The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
-->
-<refentry id="crypttab">
+<refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP'>
<refentryinfo>
<title>crypttab</title>
describes encrypted block devices that are set up
during system boot.</para>
- <para>Empty lines and lines starting with the #
+ <para>Empty lines and lines starting with the <literal>#</literal>
character are ignored. Each of the remaining lines
describes one encrypted block device, fields on the
line are delimited by white space. The first two
fields are mandatory, the remaining two are
optional.</para>
+ <para>Setting up encrypted block devices using this file
+ supports three encryption modes: LUKS, TrueCrypt and plain.
+ See <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for more information about each mode. When no mode is specified
+ in the options field and the block device contains a LUKS
+ signature, it is opened as a LUKS device; otherwise, it is
+ assumed to be in raw dm-crypt (plain mode) format.</para>
+
<para>The first field contains the name of the
resulting encrypted block device; the device is set up
within <filename>/dev/mapper/</filename>.</para>
<para>The second field contains a path to the
- underlying block device, or a specification of a block
+ underlying block device or file, or a specification of a block
device via <literal>UUID=</literal> followed by the
- UUID. If the block device contains a LUKS signature,
- it is opened as a LUKS encrypted partition; otherwise
- it is assumed to be a raw dm-crypt partition.</para>
+ UUID.</para>
<para>The third field specifies the encryption
password. If the field is not present or the password
- is set to none, the password has to be manually
- entered during system boot. Otherwise the field is
- interpreted as a path to a file containing the
- encryption password. For swap encryption
+ is set to <literal>none</literal> or <literal>-</literal>,
+ the password has to be manually entered during system boot.
+ Otherwise, the field is interpreted as a absolute path to
+ a file containing the encryption password. For swap encryption,
<filename>/dev/urandom</filename> or the hardware
device <filename>/dev/hw_random</filename> can be used
as the password file; using
comma-delimited list of options. The following
options are recognized:</para>
- <variablelist>
+ <variablelist class='crypttab-options'>
+
+ <varlistentry>
+ <term><varname>discard</varname></term>
+
+ <listitem><para>Allow discard requests to be
+ passed through the encrypted block device. This
+ improves performance on SSD storage but has
+ security implications.</para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>cipher=</varname></term>
- <listitem><para>Specifies the cipher
- to use; see
+ <listitem><para>Specifies the cipher to use. See
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- for possible values and the default
- value of this option. A cipher with
- unpredictable IV values, such as
- <literal>aes-cbc-essiv:sha256</literal>,
- is recommended. </para></listitem>
+ for possible values and the default value of
+ this option. A cipher with unpredictable IV
+ values, such as <literal>aes-cbc-essiv:sha256</literal>,
+ is recommended.</para></listitem>
</varlistentry>
-
<varlistentry>
- <term><varname>size=</varname></term>
+ <term><varname>hash=</varname></term>
- <listitem><para>Specifies the key size
- in bits; see
+ <listitem><para>Specifies the hash to use for
+ password hashing. See
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- for possible values and the default
- value of this
- option. </para></listitem>
+ for possible values and the default value of
+ this option.</para></listitem>
</varlistentry>
-
<varlistentry>
<term><varname>keyfile-offset=</varname></term>
- <listitem><para>Specifies the number
- of bytes to skip at the start of
- the keyfile; see
+ <listitem><para>Specifies the number of bytes to
+ skip at the start of the key file. See
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- for possible values and the default
- value of this option.</para></listitem>
+ for possible values and the default value of
+ this option.</para></listitem>
</varlistentry>
-
<varlistentry>
- <term><varname>hash=</varname></term>
+ <term><varname>keyfile-size=</varname></term>
- <listitem><para>Specifies the hash to
- use for password hashing; see
- <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> for possible values and
- the default value of this
- option. </para></listitem>
