chiark / gitweb /
run: add a new "-t" mode for invoking a binary on an allocated TTY
[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='fstab-options'>
113
114                         <varlistentry>
115                                 <term><option>discard</option></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><option>cipher=</option></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><option>hash=</option></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><option>keyfile-offset=</option></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><option>keyfile-size=</option></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><option>key-slot=</option></term>
168
169                                 <listitem><para>Specifies the key slot to
170                                 compare the passphrase or key against.
171                                 If the key slot does not match the given
172                                 passphrase or key, but another would, the
173                                 setup of the device will fail regardless.
174                                 This option implies <option>luks</option>. See
175                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
176                                 for possible values. The default is to try
177                                 all key slots in sequential order.</para></listitem>
178                         </varlistentry>
179
180                         <varlistentry>
181                                 <term><option>luks</option></term>
182
183                                 <listitem><para>Force LUKS mode. When this mode
184                                 is used, the following options are ignored since
185                                 they are provided by the LUKS header on the
186                                 device: <option>cipher=</option>,
187                                 <option>hash=</option>,
188                                 <option>size=</option>.</para></listitem>
189                         </varlistentry>
190
191                         <varlistentry>
192                                 <term><option>noauto</option></term>
193
194                                 <listitem><para>This device will not be
195                                 automatically unlocked on boot.</para></listitem>
196                         </varlistentry>
197
198                         <varlistentry>
199                                 <term><option>nofail</option></term>
200
201                                 <listitem><para>The system will not wait for the
202                                 device to show up and be unlocked at boot, and
203                                 not fail the boot if it does not show up.</para></listitem>
204                         </varlistentry>
205
206                         <varlistentry>
207                                 <term><option>plain</option></term>
208
209                                 <listitem><para>Force plain encryption mode.</para></listitem>
210                         </varlistentry>
211
212                         <varlistentry>
213                                 <term><option>read-only</option></term><term><option>readonly</option></term>
214
215                                 <listitem><para>Set up the encrypted block
216                                 device in read-only mode.</para></listitem>
217                         </varlistentry>
218
219                         <varlistentry>
220                                 <term><option>size=</option></term>
221
222                                 <listitem><para>Specifies the key size
223                                 in bits. See
224                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
225                                 for possible values and the default value of
226                                 this option.</para></listitem>
227                         </varlistentry>
228
229                         <varlistentry>
230                                 <term><option>swap</option></term>
231
232                                 <listitem><para>The encrypted block device will
233                                 be used as a swap device, and will be formatted
234                                 accordingly after setting up the encrypted
235                                 block device, with
236                                 <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
237                                 This option implies <option>plain</option>.</para>
238
239                                 <para>WARNING: Using the <option>swap</option>
240                                 option will destroy the contents of the named
241                                 partition during every boot, so make sure the
242                                 underlying block device is specified correctly.</para></listitem>
243                         </varlistentry>
244
245                         <varlistentry>
246                                 <term><option>tcrypt</option></term>
247
248                                 <listitem><para>Use TrueCrypt encryption mode.
249                                 When this mode is used, the following options are
250                                 ignored since they are provided by the TrueCrypt
251                                 header on the device or do not apply:
252                                 <option>cipher=</option>,
253                                 <option>hash=</option>,
254                                 <option>keyfile-offset=</option>,
255                                 <option>keyfile-size=</option>,
256                                 <option>size=</option>.</para>
257
258                                 <para>When this mode is used, the passphrase is
259                                 read from the key file given in the third field.
260                                 Only the first line of this file is read,
261                                 excluding the new line character.</para>
262
263                                 <para>Note that the TrueCrypt format uses both
264                                 passphrase and key files to derive a password
265                                 for the volume. Therefore, the passphrase and
266                                 all key files need to be provided. Use
267                                 <option>tcrypt-keyfile=</option> to provide
268                                 the absolute path to all key files. When using
269                                 an empty passphrase in combination with one or
270                                 more key files, use <literal>/dev/null</literal>
271                                 as the password file in the third field.</para></listitem>
272                         </varlistentry>
273
274                         <varlistentry>
275                                 <term><option>tcrypt-hidden</option></term>
276
277                                 <listitem><para>Use the hidden TrueCrypt volume.
