man/crypttab.xml

   1 <?xml version="1.0"?>
   2 <!--*-nxml-*-->
   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   4   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1-or-later
   7
   8   This is based on crypttab(5) from Fedora's initscripts package, which in
   9   turn is based on Debian's version.
  10
  11   The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
  12 -->
  13 <refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP' xmlns:xi="http://www.w3.org/2001/XInclude">
  14
  15   <refentryinfo>
  16     <title>crypttab</title>
  17     <productname>systemd</productname>
  18   </refentryinfo>
  19
  20   <refmeta>
  21     <refentrytitle>crypttab</refentrytitle>
  22     <manvolnum>5</manvolnum>
  23   </refmeta>
  24
  25   <refnamediv>
  26     <refname>crypttab</refname>
  27     <refpurpose>Configuration for encrypted block devices</refpurpose>
  28   </refnamediv>
  29
  30   <refsynopsisdiv>
  31     <para><filename>/etc/crypttab</filename></para>
  32   </refsynopsisdiv>
  33
  34   <refsect1>
  35     <title>Description</title>
  36
  37     <para>The <filename>/etc/crypttab</filename> file describes
  38     encrypted block devices that are set up during system boot.</para>
  39
  40     <para>Empty lines and lines starting with the <literal>#</literal>
  41     character are ignored. Each of the remaining lines describes one
  42     encrypted block device. Fields are delimited by white space.</para>
  43
  44     <para>Each line is in the form<programlisting><replaceable>volume-name</replaceable> <replaceable>encrypted-device</replaceable> <replaceable>key-file</replaceable> <replaceable>options</replaceable></programlisting>
  45     The first two fields are mandatory, the remaining two are
  46     optional.</para>
  47
  48     <para>Setting up encrypted block devices using this file supports four encryption modes: LUKS, TrueCrypt,
  49     BitLocker and plain. See <citerefentry
  50     project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
  51     more information about each mode. When no mode is specified in the options field and the block device
  52     contains a LUKS signature, it is opened as a LUKS device; otherwise, it is assumed to be in raw dm-crypt
  53     (plain mode) format.</para>
  54
  55     <para>The four fields of <filename>/etc/crypttab</filename> are defined as follows:</para>
  56
  57     <orderedlist>
  58
  59       <listitem><para>The first field contains the name of the resulting volume with decrypted data; its
  60       block device is set up below <filename>/dev/mapper/</filename>.</para></listitem>
  61
  62       <listitem><para>The second field contains a path to the underlying block
  63       device or file, or a specification of a block device via
  64       <literal>UUID=</literal> followed by the UUID.</para></listitem>
  65
  66       <listitem><para>The third field specifies an absolute path to a file with the encryption
  67       key. Optionally, the path may be followed by <literal>:</literal> and an
  68       <filename>/etc/fstab</filename> style device specification (e.g. starting with
  69       <literal>LABEL=</literal> or similar); in which case the path is taken relative to the specified
  70       device's file system root. If the field is not present or is <literal>none</literal> or
  71       <literal>-</literal>, a key file named after the volume to unlock (i.e. the first column of the line),
  72       suffixed with <filename>.key</filename> is automatically loaded from the
  73       <filename>/etc/cryptsetup-keys.d/</filename> and <filename>/run/cryptsetup-keys.d/</filename>
  74       directories, if present. Otherwise, the password has to be manually entered during system boot. For
  75       swap encryption, <filename>/dev/urandom</filename> may be used as key file, resulting in a randomized
  76       key.</para>
  77
  78       <para>If the specified key file path refers to an <constant>AF_UNIX</constant> stream socket in the
  79       file system, the key is acquired by connecting to the socket and reading it from the connection. This
  80       allows the implementation of a service to provide key information dynamically, at the moment when it is
  81       needed. For details see below.</para></listitem>
  82
  83       <listitem><para>The fourth field, if present, is a comma-delimited list of options. The supported
  84       options are listed below.</para></listitem>
  85     </orderedlist>
  86   </refsect1>
  87
  88   <refsect1>
  89     <title>Key Acquisition</title>
  90
  91     <para>Six different mechanisms for acquiring the decryption key or passphrase unlocking the encrypted
  92     volume are supported. Specifically:</para>
  93
  94     <orderedlist>
  95
  96       <listitem><para>Most prominently, the user may be queried interactively during volume activation
  97       (i.e. typically at boot), asking them to type in the necessary passphrases.</para></listitem>
  98
  99       <listitem><para>The (unencrypted) key may be read from a file on disk, possibly on removable media. The third field
 100       of each line encodes the location, for details see above.</para></listitem>
 101
 102       <listitem><para>The (unencrypted) key may be requested from another service, by specifying an
 103       <constant>AF_UNIX</constant> file system socket in place of a key file in the third field. For details
 104       see above and below.</para></listitem>
 105
 106       <listitem><para>The key may be acquired via a PKCS#11 compatible hardware security token or
 107       smartcard. In this case a saved key used in unlock process is stored on disk/removable media, acquired via
 108       <constant>AF_UNIX</constant>, or stored in the LUKS2 JSON token metadata header. For RSA, the saved key
 109       is an encrypted volume key. The encrypted volume key is then decrypted by the PKCS#11 token with an RSA
 110       private key stored on it, and used to unlock the encrypted volume. For elliptic-curve (EC) cryptography,
 111       the saved key is the public key generated in enrollment process. The public key is then used to derive
 112       a shared secret with a private key stored in the PKCS#11 token. The derived shared secret is then used
 113       to unlock the volume. Use the <option>pkcs11-uri=</option> option described below to use this mechanism.
