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<refentry id="file.crypttab">

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             xpointer="xpointer(/refentry/refentryinfo)"
             xmlns:xi="http://www.w3.org/2001/XInclude"/>

 <refmeta>
  <refentrytitle>crypttab</refentrytitle>
  <manvolnum>5</manvolnum>
  <xi:include href="variables.xml"
              xpointer="xpointer(/refentry/refmeta/*)"
	      xmlns:xi="http://www.w3.org/2001/XInclude"/>
 </refmeta>

 <refnamediv>
  <refname>crypttab</refname>
  <refpurpose>static information about encrypted filesystems</refpurpose>
 </refnamediv>

 <refsect1 id="crypttab.description">
  <title>DESCRIPTION</title>
  <simpara>
   The file <filename>/etc/crypttab</filename> contains descriptive
   information about encrypted filesystems. <filename>crypttab</filename>
   is only read by programs (e.g.
   <command moreinfo="refentry">cryptdisks_start</command> and
   <command moreinfo="refentry">cryptdisks_stop</command>),
   and not written; it is the duty of the system
   administrator to properly create and maintain this file. Each filesystem is
   described on a separate line; fields on each line are separated by tabs or
   spaces. Lines starting with <quote>#</quote> are comments, empty lines are 
   ignored. The order of records in <filename>crypttab</filename> is important
   because the init scripts sequentially iterate through 
   <filename>crypttab</filename> doing their thing.
  </simpara>
  <simpara>
   The first field, <emphasis>target</emphasis>, describes the mapped
   device name. It must be a plain filename without any directory components.
   A mapped device which encrypts/decrypts data to/from the <emphasis>source
   device</emphasis> will be created at
   <filename class="devicefile">/dev/mapper/target</filename> by
   <command moreinfo="refentry">cryptsetup</command>.
  </simpara>
  <simpara>
   The second field, <emphasis>source device</emphasis>, describes either the
   block special device or file (which will be automatically mounted as a loop
   device) that should hold the encrypted data.
  </simpara>
  <simpara>
   The third field, <emphasis>key file</emphasis>, describes the file to use
   as a key for decrypting the data of the <emphasis>source device</emphasis>.
   Note that the <emphasis>entire</emphasis> key file will be used as the
   passphase; the passphase must <emphasis>not</emphasis> be
   followed by a newline character.
  </simpara>
  <simpara>
   It can also be a device name (e.g.
   <filename class="devicefile">/dev/urandom</filename>), note however that
   LUKS requires a persistent key and therefore does <emphasis>not</emphasis>
   support random data keys.
  </simpara>
  <simpara>
   If the <emphasis>key file</emphasis> is the string <quote>none</quote>, 
   a passphrase will be read interactively from the console. In this case, the
   options precheck, check, checkargs and tries may be useful.
  </simpara>
  <simpara>
   The fourth field, <emphasis>options</emphasis>, describes the cryptsetup
   options associated with the encryption process. At minimum, the field should
   contain either the string <emphasis>luks</emphasis> or the
   <emphasis>cipher</emphasis>, <emphasis>hash</emphasis> and
   <emphasis>size</emphasis> options.
  </simpara>
  <simpara>
   Options are in the format: <emphasis>key</emphasis>=<emphasis>value</emphasis>
   [,<emphasis>key</emphasis>=<emphasis>value</emphasis> &#8230;]. The
   supported options are described below.
  </simpara>
  <simpara>
   Note that all four fields are mandatory and that a missing field will lead
   to unspecified behaviour.
  </simpara>
 </refsect1>

