path: root/source/a/zerofree/zerofree.sgml

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  <!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>

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