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63b03c0b28
Reformat fstab options description. Now they are easier to read and show up in systemd.directives(7). Use a single sublist for both /etc/fstab and /etc/crypttab options. Many of them can be used in both places. crypttab(5) is updated to use the same docbook elements, so formatting is uniform.
389 lines
20 KiB
XML
389 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='fstab-options'>
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<varlistentry>
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<term><option>discard</option></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><option>cipher=</option></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><option>hash=</option></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><option>keyfile-offset=</option></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><option>keyfile-size=</option></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><option>key-slot=</option></term>
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<listitem><para>Specifies the key slot to
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compare the passphrase or key against.
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If the key slot does not match the given
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passphrase or key, but another would, the
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setup of the device will fail regardless.
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This option implies <option>luks</option>. See
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<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values. The default is to try
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all key slots in sequential order.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>luks</option></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: <option>cipher=</option>,
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<option>hash=</option>,
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<option>size=</option>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>noauto</option></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><option>nofail</option></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><option>plain</option></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><option>read-only</option></term><term><option>readonly</option></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><option>size=</option></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><option>swap</option></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 <option>plain</option>.</para>
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<para>WARNING: Using the <option>swap</option>
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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><option>tcrypt</option></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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<option>cipher=</option>,
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<option>hash=</option>,
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<option>keyfile-offset=</option>,
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<option>keyfile-size=</option>,
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<option>size=</option>.</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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<option>tcrypt-keyfile=</option> 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><option>tcrypt-hidden</option></term>
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<listitem><para>Use the hidden TrueCrypt volume.
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This option implies <option>tcrypt</option>.</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><option>tcrypt-keyfile=</option></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 <option>tcrypt</option> 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 <option>tcrypt</option>
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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><option>tcrypt-system</option></term>
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<listitem><para>Use TrueCrypt in system
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encryption mode. This option implies
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<option>tcrypt</option>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>timeout=</option></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><option>tmp</option></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 <option>plain</option>.</para>
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<para>WARNING: Using the <option>tmp</option>
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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><option>tries=</option></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><option>verify</option></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 /dev/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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