chiark / gitweb /
namespace: include boot id in private tmp directories
[elogind.git] / man / crypttab.xml
1 <?xml version="1.0"?>
2 <!--*-nxml-*-->
3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!--
5   This file is part of systemd.
6
7   Copyright 2012 Lennart Poettering
8
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.
13
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.
18
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/>.
21
22   This is based on crypttab(5) from Fedora's initscripts package, which in
23   turn is based on Debian's version.
24
25   The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
26
27 -->
28 <refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP'>
29
30         <refentryinfo>
31                 <title>crypttab</title>
32                 <productname>systemd</productname>
33
34                 <authorgroup>
35                         <author>
36                                 <contrib>Documentation</contrib>
37                                 <firstname>Miloslav</firstname>
38                                 <surname>Trmac</surname>
39                                 <email>mitr@redhat.com</email>
40                         </author>
41                         <author>
42                                 <contrib>Documentation</contrib>
43                                 <firstname>Lennart</firstname>
44                                 <surname>Poettering</surname>
45                                 <email>lennart@poettering.net</email>
46                         </author>
47                 </authorgroup>
48         </refentryinfo>
49
50         <refmeta>
51                 <refentrytitle>crypttab</refentrytitle>
52                 <manvolnum>5</manvolnum>
53         </refmeta>
54
55         <refnamediv>
56                 <refname>crypttab</refname>
57                 <refpurpose>Configuration for encrypted block devices</refpurpose>
58         </refnamediv>
59
60         <refsynopsisdiv>
61                 <para><filename>/etc/crypttab</filename></para>
62         </refsynopsisdiv>
63
64         <refsect1>
65                 <title>Description</title>
66
67                 <para>The <filename>/etc/crypttab</filename> file
68                 describes encrypted block devices that are set up
69                 during system boot.</para>
70
71                 <para>Empty lines and lines starting with the <literal>#</literal>
72                 character are ignored.  Each of the remaining lines
73                 describes one encrypted block device, fields on the
74                 line are delimited by white space.  The first two
75                 fields are mandatory, the remaining two are
76                 optional.</para>
77
78                 <para>Setting up encrypted block devices using this file
79                 supports three encryption modes: LUKS, TrueCrypt and plain.
80                 See <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
81                 for more information about each mode. When no mode is specified
82                 in the options field and the block device contains a LUKS
83                 signature, it is opened as a LUKS device; otherwise, it is
84                 assumed to be in raw dm-crypt (plain mode) format.</para>
85
86                 <para>The first field contains the name of the
87                 resulting encrypted block device; the device is set up
88                 within <filename>/dev/mapper/</filename>.</para>
89
90                 <para>The second field contains a path to the
91                 underlying block device or file, or a specification of a block
92                 device via <literal>UUID=</literal> followed by the
93                 UUID.</para>
94
95                 <para>The third field specifies the encryption
96                 password.  If the field is not present or the password
97                 is set to <literal>none</literal> or <literal>-</literal>,
98                 the password has to be manually entered during system boot.
