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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
This is based on crypttab(5) from Fedora's initscripts package, which in
turn is based on Debian's version.
The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
-->
<refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP'>
<refentryinfo>
<title>crypttab</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Documentation</contrib>
<firstname>Miloslav</firstname>
<surname>Trmac</surname>
<email>mitr@redhat.com</email>
</author>
<author>
<contrib>Documentation</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>crypttab</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>crypttab</refname>
<refpurpose>Configuration for encrypted block devices</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/crypttab</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The <filename>/etc/crypttab</filename> file describes
encrypted block devices that are set up during system boot.</para>
<para>Empty lines and lines starting with the <literal>#</literal>
character are ignored. Each of the remaining lines describes one
encrypted block device, fields on the line are delimited by white
space. The first two fields are mandatory, the remaining two are
optional.</para>
<para>Setting up encrypted block devices using this file supports
three encryption modes: LUKS, TrueCrypt and plain. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for more information about each mode. When no mode is specified in
the options field and the block device contains a LUKS signature,
it is opened as a LUKS device; otherwise, it is assumed to be in
raw dm-crypt (plain mode) format.</para>
<para>The first field contains the name of the resulting encrypted
block device; the device is set up within
<filename>/dev/mapper/</filename>.</para>
<para>The second field contains a path to the underlying block
device or file, or a specification of a block device via
<literal>UUID=</literal> followed by the UUID.</para>
<para>The third field specifies the encryption password. If the
field is not present or the password is set to
<literal>none</literal> or <literal>-</literal>, the password has
to be manually entered during system boot. Otherwise, the field is
interpreted as an absolute path to a file containing the encryption
password. For swap encryption, <filename>/dev/urandom</filename>
or the hardware device <filename>/dev/hw_random</filename> can be
used as the password file; using <filename>/dev/random</filename>
may prevent boot completion if the system does not have enough
entropy to generate a truly random encryption key.</para>
<para>The fourth field, if present, is a comma-delimited list of
options. The following options are recognized:</para>
<variablelist class='fstab-options'>
<varlistentry>
<term><option>discard</option></term>
<listitem><para>Allow discard requests to be passed through
the encrypted block device. This improves performance on SSD
storage but has security implications.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>cipher=</option></term>
<listitem><para>Specifies the cipher to use. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default value of this option. A
cipher with unpredictable IV values, such as
<literal>aes-cbc-essiv:sha256</literal>, is
recommended.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>hash=</option></term>
<listitem><para>Specifies the hash to use for password
hashing. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default value of this
option.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>header=</option></term>
<listitem><para>Use a detached (separated) metadata device or
file where the LUKS header is stored. This option is only
relevant for LUKS devices. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default value of this
option.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>offset=</option></term>
<listitem><para>Start offset in the backend device, in 512-byte sectors.
This option is only relevant for plain devices.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>skip=</option></term>
<listitem><para>How many 512-byte sectors of the encrypted data to skip
at the beginning. This is different from the <option>--offset</option>
option with respect to the sector numbers used in initialization vector
(IV) calculation. Using <option>--offset</option> will shift the IV
calculation by the same negative amount. Hence, if <option>--offset n</option> is given,
sector n will get a sector number of 0 for the IV calculation.