278                                 This option implies <option>tcrypt</option>.</para>
279
280                                 <para>This will map the hidden volume that is
281                                 inside of the volume provided in the second
282                                 field. Please note that there is no protection
283                                 for the hidden volume if the outer volume is
284                                 mounted instead. See
285                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
286                                 for more information on this limitation.</para></listitem>
287                         </varlistentry>
288
289                         <varlistentry>
290                                 <term><option>tcrypt-keyfile=</option></term>
291
292                                 <listitem><para>Specifies the absolute path to a
293                                 key file to use for a TrueCrypt volume. This
294                                 implies <option>tcrypt</option> and can be
295                                 used more than once to provide several key
296                                 files.</para>
297
298                                 <para>See the entry for <option>tcrypt</option>
299                                 on the behavior of the passphrase and key files
300                                 when using TrueCrypt encryption mode.</para></listitem>
301                         </varlistentry>
302
303                         <varlistentry>
304                                 <term><option>tcrypt-system</option></term>
305
306                                 <listitem><para>Use TrueCrypt in system
307                                 encryption mode. This option implies
308                                 <option>tcrypt</option>.</para></listitem>
309                         </varlistentry>
310
311                         <varlistentry>
312                                 <term><option>timeout=</option></term>
313
314                                 <listitem><para>Specifies the timeout for
315                                 querying for a password. If no unit is
316                                 specified, seconds is used. Supported units are
317                                 s, ms, us, min, h, d. A timeout of 0 waits
318                                 indefinitely (which is the default).</para></listitem>
319                         </varlistentry>
320
321                         <varlistentry>
322                                 <term><option>x-systemd.device-timeout=</option></term>
323
324                                 <listitem><para>Specifies how long
325                                 systemd should wait for a device to
326                                 show up before giving up on the
327                                 entry. The argument is a time in
328                                 seconds or explicitly specifified
329                                 units of <literal>s</literal>,
330                                 <literal>min</literal>,
331                                 <literal>h</literal>,
332                                 <literal>ms</literal>.
333                                 </para></listitem>
334                         </varlistentry>
335
336                         <varlistentry>
337                                 <term><option>tmp</option></term>
338
339                                 <listitem><para>The encrypted block device will
340                                 be prepared for using it as <filename>/tmp</filename>;
341                                 it will be formatted using
342                                 <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
343                                 This option implies <option>plain</option>.</para>
344
345                                 <para>WARNING: Using the <option>tmp</option>
346                                 option will destroy the contents of the named
347                                 partition during every boot, so make sure the
348                                 underlying block device is specified correctly.</para></listitem>
349                         </varlistentry>
350
351                         <varlistentry>
352                                 <term><option>tries=</option></term>
353
354                                 <listitem><para>Specifies the maximum number of
355                                 times the user is queried for a password.
356                                 The default is 3. If set to 0, the user is
357                                 queried for a password indefinitely.</para></listitem>
358                         </varlistentry>
359
360                         <varlistentry>
361                                 <term><option>verify</option></term>
362
363                                 <listitem><para> If the encryption password is
364                                 read from console, it has to be entered twice to
365                                 prevent typos.</para></listitem>
366                         </varlistentry>
367
368                 </variablelist>
369
370                 <para>At early boot and when the system manager
371                 configuration is reloaded, this file is translated into
372                 native systemd units
373                 by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
374         </refsect1>
375
376         <refsect1>
377                 <title>Example</title>
378                 <example>
379                         <title>/etc/crypttab example</title>
380                         <para>Set up four encrypted block devices. One using
381                         LUKS for normal storage, another one for usage as a swap
382                         device and two TrueCrypt volumes.</para>
383
384                         <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
385 swap       /dev/sda7       /dev/urandom             swap
386 truecrypt  /dev/sda2       /etc/container_password  tcrypt
387 hidden     /mnt/tc_hidden  /dev/null                tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
388                 </example>
389         </refsect1>
390
391         <refsect1>
392                 <title>See Also</title>
393                 <para>
394                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
395                         <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
396                         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
397                         <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
398                         <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
399                         <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
400                 </para>
401         </refsect1>
402
403 </refentry>