99                 Otherwise, the field is interpreted as a absolute path to
100                 a file containing the encryption password. For swap encryption,
101                 <filename>/dev/urandom</filename> or the hardware
102                 device <filename>/dev/hw_random</filename> can be used
103                 as the password file; using
104                 <filename>/dev/random</filename> may prevent boot
105                 completion if the system does not have enough entropy
106                 to generate a truly random encryption key.</para>
107
108                 <para>The fourth field, if present, is a
109                 comma-delimited list of options.  The following
110                 options are recognized:</para>
111
112                 <variablelist class='crypttab-options'>
113
114                         <varlistentry>
115                                 <term><varname>discard</varname></term>
116
117                                 <listitem><para>Allow discard requests to be
118                                 passed through the encrypted block device. This
119                                 improves performance on SSD storage but has
120                                 security implications.</para></listitem>
121                         </varlistentry>
122
123                         <varlistentry>
124                                 <term><varname>cipher=</varname></term>
125
126                                 <listitem><para>Specifies the cipher to use. See
127                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
128                                 for possible values and the default value of
129                                 this option. A cipher with unpredictable IV
130                                 values, such as <literal>aes-cbc-essiv:sha256</literal>,
131                                 is recommended.</para></listitem>
132                         </varlistentry>
133
134                         <varlistentry>
135                                 <term><varname>hash=</varname></term>
136
137                                 <listitem><para>Specifies the hash to use for
138                                 password hashing. See
139                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
140                                 for possible values and the default value of
141                                 this option.</para></listitem>
142                         </varlistentry>
143
144                         <varlistentry>
145                                 <term><varname>keyfile-offset=</varname></term>
146
147                                 <listitem><para>Specifies the number of bytes to
148                                 skip at the start of the key file. See
149                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
150                                 for possible values and the default value of
151                                 this option.</para></listitem>
152                         </varlistentry>
153
154                         <varlistentry>
155                                 <term><varname>keyfile-size=</varname></term>
156
157                                 <listitem><para>Specifies the maximum number
158                                 of bytes to read from the key file. See
159                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
160                                 for possible values and the default value of
161                                 this option. This option is ignored in plain
162                                 encryption mode, as the key file size is then
163                                 given by the key size.</para></listitem>
164                         </varlistentry>
165
166                         <varlistentry>
167                                 <term><varname>luks</varname></term>
168
169                                 <listitem><para>Force LUKS mode. When this mode
170                                 is used, the following options are ignored since
171                                 they are provided by the LUKS header on the
172                                 device: <varname>cipher=</varname>,
173                                 <varname>hash=</varname>,
174                                 <varname>size=</varname>.</para></listitem>
175                         </varlistentry>
176
177                         <varlistentry>
178                                 <term><varname>noauto</varname></term>
179
180                                 <listitem><para>This device will not be
181                                 automatically unlocked on boot.</para></listitem>
182                         </varlistentry>
183
184                         <varlistentry>
185                                 <term><varname>nofail</varname></term>
186
187                                 <listitem><para>The system will not wait for the
188                                 device to show up and be unlocked at boot, and
189                                 not fail the boot if it does not show up.</para></listitem>
190                         </varlistentry>
191
192                         <varlistentry>
193                                 <term><varname>plain</varname></term>
194
195                                 <listitem><para>Force plain encryption mode.</para></listitem>
196                         </varlistentry>
197
198                         <varlistentry>
199                                 <term><varname>read-only</varname></term><term><varname>readonly</varname></term>
200
201                                 <listitem><para>Set up the encrypted block
202                                 device in read-only mode.</para></listitem>
203                         </varlistentry>
204
205                         <varlistentry>
206                                 <term><varname>size=</varname></term>
207
208                                 <listitem><para>Specifies the key size
209                                 in bits. See
210                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
211                                 for possible values and the default value of
212                                 this option.</para></listitem>
213                         </varlistentry>
214
215                         <varlistentry>
216                                 <term><varname>swap</varname></term>
217
218                                 <listitem><para>The encrypted block device will
219                                 be used as a swap device, and will be formatted
220                                 accordingly after setting up the encrypted
221                                 block device, with
222                                 <citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
223                                 This option implies <varname>plain</varname>.</para>
224
225                                 <para>WARNING: Using the <varname>swap</varname>
226                                 option will destroy the contents of the named
227                                 partition during every boot, so make sure the
228                                 underlying block device is specified correctly.</para></listitem>
229                         </varlistentry>
230
231                         <varlistentry>
232                                 <term><varname>tcrypt</varname></term>
233
234                                 <listitem><para>Use TrueCrypt encryption mode.
235                                 When this mode is used, the following options are
236                                 ignored since they are provided by the TrueCrypt
237                                 header on the device or do not apply:
238                                 <varname>cipher=</varname>,
239                                 <varname>hash=</varname>,
240                                 <varname>keyfile-offset=</varname>,
241                                 <varname>keyfile-size=</varname>,
242                                 <varname>size=</varname>.</para>
243
244                                 <para>When this mode is used, the passphrase is
245                                 read from the key file given in the third field.
246                                 Only the first line of this file is read,
247                                 excluding the new line character.</para>
248
249                                 <para>Note that the TrueCrypt format uses both
250                                 passphrase and key files to derive a password
251                                 for the volume. Therefore, the passphrase and
252                                 all key files need to be provided. Use
253                                 <varname>tcrypt-keyfile=</varname> to provide
254                                 the absolute path to all key files. When using
255                                 an empty passphrase in combination with one or
256                                 more key files, use <literal>/dev/null</literal>
257                                 as the password file in the third field.</para></listitem>
258                         </varlistentry>
259
260                         <varlistentry>
261                                 <term><varname>tcrypt-hidden</varname></term>
262
263                                 <listitem><para>Use the hidden TrueCrypt volume.
