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>header=</option></term>
 146
 147                                 <listitem><para>Use a detached (separated)
 148                                 metadata device or file where the LUKS header
 149                                 is stored. This option is only relevant for
 150                                 LUKS devices. See
 151                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 152                                 for possible values and the default value of
 153                                 this option.</para></listitem>
 154                         </varlistentry>
 155
 156                         <varlistentry>
 157                                 <term><option>keyfile-offset=</option></term>
 158
 159                                 <listitem><para>Specifies the number of bytes to
 160                                 skip at the start of the key file. See
 161                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 162                                 for possible values and the default value of
 163                                 this option.</para></listitem>
 164                         </varlistentry>
 165
 166                         <varlistentry>
 167                                 <term><option>keyfile-size=</option></term>
 168
 169                                 <listitem><para>Specifies the maximum number
 170                                 of bytes to read from the key file. See
 171                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 172                                 for possible values and the default value of
 173                                 this option. This option is ignored in plain
 174                                 encryption mode, as the key file size is then
 175                                 given by the key size.</para></listitem>
 176                         </varlistentry>
 177
 178                         <varlistentry>
 179                                 <term><option>key-slot=</option></term>
 180
 181                                 <listitem><para>Specifies the key slot to
 182                                 compare the passphrase or key against.
 183                                 If the key slot does not match the given
 184                                 passphrase or key, but another would, the
 185                                 setup of the device will fail regardless.
 186                                 This option implies <option>luks</option>. See
 187                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 188                                 for possible values. The default is to try
 189                                 all key slots in sequential order.</para></listitem>
 190                         </varlistentry>
 191
 192                         <varlistentry>
 193                                 <term><option>luks</option></term>
 194
 195                                 <listitem><para>Force LUKS mode. When this mode
 196                                 is used, the following options are ignored since
 197                                 they are provided by the LUKS header on the
 198                                 device: <option>cipher=</option>,
 199                                 <option>hash=</option>,
 200                                 <option>size=</option>.</para></listitem>
 201                         </varlistentry>
 202
 203                         <varlistentry>
 204                                 <term><option>noauto</option></term>
 205
 206                                 <listitem><para>This device will not be
 207                                 automatically unlocked on boot.</para></listitem>
 208                         </varlistentry>
 209
 210                         <varlistentry>
 211                                 <term><option>nofail</option></term>
 212
 213                                 <listitem><para>The system will not wait for the
 214                                 device to show up and be unlocked at boot, and
 215                                 not fail the boot if it does not show up.</para></listitem>
 216                         </varlistentry>
 217
 218                         <varlistentry>
 219                                 <term><option>plain</option></term>
 220
 221                                 <listitem><para>Force plain encryption mode.</para></listitem>
 222                         </varlistentry>
 223
 224                         <varlistentry>
 225                                 <term><option>read-only</option></term><term><option>readonly</option></term>
 226
 227                                 <listitem><para>Set up the encrypted block
 228                                 device in read-only mode.</para></listitem>
 229                         </varlistentry>
 230
 231                         <varlistentry>
 232                                 <term><option>size=</option></term>
 233
 234                                 <listitem><para>Specifies the key size
 235                                 in bits. See
 236                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 237                                 for possible values and the default value of
 238                                 this option.</para></listitem>
 239                         </varlistentry>
 240
 241                         <varlistentry>
 242                                 <term><option>swap</option></term>
 243
 244                                 <listitem><para>The encrypted block device will
 245                                 be used as a swap device, and will be formatted
 246                                 accordingly after setting up the encrypted
 247                                 block device, with
 248                                 <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 249                                 This option implies <option>plain</option>.</para>
 250
 251                                 <para>WARNING: Using the <option>swap</option>
 252                                 option will destroy the contents of the named
 253                                 partition during every boot, so make sure the
 254                                 underlying block device is specified correctly.</para></listitem>
 255                         </varlistentry>
 256
 257                         <varlistentry>
 258                                 <term><option>tcrypt</option></term>
 259
 260                                 <listitem><para>Use TrueCrypt encryption mode.
 261                                 When this mode is used, the following options are
 262                                 ignored since they are provided by the TrueCrypt
 263                                 header on the device or do not apply:
 264                                 <option>cipher=</option>,
 265                                 <option>hash=</option>,
 266                                 <option>keyfile-offset=</option>,
 267                                 <option>keyfile-size=</option>,
 268                                 <option>size=</option>.</para>
 269
 270                                 <para>When this mode is used, the passphrase is
 271                                 read from the key file given in the third field.