 114       </para></listitem>
 115
 116       <listitem><para>Similarly, the key may be acquired via a FIDO2 compatible hardware security token
 117       (which must implement the "hmac-secret" extension). In this case a key generated randomly during
 118       enrollment is stored on disk/removable media, acquired via <constant>AF_UNIX</constant>, or stored in
 119       the LUKS2 JSON token metadata header. The random key is hashed via a keyed hash function (HMAC) on the
 120       FIDO2 token, using a secret key stored on the token that never leaves it. The resulting hash value is
 121       then used as key to unlock the encrypted volume. Use the <option>fido2-device=</option> option
 122       described below to use this mechanism.</para></listitem>
 123
 124       <listitem><para>Similarly, the key may be acquired via a TPM2 security chip. In this case a (during
 125       enrollment) randomly generated key — encrypted by an asymmetric key derived from the TPM2 chip's seed
 126       key — is stored on disk/removable media, acquired via <constant>AF_UNIX</constant>, or stored in the
 127       LUKS2 JSON token metadata header. Use the <option>tpm2-device=</option> option described below to use
 128       this mechanism.</para></listitem>
 129     </orderedlist>
 130
 131     <para>For the latter five mechanisms the source for the key material used for unlocking the volume is
 132     primarily configured in the third field of each <filename>/etc/crypttab</filename> line, but may also
 133     be configured in <filename>/etc/cryptsetup-keys.d/</filename> and
 134     <filename>/run/cryptsetup-keys.d/</filename> (see above) or in the LUKS2 JSON token header (in case of
 135     the latter three). Use the
 136     <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 137     tool to enroll PKCS#11, FIDO2 and TPM2 devices in LUKS2 volumes.</para>
 138   </refsect1>
 139
 140   <refsect1>
 141     <title>Supported Options</title>
 142
 143     <para>The following options may be used in the fourth field of each line:</para>
 144
 145     <variablelist class='fstab-options'>
 146
 147       <varlistentry>
 148         <term><option>cipher=</option></term>
 149
 150         <listitem><para>Specifies the cipher to use. See <citerefentry
 151         project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 152         for possible values and the default value of this option. A cipher with unpredictable IV values, such
 153         as <literal>aes-cbc-essiv:sha256</literal>, is recommended. Embedded commas in the cipher
 154         specification need to be escaped by preceding them with a backslash, see example below.</para>
 155
 156         <xi:include href="version-info.xml" xpointer="v186"/>
 157         </listitem>
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term><option>discard</option></term>
 162
 163         <listitem><para>Allow discard requests to be passed through the encrypted block
 164         device. This improves performance on SSD storage but has security implications.
