3 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5 This file is part of systemd.
7 Copyright 2012 Lennart Poettering
9 systemd is free software; you can redistribute it and/or modify it
10 under the terms of the GNU Lesser General Public License as published by
11 the Free Software Foundation; either version 2.1 of the License, or
12 (at your option) any later version.
14 systemd is distributed in the hope that it will be useful, but
15 WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 Lesser General Public License for more details.
19 You should have received a copy of the GNU Lesser General Public License
20 along with systemd; If not, see <http://www.gnu.org/licenses/>.
22 This is based on crypttab(5) from Fedora's initscripts package, which in
23 turn is based on Debian's version.
25 The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
28 <refentry id=
"crypttab" conditional='HAVE_LIBCRYPTSETUP'
>
31 <title>crypttab
</title>
32 <productname>systemd
</productname>
36 <contrib>Documentation
</contrib>
37 <firstname>Miloslav
</firstname>
38 <surname>Trmac
</surname>
39 <email>mitr@redhat.com
</email>
42 <contrib>Documentation
</contrib>
43 <firstname>Lennart
</firstname>
44 <surname>Poettering
</surname>
45 <email>lennart@poettering.net
</email>
51 <refentrytitle>crypttab
</refentrytitle>
52 <manvolnum>5</manvolnum>
56 <refname>crypttab
</refname>
57 <refpurpose>Configuration for encrypted block devices
</refpurpose>
61 <para><filename>/etc/crypttab
</filename></para>
65 <title>Description
</title>
67 <para>The
<filename>/etc/crypttab
</filename> file describes
68 encrypted block devices that are set up during system boot.
</para>
70 <para>Empty lines and lines starting with the
<literal>#
</literal>
71 character are ignored. Each of the remaining lines describes one
72 encrypted block device. Fields are delimited by white space.
</para>
74 <para>Each line is in the form
<programlisting><replaceable>name
</replaceable> <replaceable>encrypted-device
</replaceable> <replaceable>password
</replaceable> <replaceable>options
</replaceable></programlisting>
75 The first two fields are mandatory, the remaining two are
78 <para>Setting up encrypted block devices using this file supports
79 three encryption modes: LUKS, TrueCrypt and plain. See
80 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
81 for more information about each mode. When no mode is specified in
82 the options field and the block device contains a LUKS signature,
83 it is opened as a LUKS device; otherwise, it is assumed to be in
84 raw dm-crypt (plain mode) format.
</para>
86 <para>The first field contains the name of the resulting encrypted
87 block device; the device is set up within
88 <filename>/dev/mapper/
</filename>.
</para>
90 <para>The second field contains a path to the underlying block
91 device or file, or a specification of a block device via
92 <literal>UUID=
</literal> followed by the UUID.
</para>
94 <para>The third field specifies the encryption password. If the
95 field is not present or the password is set to
96 <literal>none
</literal> or
<literal>-
</literal>, the password has
97 to be manually entered during system boot. Otherwise, the field is
98 interpreted as an absolute path to a file containing the encryption
99 password. For swap encryption,
<filename>/dev/urandom
</filename>
100 or the hardware device
<filename>/dev/hw_random
</filename> can be
101 used as the password file; using
<filename>/dev/random
</filename>
102 may prevent boot completion if the system does not have enough
103 entropy to generate a truly random encryption key.
</para>
105 <para>The fourth field, if present, is a comma-delimited list of
106 options. The following options are recognized:
</para>
108 <variablelist class='fstab-options'
>
111 <term><option>cipher=
</option></term>
113 <listitem><para>Specifies the cipher to use. See
114 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
115 for possible values and the default value of this option. A
116 cipher with unpredictable IV values, such as
117 <literal>aes-cbc-essiv:sha256
</literal>, is
118 recommended.
</para></listitem>
122 <term><option>discard
</option></term>
124 <listitem><para>Allow discard requests to be passed through the encrypted block
125 device. This improves performance on SSD storage but has security implications.
130 <term><option>hash=
</option></term>
132 <listitem><para>Specifies the hash to use for password
134 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
135 for possible values and the default value of this
136 option.
</para></listitem>
140 <term><option>header=
</option></term>
142 <listitem><para>Use a detached (separated) metadata device or
143 file where the LUKS header is stored. This option is only
144 relevant for LUKS devices. See
145 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
146 for possible values and the default value of this
147 option.
</para></listitem>
151 <term><option>keyfile-offset=
</option></term>
153 <listitem><para>Specifies the number of bytes to skip at the
154 start of the key file. See
155 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
156 for possible values and the default value of this
157 option.