264                                 This implies <varname>tcrypt</varname>.</para>
265
266                                 <para>This will map the hidden volume that is
267                                 inside of the volume provided in the second
268                                 field. Please note that there is no protection
269                                 for the hidden volume if the outer volume is
270                                 mounted instead. See
271                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
272                                 for more information on this limitation.</para></listitem>
273                         </varlistentry>
274
275                         <varlistentry>
276                                 <term><varname>tcrypt-keyfile=</varname></term>
277
278                                 <listitem><para>Specifies the absolute path to a
279                                 key file to use for a TrueCrypt volume. This
280                                 implies <varname>tcrypt</varname> and can be
281                                 used more than once to provide several key
282                                 files.</para>
283
284                                 <para>See the entry for <varname>tcrypt</varname>
285                                 on the behavior of the passphrase and key files
286                                 when using TrueCrypt encryption mode.</para></listitem>
287                         </varlistentry>
288
289                         <varlistentry>
290                                 <term><varname>tcrypt-system</varname></term>
291
292                                 <listitem><para>Use TrueCrypt in system
293                                 encryption mode. This implies
294                                 <varname>tcrypt</varname>.</para>
295
296                                 <para>Please note that when using this mode, the
297                                 whole device needs to be given in the second
298                                 field instead of the partition. For example: if
299                                 <literal>/dev/sda2</literal> is the system
300                                 encrypted TrueCrypt patition, <literal>/dev/sda</literal>
301                                 has to be given.</para></listitem>
302                         </varlistentry>
303
304                         <varlistentry>
305                                 <term><varname>timeout=</varname></term>
306
307                                 <listitem><para>Specifies the timeout for
308                                 querying for a password. If no unit is
309                                 specified, seconds is used. Supported units are
310                                 s, ms, us, min, h, d. A timeout of 0 waits
311                                 indefinitely (which is the default).</para></listitem>
312                         </varlistentry>
313
314                         <varlistentry>
315                                 <term><varname>tmp</varname></term>
316
317                                 <listitem><para>The encrypted block device will
318                                 be prepared for using it as <filename>/tmp</filename>;
319                                 it will be formatted using
320                                 <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
321                                 This option implies <varname>plain</varname>.</para>
322
323                                 <para>WARNING: Using the <varname>tmp</varname>
324                                 option will destroy the contents of the named
325                                 partition during every boot, so make sure the
326                                 underlying block device is specified correctly.</para></listitem>
327                         </varlistentry>
328
329                         <varlistentry>
330                                 <term><varname>tries=</varname></term>
331
332                                 <listitem><para>Specifies the maximum number of
333                                 times the user is queried for a password.
334                                 The default is 3. If set to 0, the user is
335                                 queried for a password indefinitely.</para></listitem>
336                         </varlistentry>
337
338                         <varlistentry>
339                                 <term><varname>verify</varname></term>
340
341                                 <listitem><para> If the encryption password is
342                                 read from console, it has to be entered twice to
343                                 prevent typos.</para></listitem>
344                         </varlistentry>
345
346                 </variablelist>
347
348                 <para>At early boot and when the system manager
349                 configuration is reloaded, this file is translated into
350                 native systemd units
351                 by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
352         </refsect1>
353
354         <refsect1>
355                 <title>Example</title>
356                 <example>
357                         <title>/etc/crypttab example</title>
358                         <para>Set up four encrypted block devices. One using
359                         LUKS for normal storage, another one for usage as a swap
360                         device and two TrueCrypt volumes.</para>
361
362                         <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
363 swap       /dev/sda7       /dev/urandom             swap
364 truecrypt  /dev/sda2       /etc/container_password  tcrypt
365 hidden     /mnt/tc_hidden  /null                    tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
366                 </example>
367         </refsect1>
368
369         <refsect1>
370                 <title>See Also</title>
371                 <para>
372                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
373                         <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
374                         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
375                         <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
376                         <citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
377                         <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
378                 </para>
379         </refsect1>
380
381 </refentry>