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![Lennart Poettering](/assets/img/avatar_default.png)
These lines are generally out-of-date, incomplete and unnecessary. With SPDX and git repository much more accurate and fine grained information about licensing and authorship is available, hence let's drop the per-file copyright notice. Of course, removing copyright lines of others is problematic, hence this commit only removes my own lines and leaves all others untouched. It might be nicer if sooner or later those could go away too, making git the only and accurate source of authorship information.
444 lines
19 KiB
XML
444 lines
19 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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SPDX-License-Identifier: LGPL-2.1+
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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 describes
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encrypted block devices that are set up 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 describes one
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encrypted block device. Fields are delimited by white space.</para>
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<para>Each line is in the form<programlisting><replaceable>name</replaceable> <replaceable>encrypted-device</replaceable> <replaceable>password</replaceable> <replaceable>options</replaceable></programlisting>
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The first two 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 supports
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three encryption modes: LUKS, TrueCrypt and plain. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for more information about each mode. When no mode is specified in
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the options field and the block device contains a LUKS signature,
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it is opened as a LUKS device; otherwise, it is assumed to be in
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raw dm-crypt (plain mode) format.</para>
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<para>The first field contains the name of the resulting encrypted
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block device; the device is set up within
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<filename>/dev/mapper/</filename>.</para>
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<para>The second field contains a path to the underlying block
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device or file, or a specification of a block device via
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<literal>UUID=</literal> followed by the UUID.</para>
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<para>The third field specifies the encryption password. If the
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field is not present or the password is set to
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<literal>none</literal> or <literal>-</literal>, the password has
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to be manually entered during system boot. Otherwise, the field is
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interpreted as an absolute path to a file containing the encryption
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password. For swap encryption, <filename>/dev/urandom</filename>
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or the hardware device <filename>/dev/hw_random</filename> can be
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used as the password file; using <filename>/dev/random</filename>
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may prevent boot completion if the system does not have enough
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entropy to generate a truly random encryption key.</para>
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<para>The fourth field, if present, is a comma-delimited list of
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options. The following options are recognized:</para>
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<variablelist class='fstab-options'>
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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 project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of this option. A
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cipher with unpredictable IV values, such as
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<literal>aes-cbc-essiv:sha256</literal>, is
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recommended.</para></listitem>
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</varlistentry>
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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 passed through the encrypted block
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device. This improves performance on SSD storage but has security implications.
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</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 password
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hashing. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of this
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option.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>header=</option></term>
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<listitem><para>Use a detached (separated) metadata device or
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file where the LUKS header is stored. This option is only
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relevant for LUKS devices. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of this
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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 skip at the
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start of the key file. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of this
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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 of bytes to read
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from the key file. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of this option. This
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option is ignored in plain encryption mode, as the key file
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size is then 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 compare the
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passphrase or key against. If the key slot does not match the
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given passphrase or key, but another would, the setup of the
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device will fail regardless. This option implies
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<option>luks</option>. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values. The default is to try all key slots in
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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 is used, the
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following options are ignored since they are provided by the
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LUKS header on the 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>_netdev</option></term>
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<listitem><para>Marks this cryptsetup device as requiring network. It will be
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started after the network is available, similarly to
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<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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units marked with <option>_netdev</option>. The service unit to set up this device
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will be ordered between <filename>remote-fs-pre.target</filename> and
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<filename>remote-cryptsetup.target</filename>, instead of
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<filename>cryptsetup-pre.target</filename> and
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<filename>cryptsetup.target</filename>.</para>
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<para>Hint: if this device is used for a mount point that is specified in
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<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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the <option>_netdev</option> option should also be used for the mount
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point. Otherwise, a dependency loop might be created where the mount point
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will be pulled in by <filename>local-fs.target</filename>, while the
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service to configure the network is usually only started <emphasis>after</emphasis>
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the local file system has been mounted.</para>
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</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 added to <filename>cryptsetup.target</filename>.
