man/crypttab.xml

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   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
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  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>key-slot=</varname></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 implies <varname>luks</varname>. 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><varname>luks</varname></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: <varname>cipher=</varname>,
 187                                 <varname>hash=</varname>,
 188                                 <varname>size=</varname>.</para></listitem>
 189                         </varlistentry>
 190
 191                         <varlistentry>
 192                                 <term><varname>noauto</varname></term>
 193
 194                                 <listitem><para>This device will not be
 195                                 automatically unlocked on boot.</para></listitem>
 196                         </varlistentry>
 197
 198                         <varlistentry>
 199                                 <term><varname>nofail</varname></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><varname>plain</varname></term>
 208
 209                                 <listitem><para>Force plain encryption mode.</para></listitem>
 210                         </varlistentry>
 211
 212                         <varlistentry>
 213                                 <term><varname>read-only</varname></term><term><varname>readonly</varname></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><varname>size=</varname></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><varname>swap</varname></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><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 237                                 This option implies <varname>plain</varname>.</para>
 238
 239                                 <para>WARNING: Using the <varname>swap</varname>
 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><varname>tcrypt</varname></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                                 <varname>cipher=</varname>,
 253                                 <varname>hash=</varname>,
 254                                 <varname>keyfile-offset=</varname>,
 255                                 <varname>keyfile-size=</varname>,
 256                                 <varname>size=</varname>.</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                                 <varname>tcrypt-keyfile=</varname> 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><varname>tcrypt-hidden</varname></term>
 276
 277                                 <listitem><para>Use the hidden TrueCrypt volume.
 278                                 This implies <varname>tcrypt</varname>.</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><varname>tcrypt-keyfile=</varname></term>
 291
 292                                 <listitem><para>Specifies the absolute path to a
 293                                 key file to use for a TrueCrypt volume. This
 294                                 implies <varname>tcrypt</varname> and can be
 295                                 used more than once to provide several key
 296                                 files.</para>
 297
 298                                 <para>See the entry for <varname>tcrypt</varname>
 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><varname>tcrypt-system</varname></term>
 305
 306                                 <listitem><para>Use TrueCrypt in system
 307                                 encryption mode. This implies
 308                                 <varname>tcrypt</varname>.</para>
 309
 310                                 <para>Please note that when using this mode, the
 311                                 whole device needs to be given in the second
 312                                 field instead of the partition. For example: if
 313                                 <literal>/dev/sda2</literal> is the system
 314                                 encrypted TrueCrypt patition, <literal>/dev/sda</literal>
 315                                 has to be given.</para></listitem>
 316                         </varlistentry>
 317
 318                         <varlistentry>
 319                                 <term><varname>timeout=</varname></term>
 320
 321                                 <listitem><para>Specifies the timeout for
 322                                 querying for a password. If no unit is
 323                                 specified, seconds is used. Supported units are
 324                                 s, ms, us, min, h, d. A timeout of 0 waits
 325                                 indefinitely (which is the default).</para></listitem>
 326                         </varlistentry>
 327
 328                         <varlistentry>
 329                                 <term><varname>tmp</varname></term>
 330
 331                                 <listitem><para>The encrypted block device will
 332                                 be prepared for using it as <filename>/tmp</filename>;
 333                                 it will be formatted using
 334                                 <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 335                                 This option implies <varname>plain</varname>.</para>
 336
 337                                 <para>WARNING: Using the <varname>tmp</varname>
 338                                 option will destroy the contents of the named
 339                                 partition during every boot, so make sure the
 340                                 underlying block device is specified correctly.</para></listitem>
 341                         </varlistentry>
 342
 343                         <varlistentry>
 344                                 <term><varname>tries=</varname></term>
 345
 346                                 <listitem><para>Specifies the maximum number of
 347                                 times the user is queried for a password.
 348                                 The default is 3. If set to 0, the user is
 349                                 queried for a password indefinitely.</para></listitem>
 350                         </varlistentry>
 351
 352                         <varlistentry>
 353                                 <term><varname>verify</varname></term>
 354
 355                                 <listitem><para> If the encryption password is
 356                                 read from console, it has to be entered twice to
 357                                 prevent typos.</para></listitem>
 358                         </varlistentry>
 359
 360                 </variablelist>
 361
 362                 <para>At early boot and when the system manager
 363                 configuration is reloaded, this file is translated into
 364                 native systemd units
 365                 by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 366         </refsect1>
 367
 368         <refsect1>
 369                 <title>Example</title>
 370                 <example>
 371                         <title>/etc/crypttab example</title>
 372                         <para>Set up four encrypted block devices. One using
 373                         LUKS for normal storage, another one for usage as a swap
 374                         device and two TrueCrypt volumes.</para>
 375
 376                         <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
 377 swap       /dev/sda7       /dev/urandom             swap
 378 truecrypt  /dev/sda2       /etc/container_password  tcrypt
 379 hidden     /mnt/tc_hidden  /null                    tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
 380                 </example>
 381         </refsect1>
 382
 383         <refsect1>
 384                 <title>See Also</title>
 385                 <para>
 386                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 387                         <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 388                         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 389                         <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 390                         <citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 391                         <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 392                 </para>
 393         </refsect1>
 394
 395 </refentry>