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382 lines
20 KiB
XML
382 lines
20 KiB
XML
<?xml version="1.0"?>
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<!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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This is based on crypttab(5) from Fedora's initscripts package, which in
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turn is based on Debian's version.
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The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
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-->
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<refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP'>
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<refentryinfo>
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<title>crypttab</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Documentation</contrib>
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<firstname>Miloslav</firstname>
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<surname>Trmac</surname>
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<email>mitr@redhat.com</email>
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</author>
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<author>
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<contrib>Documentation</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>crypttab</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>crypttab</refname>
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<refpurpose>Configuration for encrypted block devices</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/etc/crypttab</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The <filename>/etc/crypttab</filename> file
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describes encrypted block devices that are set up
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during system boot.</para>
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<para>Empty lines and lines starting with the <literal>#</literal>
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character are ignored. Each of the remaining lines
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describes one encrypted block device, fields on the
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line are delimited by white space. The first two
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fields are mandatory, the remaining two are
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optional.</para>
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<para>Setting up encrypted block devices using this file
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supports three encryption modes: LUKS, TrueCrypt and plain.
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See <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for more information about each mode. When no mode is specified
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in the options field and the block device contains a LUKS
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signature, it is opened as a LUKS device; otherwise, it is
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assumed to be in raw dm-crypt (plain mode) format.</para>
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<para>The first field contains the name of the
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resulting encrypted block device; the device is set up
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within <filename>/dev/mapper/</filename>.</para>
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<para>The second field contains a path to the
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underlying block device or file, or a specification of a block
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device via <literal>UUID=</literal> followed by the
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UUID.</para>
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<para>The third field specifies the encryption
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password. If the field is not present or the password
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is set to <literal>none</literal> or <literal>-</literal>,
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the password has to be manually entered during system boot.
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Otherwise, the field is interpreted as a absolute path to
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a file containing the encryption password. For swap encryption,
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<filename>/dev/urandom</filename> or the hardware
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device <filename>/dev/hw_random</filename> can be used
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as the password file; using
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<filename>/dev/random</filename> may prevent boot
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completion if the system does not have enough entropy
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to generate a truly random encryption key.</para>
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<para>The fourth field, if present, is a
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comma-delimited list of options. The following
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options are recognized:</para>
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<variablelist class='crypttab-options'>
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<varlistentry>
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<term><varname>discard</varname></term>
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<listitem><para>Allow discard requests to be
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passed through the encrypted block device. This
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improves performance on SSD storage but has
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security implications.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>cipher=</varname></term>
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<listitem><para>Specifies the cipher to use. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of
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this option. A cipher with unpredictable IV
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values, such as <literal>aes-cbc-essiv:sha256</literal>,
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is recommended.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>hash=</varname></term>
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<listitem><para>Specifies the hash to use for
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password hashing. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of
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this option.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>keyfile-offset=</varname></term>
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<listitem><para>Specifies the number of bytes to
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skip at the start of the key file. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of
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this option.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>keyfile-size=</varname></term>
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<listitem><para>Specifies the maximum number
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of bytes to read from the key file. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of
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this option. This option is ignored in plain
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encryption mode, as the key file size is then
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given by the key size.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>luks</varname></term>
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<listitem><para>Force LUKS mode. When this mode
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is used, the following options are ignored since
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they are provided by the LUKS header on the
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device: <varname>cipher=</varname>,
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<varname>hash=</varname>,
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<varname>size=</varname>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>noauto</varname></term>
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<listitem><para>This device will not be
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automatically unlocked on boot.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>nofail</varname></term>
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<listitem><para>The system will not wait for the
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device to show up and be unlocked at boot, and
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not fail the boot if it does not show up.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>plain</varname></term>
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<listitem><para>Force plain encryption mode.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>read-only</varname></term><term><varname>readonly</varname></term>
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<listitem><para>Set up the encrypted block
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device in read-only mode.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>size=</varname></term>
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<listitem><para>Specifies the key size
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in bits. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of
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this option.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>swap</varname></term>
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<listitem><para>The encrypted block device will
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be used as a swap device, and will be formatted
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accordingly after setting up the encrypted
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block device, with
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<citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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This option implies <varname>plain</varname>.</para>
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<para>WARNING: Using the <varname>swap</varname>
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option will destroy the contents of the named
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partition during every boot, so make sure the
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underlying block device is specified correctly.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>tcrypt</varname></term>
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<listitem><para>Use TrueCrypt encryption mode.
