man/crypttab.xml

   1 <?xml version="1.0"?>
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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
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  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>allow-discards</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.</para></listitem>
 334                         </varlistentry>
 335
 336                         <varlistentry>
 337                                 <term><varname>verify</varname></term>
 338
 339                                 <listitem><para> If the encryption password is
 340                                 read from console, it has to be entered twice to
 341                                 prevent typos.</para></listitem>
 342                         </varlistentry>
 343
 344                 </variablelist>
 345
 346                 <para>At early boot and when the system manager
 347                 configuration is reloaded, this file is translated into
 348                 native systemd units
 349                 by <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 350         </refsect1>
 351
 352         <refsect1>
 353                 <title>Example</title>
 354                 <example>
 355                         <title>/etc/crypttab example</title>
 356                         <para>Set up four encrypted block devices. One using
 357                         LUKS for normal storage, another one for usage as a swap
 358                         device and two TrueCrypt volumes.</para>
 359
 360                         <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
 361 swap       /dev/sda7       /dev/urandom             swap
 362 truecrypt  /dev/sda2       /etc/container_password  tcrypt
 363 hidden     /mnt/tc_hidden  /null                    tcrypt-hidden,tcrypt-keyfile=/etc/keyfile</programlisting>
 364                 </example>
 365         </refsect1>
 366
 367         <refsect1>
 368                 <title>See Also</title>
 369                 <para>
 370                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 371                         <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 372                         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 373                         <citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 374                         <citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 375                         <citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 376                 </para>
 377         </refsect1>
 378
 379 </refentry>