 <refsect1 id="crypttab.options">
  <title>OPTIONS</title>
  <variablelist>

   <varlistentry>
    <term><emphasis>cipher</emphasis>=&lt;cipher&gt;</term>
    <listitem>
     <simpara>
      Encryption algorithm. See <command>cryptsetup -c</command>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>size</emphasis>=&lt;size&gt;</term>
    <listitem>
     <simpara>
      Encryption key size. See <command>cryptsetup -s</command>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>hash</emphasis>=&lt;hash&gt;</term>
    <listitem>
     <simpara>
      Hash algorithm. See <command>cryptsetup -h</command>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>offset</emphasis>=&lt;offset&gt;</term>
    <listitem>
     <simpara>
      Start offset. Uses <emphasis role="strong">cryptsetup -o</emphasis>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>skip</emphasis>=&lt;skip&gt;</term>
    <listitem>
     <simpara>
      Skip sectors at the beginning. Uses <emphasis role="strong">cryptsetup -p</emphasis>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>verify</emphasis></term>
    <listitem>
     <simpara>
      Verify password. Uses <emphasis role="strong">cryptsetup -y</emphasis>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>readonly</emphasis></term>
    <listitem>
     <simpara>The backing device is read-only (eg: a dvd).</simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>luks</emphasis></term>
    <listitem>
     <simpara>Use device with luks extensions.</simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>swap</emphasis></term>
    <listitem>
     <simpara>
      Run <command moreinfo="refentry">mkswap</command> on the created device.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>tmp</emphasis>=&lt;tmpfs&gt;</term>
    <listitem>
     <simpara>
      Run <command moreinfo="refentry">mkfs</command> with filesystem type
      &lt;tmpfs&gt; on the created device. Default is ext2.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>precheck</emphasis>=&lt;precheck&gt;</term>
    <listitem>
     <simpara>Check the content of the source device by a suitable program; if
      the check fails, the device is not created. If a program is provided as an
      argument, it is run, giving the source device as argument.
      Cryptdisks/cryptroot searches for the given progam in
      <filename class="directory">/lib/cryptsetup/checks/</filename> first, but
      full path to program is supported as well.
     </simpara>
     <simpara>
      Prechecks aren't invoked for LUKS devices, as these are checked with isLUKS
      anyway. Default for plain dm-crypt devices is set in
      <filename>/etc/default/cryptdisks</filename>, or <filename>un_blkid</filename>
      otherwise. Set to <filename>/bin/true</filename> in order to disable
      precheck for plain dm-crypt device.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>check</emphasis>=&lt;check&gt;</term>
    <listitem>
     <simpara>Check the content of the target device by a suitable program; if
      the check fails, the device is removed. If a program is provided as an
      argument, it is run, giving the decrypted volume (target device) as
      first argument, and the value of the checkargs option as second argument.
      Cryptdisks/cryptroot searches for the given program in
      <filename class="directory">/lib/cryptsetup/checks/</filename> first, but
      full path to program is supported as well.
     </simpara>
     <simpara>
      Default is set in <filename>/etc/default/cryptdisks</filename>
      (<filename>blkid</filename>).
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>checkargs</emphasis>=&lt;arguments&gt;</term>
    <listitem>
     <simpara>Give &lt;arguments&gt; as the second argument to the check
      script. See the CHECKSCRIPTS section for more information.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>tries</emphasis>=&lt;num&gt;</term>
    <listitem>
     <simpara>The input of the passphrase is tried &lt;num&gt; times in case
      of failure. If you want to disable retries, pass <quote>tries=1</quote>.
      Default is 3. For the root device, <quote>tries=0</quote> enables
      infinitive retries due to a special case in the initramfs scripts.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>noearly</emphasis></term>
    <listitem>
     <simpara>The cryptsetup init scripts are invoked twice during the boot 
      process - once before lvm, evms, raid, etc. are started and once again
      after that. Sometimes you need to start your encrypted disks in a special
      order. With this option the device is ignored during the first invokation
      of the cryptsetup init scripts.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>noauto</emphasis></term>
    <listitem>
     <simpara>Entirely ignore the device at the boot process. It's still
      possible to map the device manually using cryptdisks_start.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>loud</emphasis></term>
    <listitem>
     <simpara>Be loud. Print warnings if a device does not exist.
     This option overwrites the option <emphasis>quiet</emphasis>.</simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>quiet</emphasis></term>
    <listitem>
     <simpara>Be quiet. Don't print warnings if a device does not exist.
     This option overwrites the option <emphasis>loud</emphasis>.</simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>keyscript</emphasis>=&lt;path&gt;</term>
    <listitem>
     <simpara>
      The executable at the indicated path is executed with the
      <emphasis>key file</emphasis> from the third field of the crypttab as its
      only argument and the output is used as the key. This also works with
      encrypted root filesystems via initramfs if the executable is
      self-contained (i.e. an executable which does not rely on any external
      program which is not present in the initramfs environment).
     </simpara>
     <para>
      All fields of the appropriate crypttab entry are available to the keyscript
      as exported environment variables:
      <variablelist>

       <varlistentry>
        <term>CRYPTTAB_NAME</term>
        <listitem><para>
	 The target name
        </para></listitem>
       </varlistentry>
       <varlistentry>
        <term>CRYPTTAB_SOURCE</term>
        <listitem><para>
	 The source device
        </para></listitem>
       </varlistentry>
       <varlistentry>
        <term>CRYPTTAB_KEY</term>
        <listitem><para>
	 The key file
        </para></listitem>
       </varlistentry>
       <varlistentry>
        <term>CRYPTTAB_OPTIONS</term>
        <listitem><para>
	 A list of exported crypttab options
        </para></listitem>
       </varlistentry>
       <varlistentry>
        <term>CRYPTTAB_OPTION_&lt;option&gt;</term>
        <listitem><para>
	 The value of the appropriate crypttab option, with value set to 'yes'
         in case the option is merely a flag.
        </para></listitem>
       </varlistentry>

      </variablelist>
     </para>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1 id="crypttab.checkscripts">
  <title>CHECKSCRIPTS</title>
  <variablelist>

