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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">

<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 a absolute path to a file containing the encryption

password. For swap encryption, <filename>/dev/urandom</filename>

or the hardware device <filename>/dev/hw_random</filename> can be

used as the password file; using <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>,

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 is 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>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>