</para></listitem>
161 <term><option>keyfile-size=
</option></term>
163 <listitem><para>Specifies the maximum number of bytes to read
164 from the key file. See
165 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
166 for possible values and the default value of this option. This
167 option is ignored in plain encryption mode, as the key file
168 size is then given by the key size.
</para></listitem>
172 <term><option>key-slot=
</option></term>
174 <listitem><para>Specifies the key slot to compare the
175 passphrase or key against. If the key slot does not match the
176 given passphrase or key, but another would, the setup of the
177 device will fail regardless. This option implies
178 <option>luks
</option>. See
179 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
180 for possible values. The default is to try all key slots in
181 sequential order.
</para></listitem>
185 <term><option>luks
</option></term>
187 <listitem><para>Force LUKS mode. When this mode is used, the
188 following options are ignored since they are provided by the
189 LUKS header on the device:
<option>cipher=
</option>,
190 <option>hash=
</option>,
191 <option>size=
</option>.
</para></listitem>
195 <term><option>_netdev
</option></term>
197 <listitem><para>Marks this cryptsetup device as requiring network. It will be
198 started after the network is available, similarly to
199 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
200 units marked with
<option>_netdev
</option>. The service unit to set up this device
201 will be ordered between
<filename>remote-fs-pre.target
</filename> and
202 <filename>remote-cryptsetup.target
</filename>, instead of
203 <filename>cryptsetup-pre.target
</filename> and
204 <filename>cryptsetup.target
</filename>.
</para>
206 <para>Hint: if this device is used for a mount point that is specified in
207 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
208 the
<option>_netdev
</option> option should also be used for the mount
209 point. Otherwise, a dependency loop might be created where the mount point
210 will be pulled in by
<filename>local-fs.target
</filename>, while the
211 service to configure the network is usually only started
<emphasis>after
</emphasis>
212 the local file system has been mounted.
</para>
217 <term><option>noauto
</option></term>
219 <listitem><para>This device will not be automatically unlocked
220 on boot.
</para></listitem>
224 <term><option>nofail
</option></term>
226 <listitem><para>The system will not wait for the device to
227 show up and be unlocked at boot, and not fail the boot if it
228 does not show up.
</para></listitem>
232 <term><option>offset=
</option></term>
234 <listitem><para>Start offset in the backend device, in
512-byte sectors. This
235 option is only relevant for plain devices.
</para></listitem>
239 <term><option>plain
</option></term>
241 <listitem><para>Force plain encryption mode.
</para></listitem>
245 <term><option>read-only
</option></term><term><option>readonly
</option></term>
247 <listitem><para>Set up the encrypted block device in read-only
248 mode.
</para></listitem>
252 <term><option>skip=
</option></term>
254 <listitem><para>How many
512-byte sectors of the encrypted data to skip at the
255 beginning. This is different from the
<option>offset=
</option> option with respect
256 to the sector numbers used in initialization vector (IV) calculation. Using
257 <option>offset=
</option> will shift the IV calculation by the same negative
258 amount. Hence, if
<option>offset=
<replaceable>n
</replaceable></option> is given,
259 sector
<replaceable>n
</replaceable> will get a sector number of
0 for the IV
260 calculation. Using
<option>skip=
</option> causes sector
261 <replaceable>n
</replaceable> to also be the first sector of the mapped device, but
262 with its number for IV generation being
<replaceable>n
</replaceable>.
</para>
264 <para>This option is only relevant for plain devices.
</para>
269 <term><option>size=
</option></term>
271 <listitem><para>Specifies the key size in bits. See
272 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
273 for possible values and the default value of this
274 option.
</para></listitem>
278 <term><option>swap
</option></term>
280 <listitem><para>The encrypted block device will be used as a
281 swap device, and will be formatted accordingly after setting
282 up the encrypted block device, with
283 <citerefentry project='man-pages'
><refentrytitle>mkswap
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
284 This option implies
<option>plain
</option>.
</para>
286 <para>WARNING: Using the
<option>swap
</option> option will
287 destroy the contents of the named partition during every boot,
288 so make sure the underlying block device is specified
289 correctly.
</para></listitem>
293 <term><option>tcrypt
</option></term>
295 <listitem><para>Use TrueCrypt encryption mode. When this mode
296 is used, the following options are ignored since they are
297 provided by the TrueCrypt header on the device or do not
299 <option>cipher=
</option>,
300 <option>hash=
</option>,
301 <option>keyfile-offset=
</option>,
302 <option>keyfile-size=
</option>,
303 <option>size=
</option>.
</para>
305 <para>When this mode is used, the passphrase is read from the
306 key file given in the third field. Only the first line of this
307 file is read, excluding the new line character.