   <varlistentry>
    <term><emphasis>blkid</emphasis></term>
    <listitem>
     <simpara>Checks for any known filesystem. Supports a filesystem type as
      argument via &lt;checkargs&gt;:
     </simpara>
     <itemizedlist>
      <listitem><para>
       no checkargs - succeeds if any valid filesystem is found on the device.
      </para></listitem>
      <listitem><para>
       "none" - succeeds if no valid filesystem is found on the device.
      </para></listitem>
      <listitem><para>
       "ext3" [or another filesystem type like xfs, swap, crypto_LUKS, ...] -
       succeeds if ext3 filesystem is found on the device.
      </para></listitem>
     </itemizedlist>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>un_blkid</emphasis></term>
    <listitem>
     <simpara>Checks for no known filesystem. Supports a filesystem type as
      argument via &lt;checkargs&gt;:
     </simpara>
     <itemizedlist>
      <listitem><para>
       no checkargs - succeeds if no valid filesystem is found on the device.
      </para></listitem>
      <listitem><para>
       "ext3" [or another filesystem type like xfs, swap, crypto_LUKS, ...] -
       succeeds if no ext3 filesystem is found on the device.
      </para></listitem>
     </itemizedlist>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1 id="crypttab.examples">
  <title>EXAMPLES</title>
  <para>
   <screen>
# Encrypted swap device
cswap /dev/sda6 /dev/urandom swap
    
# Encrypted luks disk with interactive password
cdisk0 /dev/hda1 none luks
    
# Encrypted ext2 disk with interactive password
# - retry 5 times if the check fails
cdisk1 /dev/sda2 none checkargs=ext2,tries=5

# Encrypted disk with interactive password
# - use a nondefault check script
# - no retries
cdisk2 /dev/hdc1 none check=customscript,tries=1

# Encrypted disk with interactive password
# - twofish as the cipher
cdisk3 /dev/sda3 none cipher=twofish
   </screen>
  </para>
 </refsect1>

 <refsect1 id="crypttab.environment">
  <title>ENVIRONMENT</title>
  <variablelist>

   <varlistentry>
    <term><emphasis>CRYPTDISKS_ENABLE</emphasis></term>
    <listitem>
     <simpara>
      Set to <emphasis>yes</emphasis> to run cryptdisks initscripts at startup.
      Set to <emphasis>no</emphasis> to disable cryptdisks initscripts. Default
      is <emphasis>yes</emphasis>.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>CRYPTDISKS_MOUNT</emphasis></term>
    <listitem>
     <simpara>Specifies the mountpoints that are mounted before cryptdisks is
      invoked. Takes mountpoints configured in /etc/fstab as arguments. Separate
      mountpoints by space.
      This is useful for keys on removable devices, such as cdrom, usbstick,
      flashcard, etc. Default is unset.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>CRYPTDISKS_CHECK</emphasis></term>
    <listitem>
     <simpara>Specifies the default checkscript to be run against the target
      device, after cryptdisks has been invoked. The target device is passed as
      the first and only argument to the checkscript. Takes effect if the
      <emphasis>check</emphasis> option is given in crypttab with no value. See
      documentation for <emphasis>check</emphasis> option above for more
      information.
     </simpara>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><emphasis>CRYPTDISKS_PRECHECK</emphasis></term>
    <listitem>
     <simpara>Specifies the default checkscript to be run against the source
      dm-crypt device, before cryptdisks has been invoked. The source device
      is given as the first and only argument to the checkscript. Takes effect
      if the <emphasis>precheck</emphasis> option is given in crypttab with no
      value. See documentation for <emphasis>precheck</emphasis> option above
      for more information.
     </simpara>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1 id="crypttab.see_also">
  <title>SEE ALSO</title>
  <simplelist type="inline">
   <member><command moreinfo="refentry">cryptsetup</command>(8)</member>
   <member><command moreinfo="refentry">cryptdisks_start</command>(8)</member>
   <member><command moreinfo="refentry">cryptdisks_stop</command>(8)</member>
  </simplelist>
 </refsect1>

 <refsect1 id="crypttab.author">
  <title>AUTHOR</title>
  <simpara>
   This manual page was originally written by
   <author>
    <firstname>Bastian</firstname>
    <surname>Kleineidam</surname>
   </author>
   <email>calvin@debian.org</email>
   for the Debian distribution of cryptsetup. It has been further improved by
   <author>
    <firstname>Michael</firstname>
    <surname>Gebetsroither</surname>
   </author>
   <email>michael.geb@gmx.at</email>,
   <author>
    <firstname>Jonas</firstname>
    <surname>Meurer</surname>
   </author>
   <email>jonas@freesources.org</email>
   and
   <author>
    <firstname>David</firstname>
    <surname>Härdeman</surname>
   </author>
   <email>david@hardeman.nu</email>.
  </simpara>
 </refsect1>

</refentry>