Using <option>--skip</option> causes sector n to also be the first
sector of the mapped device, but with its number for IV generation being n.</para>
<para>This option is only relevant for plain devices.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>keyfile-offset=</option></term>
<listitem><para>Specifies the number of bytes to skip at the
start of the key file. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default value of this
option.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>keyfile-size=</option></term>
<listitem><para>Specifies the maximum number of bytes to read
from the key file. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default value of this option. This
option is ignored in plain encryption mode, as the key file
size is then given by the key size.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>key-slot=</option></term>
<listitem><para>Specifies the key slot to compare the
passphrase or key against. If the key slot does not match the
given passphrase or key, but another would, the setup of the
device will fail regardless. This option implies
<option>luks</option>. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values. The default is to try all key slots in
sequential order.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>luks</option></term>
<listitem><para>Force LUKS mode. When this mode is used, the
following options are ignored since they are provided by the
LUKS header on the device: <option>cipher=</option>,
<option>hash=</option>,
<option>size=</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>noauto</option></term>
<listitem><para>This device will not be automatically unlocked
on boot.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>nofail</option></term>
<listitem><para>The system will not wait for the device to
show up and be unlocked at boot, and not fail the boot if it
does not show up.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>plain</option></term>
<listitem><para>Force plain encryption mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>read-only</option></term><term><option>readonly</option></term>
<listitem><para>Set up the encrypted block device in read-only
mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>size=</option></term>
<listitem><para>Specifies the key size in bits. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default value of this
option.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>swap</option></term>
<listitem><para>The encrypted block device will be used as a
swap device, and will be formatted accordingly after setting
up the encrypted block device, with
<citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
This option implies <option>plain</option>.</para>
<para>WARNING: Using the <option>swap</option> option will
destroy the contents of the named partition during every boot,
so make sure the underlying block device is specified
correctly.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tcrypt</option></term>
<listitem><para>Use TrueCrypt encryption mode. When this mode
is used, the following options are ignored since they are
provided by the TrueCrypt header on the device or do not
apply:
<option>cipher=</option>,
<option>hash=</option>,
<option>keyfile-offset=</option>,
<option>keyfile-size=</option>,
<option>size=</option>.</para>
<para>When this mode is used, the passphrase is read from the
key file given in the third field. Only the first line of this
file is read, excluding the new line character.</para>
<para>Note that the TrueCrypt format uses both passphrase and
key files to derive a password for the volume. Therefore, the
passphrase and all key files need to be provided. Use
<option>tcrypt-keyfile=</option> to provide the absolute path
to all key files. When using an empty passphrase in
combination with one or more key files, use
<literal>/dev/null</literal> as the password file in the third
field.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tcrypt-hidden</option></term>
<listitem><para>Use the hidden TrueCrypt volume. This option
implies <option>tcrypt</option>.</para>
<para>This will map the hidden volume that is inside of the
volume provided in the second field. Please note that there is
no protection for the hidden volume if the outer volume is
mounted instead. See
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for more information on this limitation.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tcrypt-keyfile=</option></term>
<listitem><para>Specifies the absolute path to a key file to
use for a TrueCrypt volume. This implies
<option>tcrypt</option> and can be used more than once to
provide several key files.</para>
<para>See the entry for <option>tcrypt</option> on the
behavior of the passphrase and key files when using TrueCrypt
encryption mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tcrypt-system</option></term>
<listitem><para>Use TrueCrypt in system encryption mode. This
option implies <option>tcrypt</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tcrypt-veracrypt</option></term>
<listitem><para>Check for a VeraCrypt volume. VeraCrypt is a fork of
TrueCrypt that is mostly compatible, but uses different, stronger key
derivation algorithms that cannot be detected without this flag.
Enabling this option could substantially slow down unlocking, because
VeraCrypt's key derivation takes much longer than TrueCrypt's. This
option implies <option>tcrypt</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>timeout=</option></term>
<listitem><para>Specifies the timeout for querying for a
password. If no unit is specified, seconds is used. Supported
units are s, ms, us, min, h, d. A timeout of 0 waits
indefinitely (which is the default).</para></listitem>
</varlistentry>
<varlistentry>
<term><option>x-systemd.device-timeout=</option></term>
<listitem><para>Specifies how long systemd should wait for a
device to show up before giving up on the entry. The argument
is a time in seconds or explicitly specified units of
<literal>s</literal>,
<literal>min</literal>,
<literal>h</literal>,
<literal>ms</literal>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tmp</option></term>
<listitem><para>The encrypted block device will be prepared
for using it as <filename>/tmp</filename>; it will be
formatted using
<citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
This option implies <option>plain</option>.</para>
<para>WARNING: Using the <option>tmp</option> option will
destroy the contents of the named partition during every boot,
so make sure the underlying block device is specified
correctly.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>tries=</option></term>
<listitem><para>Specifies the maximum number of times the user
is queried for a password. The default is 3. If set to 0, the
user is queried for a password indefinitely.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>verify</option></term>
<listitem><para> If the encryption password is read from
console, it has to be entered twice to prevent
typos.</para></listitem>
</varlistentry>
</variablelist>
<para>At early boot and when the system manager configuration is
reloaded, this file is translated into native systemd units by
<citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>Example</title>
<example>
<title>/etc/crypttab example</title>
<para>Set up four encrypted block devices. One using LUKS for
normal storage, another one for usage as a swap device and two
TrueCrypt volumes.</para>
<programlisting>luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
swap /dev/sda7 /dev/urandom swap
truecrypt /dev/sda2 /etc/container_password tcrypt
hidden /mnt/tc_hidden /dev/null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
</example>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
|