</para>
309 <para>Note that the TrueCrypt format uses both passphrase and
310 key files to derive a password for the volume. Therefore, the
311 passphrase and all key files need to be provided. Use
312 <option>tcrypt-keyfile=
</option> to provide the absolute path
313 to all key files. When using an empty passphrase in
314 combination with one or more key files, use
315 <literal>/dev/null
</literal> as the password file in the third
316 field.
</para></listitem>
320 <term><option>tcrypt-hidden
</option></term>
322 <listitem><para>Use the hidden TrueCrypt volume. This option
323 implies
<option>tcrypt
</option>.
</para>
325 <para>This will map the hidden volume that is inside of the
326 volume provided in the second field. Please note that there is
327 no protection for the hidden volume if the outer volume is
329 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
330 for more information on this limitation.
</para></listitem>
334 <term><option>tcrypt-keyfile=
</option></term>
336 <listitem><para>Specifies the absolute path to a key file to
337 use for a TrueCrypt volume. This implies
338 <option>tcrypt
</option> and can be used more than once to
339 provide several key files.
</para>
341 <para>See the entry for
<option>tcrypt
</option> on the
342 behavior of the passphrase and key files when using TrueCrypt
343 encryption mode.
</para></listitem>
347 <term><option>tcrypt-system
</option></term>
349 <listitem><para>Use TrueCrypt in system encryption mode. This
350 option implies
<option>tcrypt
</option>.
</para></listitem>
354 <term><option>tcrypt-veracrypt
</option></term>
356 <listitem><para>Check for a VeraCrypt volume. VeraCrypt is a fork of
357 TrueCrypt that is mostly compatible, but uses different, stronger key
358 derivation algorithms that cannot be detected without this flag.
359 Enabling this option could substantially slow down unlocking, because
360 VeraCrypt's key derivation takes much longer than TrueCrypt's. This
361 option implies
<option>tcrypt
</option>.
</para></listitem>
365 <term><option>timeout=
</option></term>
367 <listitem><para>Specifies the timeout for querying for a
368 password. If no unit is specified, seconds is used. Supported
369 units are s, ms, us, min, h, d. A timeout of
0 waits
370 indefinitely (which is the default).
</para></listitem>
374 <term><option>tmp
</option></term>
376 <listitem><para>The encrypted block device will be prepared
377 for using it as
<filename>/tmp
</filename>; it will be
379 <citerefentry project='man-pages'
><refentrytitle>mke2fs
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
380 This option implies
<option>plain
</option>.
</para>
382 <para>WARNING: Using the
<option>tmp
</option> option will
383 destroy the contents of the named partition during every boot,
384 so make sure the underlying block device is specified
385 correctly.
</para></listitem>
389 <term><option>tries=
</option></term>
391 <listitem><para>Specifies the maximum number of times the user
392 is queried for a password. The default is
3. If set to
0, the
393 user is queried for a password indefinitely.
</para></listitem>
397 <term><option>verify
</option></term>
399 <listitem><para> If the encryption password is read from
400 console, it has to be entered twice to prevent
401 typos.
</para></listitem>
405 <term><option>x-systemd.device-timeout=
</option></term>
407 <listitem><para>Specifies how long systemd should wait for a device to show up
408 before giving up on the entry. The argument is a time in seconds or explicitly
410 <literal>s
</literal>,
411 <literal>min
</literal>,
412 <literal>h
</literal>,
413 <literal>ms
</literal>.
419 <para>At early boot and when the system manager configuration is
420 reloaded, this file is translated into native systemd units by
421 <citerefentry><refentrytitle>systemd-cryptsetup-generator
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para>
425 <title>Example
</title>
427 <title>/etc/crypttab example
</title>
428 <para>Set up four encrypted block devices. One using LUKS for
429 normal storage, another one for usage as a swap device and two
430 TrueCrypt volumes.
</para>
432 <programlisting>luks UUID=
2505567a-
9e27-
4efe-a4d5-
15ad146c258b
433 swap /dev/sda7 /dev/urandom swap
434 truecrypt /dev/sda2 /etc/container_password tcrypt
435 hidden /mnt/tc_hidden /dev/null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
</programlisting>
440 <title>See Also
</title>
442 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
443 <citerefentry><refentrytitle>systemd-cryptsetup@.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
444 <citerefentry><refentrytitle>systemd-cryptsetup-generator
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
445 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
446 <citerefentry project='die-net'
><refentrytitle>cryptsetup
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
447 <citerefentry project='man-pages'
><refentrytitle>mkswap
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
448 <citerefentry project='man-pages'
><refentrytitle>mke2fs
</refentrytitle><manvolnum>8</manvolnum></citerefentry>