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When this mode is used, the following options are
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ignored since they are provided by the TrueCrypt
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header on the device or do not apply:
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<varname>cipher=</varname>,
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<varname>hash=</varname>,
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<varname>keyfile-offset=</varname>,
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<varname>keyfile-size=</varname>,
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<varname>size=</varname>.</para>
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<para>When this mode is used, the passphrase is
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read from the key file given in the third field.
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Only the first line of this file is read,
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excluding the new line character.</para>
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<para>Note that the TrueCrypt format uses both
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passphrase and key files to derive a password
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for the volume. Therefore, the passphrase and
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all key files need to be provided. Use
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<varname>tcrypt-keyfile=</varname> to provide
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the absolute path to all key files. When using
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an empty passphrase in combination with one or
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more key files, use <literal>/dev/null</literal>
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as the password file in the third field.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>tcrypt-hidden</varname></term>
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<listitem><para>Use the hidden TrueCrypt volume.
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This implies <varname>tcrypt</varname>.</para>
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<para>This will map the hidden volume that is
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inside of the volume provided in the second
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field. Please note that there is no protection
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for the hidden volume if the outer volume is
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mounted instead. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for more information on this limitation.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>tcrypt-keyfile=</varname></term>
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<listitem><para>Specifies the absolute path to a
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key file to use for a TrueCrypt volume. This
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implies <varname>tcrypt</varname> and can be
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used more than once to provide several key
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files.</para>
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<para>See the entry for <varname>tcrypt</varname>
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on the behavior of the passphrase and key files
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when using TrueCrypt encryption mode.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>tcrypt-system</varname></term>
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<listitem><para>Use TrueCrypt in system
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encryption mode. This implies
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<varname>tcrypt</varname>.</para>
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<para>Please note that when using this mode, the
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whole device needs to be given in the second
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field instead of the partition. For example: if
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<literal>/dev/sda2</literal> is the system
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encrypted TrueCrypt patition, <literal>/dev/sda</literal>
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has to be given.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>timeout=</varname></term>
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<listitem><para>Specifies the timeout for
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querying for a password. If no unit is
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specified, seconds is used. Supported units are
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s, ms, us, min, h, d. A timeout of 0 waits
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indefinitely (which is the default).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>tmp</varname></term>
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<listitem><para>The encrypted block device will
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be prepared for using it as <filename>/tmp</filename>;
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it will be formatted using
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<citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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This option implies <varname>plain</varname>.</para>
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<para>WARNING: Using the <varname>tmp</varname>
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option will destroy the contents of the named
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partition during every boot, so make sure the
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underlying block device is specified correctly.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>tries=</varname></term>
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<listitem><para>Specifies the maximum number of
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times the user is queried for a password.
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The default is 3. If set to 0, the user is
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queried for a password indefinitely.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>verify</varname></term>
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<listitem><para> If the encryption password is
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read from console, it has to be entered twice to
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prevent typos.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>At early boot and when the system manager
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configuration is reloaded, this file is translated into
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native systemd units
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by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<example>
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<title>/etc/crypttab example</title>
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<para>Set up four encrypted block devices. One using
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LUKS for normal storage, another one for usage as a swap
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device and two TrueCrypt volumes.</para>
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<programlisting>luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
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swap /dev/sda7 /dev/urandom swap
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truecrypt /dev/sda2 /etc/container_password tcrypt
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hidden /mnt/tc_hidden /null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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