU General Public
|
|
License can be found in /usr/share/common-licenses/GPL-2.
|
|
|
|
.\" created by instant / docbook-to-man, Mon 31 Mar 2014, 15:41
|