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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>&lt;paumard@users.sourceforge.net&gt;</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>
+
+<!-- Keep this comment at the end of the file
+Local variables:
+mode: sgml
+sgml-omittag:t
+sgml-shorttag:t
+sgml-minimize-attributes:nil
+sgml-always-quote-attributes:t
+sgml-indent-step:2
+sgml-indent-data:t
+sgml-parent-document:nil
+sgml-default-dtd-file:nil
+sgml-exposed-tags:nil
+sgml-local-catalogs:nil
+sgml-local-ecat-files:nil
+End:
+-->
+
+