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This means that it will not be automatically unlocked on boot, unless something else pulls
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it in. In particular, if the device is used for a mount point, it'll be unlocked
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automatically during boot, unless the mount point itself is also disabled with
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<option>noauto</option>.</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>This device will not be a hard dependency of
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<filename>cryptsetup.target</filename>. It'll be still pulled in and started, but the system
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will not wait for the device to show up and be unlocked, and boot will not fail if this is
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unsuccessful. Note that other units that depend on the unlocked device may still fail. In
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particular, if the device is used for a mount point, the mount point itself is also needs to
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have <option>noauto</option> option, or the boot will fail if the device is not unlocked
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successfully.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>offset=</option></term>
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<listitem><para>Start offset in the backend device, in 512-byte sectors. This
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option is only relevant for plain devices.</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 device in read-only
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mode.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>skip=</option></term>
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<listitem><para>How many 512-byte sectors of the encrypted data to skip at the
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beginning. This is different from the <option>offset=</option> option with respect
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to the sector numbers used in initialization vector (IV) calculation. Using
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<option>offset=</option> will shift the IV calculation by the same negative
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amount. Hence, if <option>offset=<replaceable>n</replaceable></option> is given,
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sector <replaceable>n</replaceable> will get a sector number of 0 for the IV
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calculation. Using <option>skip=</option> causes sector
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<replaceable>n</replaceable> to also be the first sector of the mapped device, but
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with its number for IV generation being <replaceable>n</replaceable>.</para>
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<para>This option is only relevant for plain devices.</para>
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</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 in bits. See
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for possible values and the default value of this
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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 be used as a
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swap device, and will be formatted accordingly after setting
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up the encrypted block device, with
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<citerefentry project='man-pages'><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> option will
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destroy the contents of the named partition during every boot,
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so make sure the underlying block device is specified
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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. When this mode
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is used, the following options are ignored since they are
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provided by the TrueCrypt header on the device or do not
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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 read from the
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key file given in the third field. Only the first line of this
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file is read, excluding the new line character.</para>
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<para>Note that the TrueCrypt format uses both passphrase and
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key files to derive a password for the volume. Therefore, the
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passphrase and all key files need to be provided. Use
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<option>tcrypt-keyfile=</option> to provide the absolute path
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to all key files. When using an empty passphrase in
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combination with one or more key files, use
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<literal>/dev/null</literal> as the password file in the third
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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. This option
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implies <option>tcrypt</option>.</para>
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<para>This will map the hidden volume that is inside of the
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volume provided in the second field. Please note that there is
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no protection for the hidden volume if the outer volume is
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mounted instead. See
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<citerefentry project='die-net'><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 key file to
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use for a TrueCrypt volume. This implies
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<option>tcrypt</option> and can be used more than once to
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provide several key files.</para>
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<para>See the entry for <option>tcrypt</option> on the
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behavior of the passphrase and key files when using TrueCrypt
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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 encryption mode. This
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option implies <option>tcrypt</option>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>tcrypt-veracrypt</option></term>
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<listitem><para>Check for a VeraCrypt volume. VeraCrypt is a fork of
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TrueCrypt that is mostly compatible, but uses different, stronger key
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derivation algorithms that cannot be detected without this flag.
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Enabling this option could substantially slow down unlocking, because
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VeraCrypt's key derivation takes much longer than TrueCrypt's. This
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option implies <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 querying for a
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password. If no unit is specified, seconds is used. Supported
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units are 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 be prepared
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for using it as <filename>/tmp</filename>; it will be
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formatted using
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<citerefentry project='man-pages'><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> option will
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destroy the contents of the named partition during every boot,
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so make sure the underlying block device is specified
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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 times the user
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is queried for a password. The default is 3. If set to 0, the
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user is 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 read from
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console, it has to be entered twice to prevent
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typos.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>x-systemd.device-timeout=</option></term>
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<listitem><para>Specifies how long systemd should wait for a device to show up
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before giving up on the entry. The argument is a time in seconds or explicitly
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specified units of
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<literal>s</literal>,
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<literal>min</literal>,
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<literal>h</literal>,
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<literal>ms</literal>.
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</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 configuration is
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reloaded, this file is translated into native systemd units by
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<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 LUKS for
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normal storage, another one for usage as a swap device and two
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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 project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><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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