+ <listitem><para>Specifies the maximum number
+ of bytes to read from the key file. See
+ <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of
+ this option. This option is ignored in plain
+ encryption mode, as the key file size is then
+ given by the key size.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>tries=</varname></term>
+ <term><varname>luks</varname></term>
- <listitem><para>Specifies the maximum
- number of times the user is queried
- for a password.</para></listitem>
+ <listitem><para>Force LUKS mode. When this mode
+ is used, the following options are ignored since
+ they are provided by the LUKS header on the
+ device: <varname>cipher=</varname>,
+ <varname>hash=</varname>,
+ <varname>size=</varname>.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>verify</varname></term>
+ <term><varname>noauto</varname></term>
- <listitem><para> If the the encryption
- password is read from console, it has
- to be entered twice (to prevent
- typos). </para></listitem>
+ <listitem><para>This device will not be
+ automatically unlocked on boot.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>read-only</varname></term>
+ <term><varname>nofail</varname></term>
- <listitem><para>Set up the encrypted
- block device in read-only
- mode.</para></listitem>
+ <listitem><para>The system will not wait for the
+ device to show up and be unlocked at boot, and
+ not fail the boot if it does not show up.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>allow-discards</varname></term>
-
- <listitem><para>Allow discard requests
- to be passed through the encrypted
- block device. This improves
- performance on SSD storage but has
- security
- implications.</para></listitem>
+ <term><varname>plain</varname></term>
+
+ <listitem><para>Force plain encryption mode.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>luks</varname></term>
+ <term><varname>read-only</varname></term><term><varname>readonly</varname></term>
- <listitem><para>Force LUKS mode.</para></listitem>
+ <listitem><para>Set up the encrypted block
+ device in read-only mode.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>plain</varname></term>
+ <term><varname>size=</varname></term>
- <listitem><para>Force plain encryption
- mode.</para></listitem>
+ <listitem><para>Specifies the key size
+ in bits. See
+ <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of
+ this option.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>timeout=</varname></term>
+ <term><varname>swap</varname></term>
- <listitem><para>Specify the timeout
- for querying for a password. If not
- unit is specified in
- seconds. Supported units are s, ms,
- us, min, h, d.</para></listitem>
+ <listitem><para>The encrypted block device will
+ be used as a swap device, and will be formatted
+ accordingly after setting up the encrypted
+ block device, with
+ <citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ This option implies <varname>plain</varname>.</para>
+
+ <para>WARNING: Using the <varname>swap</varname>
+ option will destroy the contents of the named
+ partition during every boot, so make sure the
+ underlying block device is specified correctly.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>noauto</varname></term>
+ <term><varname>tcrypt</varname></term>
+
+ <listitem><para>Use TrueCrypt encryption mode.
+ When this mode is used, the following options are
+ ignored since they are provided by the TrueCrypt
+ header on the device or do not apply:
+ <varname>cipher=</varname>,
+ <varname>hash=</varname>,
+ <varname>keyfile-offset=</varname>,
+ <varname>keyfile-size=</varname>,
+ <varname>size=</varname>.</para>
+
+ <para>When this mode is used, the passphrase is
+ read from the key file given in the third field.
+ Only the first line of this file is read,
+ excluding the new line character.</para>
+
+ <para>Note that the TrueCrypt format uses both
+ passphrase and key files to derive a password
+ for the volume. Therefore, the passphrase and
+ all key files need to be provided. Use
+ <varname>tcrypt-keyfile=</varname> to provide
+ the absolute path to all key files. When using
+ an empty passphrase in combination with one or
+ more key files, use <literal>/dev/null</literal>
+ as the password file in the third field.</para></listitem>
+ </varlistentry>
- <listitem><para> This device will not
- be automatically unlocked on
- boot. </para></listitem>
+ <varlistentry>
+ <term><varname>tcrypt-hidden</varname></term>
+
+ <listitem><para>Use the hidden TrueCrypt volume.