 272                                 Only the first line of this file is read,
 273                                 excluding the new line character.</para>
 274
 275                                 <para>Note that the TrueCrypt format uses both
 276                                 passphrase and key files to derive a password
 277                                 for the volume. Therefore, the passphrase and
 278                                 all key files need to be provided. Use
 279                                 <option>tcrypt-keyfile=</option> to provide
 280                                 the absolute path to all key files. When using
 281                                 an empty passphrase in combination with one or
 282                                 more key files, use <literal>/dev/null</literal>
 283                                 as the password file in the third field.</para></listitem>
 284                         </varlistentry>
 285
 286                         <varlistentry>
 287                                 <term><option>tcrypt-hidden</option></term>
 288
 289                                 <listitem><para>Use the hidden TrueCrypt volume.
 290                                 This option implies <option>tcrypt</option>.</para>
 291
 292                                 <para>This will map the hidden volume that is
 293                                 inside of the volume provided in the second
 294                                 field. Please note that there is no protection
 295                                 for the hidden volume if the outer volume is
 296                                 mounted instead. See
 297                                 <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 298                                 for more information on this limitation.</para></listitem>
 299                         </varlistentry>
 300
 301                         <varlistentry>
 302                                 <term><option>tcrypt-keyfile=</option></term>
 303
 304                                 <listitem><para>Specifies the absolute path to a
 305                                 key file to use for a TrueCrypt volume. This
 306                                 implies <option>tcrypt</option> and can be
 307                                 used more than once to provide several key
 308                                 files.</para>
 309
 310                                 <para>See the entry for <option>tcrypt</option>
 311                                 on the behavior of the passphrase and key files
 312                                 when using TrueCrypt encryption mode.</para></listitem>
 313                         </varlistentry>
 314
 315                         <varlistentry>
 316                                 <term><option>tcrypt-system</option></term>
 317
 318                                 <listitem><para>Use TrueCrypt in system
 319                                 encryption mode. This option implies
 320                                 <option>tcrypt</option>.</para></listitem>
 321                         </varlistentry>
 322
 323                         <varlistentry>
 324                                 <term><option>timeout=</option></term>
 325
 326                                 <listitem><para>Specifies the timeout for
 327                                 querying for a password. If no unit is
 328                                 specified, seconds is used. Supported units are
 329                                 s, ms, us, min, h, d. A timeout of 0 waits
 330                                 indefinitely (which is the default).</para></listitem>
 331                         </varlistentry>
 332
 333                         <varlistentry>
 334                                 <term><option>x-systemd.device-timeout=</option></term>
 335
 336                                 <listitem><para>Specifies how long
 337                                 systemd should wait for a device to
 338                                 show up before giving up on the
 339                                 entry. The argument is a time in
 340                                 seconds or explicitly specified
 341                                 units of <literal>s</literal>,
 342                                 <literal>min</literal>,
 343                                 <literal>h</literal>,
 344                                 <literal>ms</literal>.
 345                                 </para></listitem>
 346                         </varlistentry>
 347
 348                         <varlistentry>
 349                                 <term><option>tmp</option></term>
 350
 351                                 <listitem><para>The encrypted block device will
 352                                 be prepared for using it as <filename>/tmp</filename>;
 353                                 it will be formatted using
 354                                 <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 355                                 This option implies <option>plain</option>.</para>
 356
 357                                 <para>WARNING: Using the <option>tmp</option>
 358                                 option will destroy the contents of the named
 359                                 partition during every boot, so make sure the
 360                                 underlying block device is specified correctly.</para></listitem>
 361                         </varlistentry>
 362
 363                         <varlistentry>
 364                                 <term><option>tries=</option></term>
 365
 366                                 <listitem><para>Specifies the maximum number of
 367                                 times the user is queried for a password.
 368                                 The default is 3. If set to 0, the user is
 369                                 queried for a password indefinitely.</para></listitem>
 370                         </varlistentry>
 371
 372                         <varlistentry>
 373                                 <term><option>verify</option></term>
 374
 375                                 <listitem><para> If the encryption password is
 376                                 read from console, it has to be entered twice to
 377                                 prevent typos.</para></listitem>
 378                         </varlistentry>
 379
 380                 </variablelist>
 381
 382                 <para>At early boot and when the system manager
 383                 configuration is reloaded, this file is translated into
 384                 native systemd units
 385                 by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 386         </refsect1>
 387
 388         <refsect1>
 389                 <title>Example</title>
 390                 <example>
 391                         <title>/etc/crypttab example</title>
 392                         <para>Set up four encrypted block devices. One using
 393                         LUKS for normal storage, another one for usage as a swap
 394                         device and two TrueCrypt volumes.</para>
 395
 396                         <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
 397 swap       /dev/sda7       /dev/urandom             swap
 398 truecrypt  /dev/sda2       /etc/container_password  tcrypt
 399 hidden     /mnt/tc_hidden  /dev/null                tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
 400                 </example>
 401         </refsect1>
 402
 403         <refsect1>
 404                 <title>See Also</title>
 405                 <para>
 406                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 407                         <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 408                         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 409                         <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 410                         <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 411                         <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 412                 </para>
 413         </refsect1>
 414
 415 </refentry>