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<!doctype refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN" [
<!-- Process this file with docbook-to-man to generate an nroff manual
page: `docbook-to-man manpage.sgml > manpage.1'. You may view
the manual page with: `docbook-to-man manpage.sgml | nroff -man |
less'.
-->
<!ENTITY dhfirstname "<firstname>Thibaut</firstname>">
<!ENTITY dhsurname "<surname>Paumard</surname>">
<!-- Please adjust the date whenever revising the manpage. -->
<!ENTITY dhdate "<date>February 6, 2008</date>">
<!ENTITY dhsection "<manvolnum>8</manvolnum>">
<!ENTITY dhemail "<email><paumard@users.sourceforge.net></email>">
<!ENTITY dhusername "Thibaut Paumard">
<!ENTITY dhucpackage "<refentrytitle>ZEROFREE</refentrytitle>">
<!ENTITY dhpackage "zerofree">
<!ENTITY debian "<productname>Debian</productname>">
<!ENTITY gnu "<acronym>GNU</acronym>">
<!ENTITY gpl "&gnu; <acronym>GPL</acronym>">
]>
<refentry>
<refentryinfo>
<address>
&dhemail;
</address>
<author>
&dhfirstname;
&dhsurname;
</author>
<copyright>
<year>2003</year>
<holder>&dhusername;</holder>
</copyright>
&dhdate;
</refentryinfo>
<refmeta>
&dhucpackage;
&dhsection;
</refmeta>
<refnamediv>
<refname>&dhpackage;</refname>
<refpurpose>zero free blocks from ext2/3/4 file-systems</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>&dhpackage;</command>
<arg><option>-n</option></arg>
<arg><option>-v</option></arg>
<arg choice=req><replaceable>filesystem</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>DESCRIPTION</title>
<para><command>&dhpackage;</command> finds the unallocated,
non-zeroed blocks in an ext2, ext3, or ext4
<replaceable>filesystem</replaceable> (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.</para>
<para>The usual way to achieve the same result (zeroing the
unallocated blocks) is to run <command>dd</command> (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:</para>
<itemizedlist>
<listitem><para>it is slow;</para></listitem>
<listitem><para>it makes the disk image (temporarily) grow to its maximal
extent;</para></listitem>
<listitem><para>it (temporarily) uses all free space on the disk, so other
concurrent write actions may fail.</para></listitem>
</itemizedlist>
<para><replaceable>filesystem</replaceable> has to be unmounted or
mounted read-only for <command>&dhpackage;</command> to work. It
will exit with an error message if the
<replaceable>filesystem</replaceable> is mounted writable. To
remount the root file-system readonly, you can first switch to
single user runlevel (<command>telinit 1</command>) then use
<command>mount -o remount,ro
<replaceable>filesystem</replaceable></command>.</para>
<para><command>&dhpackage;</command> 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.</para>
</refsect1>
<refsect1>
<title>OPTIONS</title>
<variablelist>
<varlistentry>
<term><option>-n</option>
</term>
<listitem>
<para>Perform a dry run (do not modify the file-system);</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-v</option>
</term>
<listitem>
<para>Be verbose.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>SEE ALSO</title>
<para>dd (1).</para>
</refsect1>
<refsect1>
<title>AUTHOR</title>
<para>This manual page was written by &dhusername; &dhemail; 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.
</para>
<para>
On Debian systems, the complete text of the GNU General Public
License can be found in /usr/share/common-licenses/GPL-2.
</para>
</refsect1>
</refentry>
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