+ This implies <varname>tcrypt</varname>.</para>
+
+ <para>This will map the hidden volume that is
+ inside of the volume provided in the second
+ field. Please note that there is no protection
+ for the hidden volume if the outer volume is
+ mounted instead. See
+ <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for more information on this limitation.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>nofail</varname></term>
+ <term><varname>tcrypt-keyfile=</varname></term>
+
+ <listitem><para>Specifies the absolute path to a
+ key file to use for a TrueCrypt volume. This
+ implies <varname>tcrypt</varname> and can be
+ used more than once to provide several key
+ files.</para>
- <listitem><para>The system will not
- wait for the device to show up and be
- unlocked at boot, and not fail the
- boot if it doesn't show
- up.</para></listitem>
+ <para>See the entry for <varname>tcrypt</varname>
+ on the behavior of the passphrase and key files
+ when using TrueCrypt encryption mode.</para></listitem>
</varlistentry>
<varlistentry>
- <term><varname>swap</varname></term>
+ <term><varname>tcrypt-system</varname></term>
+
+ <listitem><para>Use TrueCrypt in system
+ encryption mode. This implies
+ <varname>tcrypt</varname>.</para>
+
+ <para>Please note that when using this mode, the
+ whole device needs to be given in the second
+ field instead of the partition. For example: if
+ <literal>/dev/sda2</literal> is the system
+ encrypted TrueCrypt patition, <literal>/dev/sda</literal>
+ has to be given.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>timeout=</varname></term>
- <listitem><para> The encrypted block
- device will be used as a swap
- partition, and will be formatted as a
- swap partition after setting up the
- encrypted block device, with
- <citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
-
- <para>WARNING: Using the
- <varname>swap</varname> option will
- destroy the contents of the named
- partition during every boot, so make
- sure the underlying block device is
- specified
- correctly. </para></listitem>
+ <listitem><para>Specifies the timeout for
+ querying for a password. If no unit is
+ specified, seconds is used. Supported units are
+ s, ms, us, min, h, d. A timeout of 0 waits
+ indefinitely (which is the default).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>tmp</varname></term>
- <listitem><para>The encrypted block
- device will be prepared for using it
- as <filename>/tmp</filename>
- partition: it will be formatted using
- <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
-
- <para>WARNING: Using the
- <varname>tmp</varname> option will
- destroy the contents of the named
- partition during every boot, so make
- sure the underlying block device is
- specified
- correctly. </para></listitem>
+ <listitem><para>The encrypted block device will
+ be prepared for using it as <filename>/tmp</filename>;
+ it will be formatted using
+ <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ This option implies <varname>plain</varname>.</para>
+
+ <para>WARNING: Using the <varname>tmp</varname>
+ option will destroy the contents of the named
+ partition during every boot, so make sure the
+ underlying block device is specified correctly.</para></listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><varname>tries=</varname></term>
+
+ <listitem><para>Specifies the maximum number of
+ times the user is queried for a password.
+ The default is 3. If set to 0, the user is
+ queried for a password indefinitely.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>verify</varname></term>
+
+ <listitem><para> If the encryption password is
+ read from console, it has to be entered twice to
+ prevent typos.</para></listitem>
+ </varlistentry>
+
</variablelist>
<para>At early boot and when the system manager
- configuration is reloaded this file is translated into
+ configuration is reloaded, this file is translated into
native systemd units
by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</refsect1>
<title>Example</title>
<example>
<title>/etc/crypttab example</title>
- <para>Set up two encrypted block devices with
- LUKS: one normal one for storage, and another
- one for usage as swap device.</para>
-
- <programlisting>luks-2505567a-9e27-4efe-a4d5-15ad146c258b UUID=2505567a-9e27-4efe-a4d5-15ad146c258b - timeout=0
-swap /dev/sda7 /dev/urandom swap</programlisting>
+ <para>Set up four encrypted block devices. One using
+ LUKS for normal storage, another one for usage as a swap
+ device and two TrueCrypt volumes.</para>
+
+ <programlisting>luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
+swap /dev/sda7 /dev/urandom swap
+truecrypt /dev/sda2 /etc/container_password tcrypt
+hidden /mnt/tc_hidden /null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
</example>
</refsect1>
~ianmdlvl / elogind.git / blobdiff