 165         </para>
 166
 167         <xi:include href="version-info.xml" xpointer="v207"/></listitem>
 168       </varlistentry>
 169
 170       <varlistentry>
 171         <term><option>hash=</option></term>
 172
 173         <listitem><para>Specifies the hash to use for password
 174         hashing. See
 175         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 176         for possible values and the default value of this
 177         option.</para>
 178
 179         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 180       </varlistentry>
 181
 182       <varlistentry>
 183         <term><option>header=</option></term>
 184
 185         <listitem><para>Use a detached (separated) metadata device or file
 186         where the header containing the master key(s) is stored. This
 187         option is only relevant for LUKS and TrueCrypt/VeraCrypt devices. See
 188         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 189         for possible values and the default value of this option.</para>
 190
 191         <para>Optionally, the path may be followed by <literal>:</literal> and an
 192         <filename>/etc/fstab</filename> device specification (e.g. starting with <literal>UUID=</literal> or
 193         similar); in which case, the path is relative to the device file system root. The device gets mounted
 194         automatically for LUKS device activation duration only.</para>
 195
 196         <xi:include href="version-info.xml" xpointer="v219"/></listitem>
 197       </varlistentry>
 198
 199       <varlistentry>
 200         <term><option>keyfile-offset=</option></term>
 201
 202         <listitem><para>Specifies the number of bytes to skip at the
 203         start of the key file. See
 204         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 205         for possible values and the default value of this
 206         option.</para>
 207
 208         <xi:include href="version-info.xml" xpointer="v187"/></listitem>
 209       </varlistentry>
 210
 211       <varlistentry>
 212         <term><option>keyfile-size=</option></term>
 213
 214         <listitem><para>Specifies the maximum number of bytes to read
 215         from the key file. See
 216         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 217         for possible values and the default value of this option. This
 218         option is ignored in plain encryption mode, as the key file
 219         size is then given by the key size.</para>
 220
 221         <xi:include href="version-info.xml" xpointer="v188"/></listitem>
 222       </varlistentry>
 223
 224       <varlistentry>
 225         <term><option>keyfile-erase</option></term>
 226
 227         <listitem><para>If enabled, the specified key file is erased after the volume is activated or when
 228         activation fails. This is in particular useful when the key file is only acquired transiently before
 229         activation (e.g. via a file in <filename>/run/</filename>, generated by a service running before
 230         activation), and shall be removed after use. Defaults to off.</para>
 231
 232         <xi:include href="version-info.xml" xpointer="v246"/></listitem>
 233       </varlistentry>
 234
 235       <varlistentry>
 236         <term><option>key-slot=</option></term>
 237
 238         <listitem><para>Specifies the key slot to compare the
 239         passphrase or key against. If the key slot does not match the
 240         given passphrase or key, but another would, the setup of the
 241         device will fail regardless. This option implies
 242         <option>luks</option>. See
 243         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 244         for possible values. The default is to try all key slots in
 245         sequential order.</para>
 246
 247         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 248       </varlistentry>
 249
 250       <varlistentry>
 251         <term><option>keyfile-timeout=</option></term>
 252
 253         <listitem><para> Specifies the timeout for the device on
 254         which the key file resides or the device used as the key file,
 255         and falls back to a password if it could not be accessed. See
 256         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 257         for key files on external devices.
 258         </para>
 259
 260         <xi:include href="version-info.xml" xpointer="v243"/></listitem>
 261       </varlistentry>
 262
 263       <varlistentry>
 264         <term><option>link-volume-key=</option></term>
 265
 266         <listitem><para>Specifies the kernel keyring and key description
 267         (see <citerefentry project='man-pages'><refentrytitle>keyrings</refentrytitle><manvolnum>7</manvolnum></citerefentry>)
 268         where LUKS2 volume key gets linked during device activation. The kernel keyring
 269         description and key description must be separated by <literal>::</literal>.</para>
 270
 271         <para>The kernel keyring part can be a string description or a predefined
 272         kernel keyring prefixed with <literal>@</literal> (e.g.: to use <literal>@s</literal> session or
 273         <literal>@u</literal> user keyring directly). The type prefix text in the kernel keyring description
 274         is not required. The specified kernel keyring must already exist at the time of device activation.</para>
 275
 276         <para>The key part is a string description optionally prefixed by a <literal>%key_type:</literal>.
 277         If no type is specified, the <literal>user</literal> type key is linked by default. See
 278         <citerefentry project='man-pages'><refentrytitle>keyctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 279         for more information on key descriptions (KEY IDENTIFIERS section).</para>
 280
 281         <para>Note that the linked volume key is not cleaned up automatically when the device is detached.</para>
 282
 283         <xi:include href="version-info.xml" xpointer="v256"/></listitem>
 284       </varlistentry>
 285
 286       <varlistentry>
 287         <term><option>luks</option></term>
 288
 289         <listitem><para>Force LUKS mode. When this mode is used, the
 290         following options are ignored since they are provided by the
 291         LUKS header on the device: <option>cipher=</option>,
 292         <option>hash=</option>,
 293         <option>size=</option>.</para>
 294
 295         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 296       </varlistentry>
 297
 298       <varlistentry>
 299         <term><option>bitlk</option></term>
 300
 301         <listitem><para>Decrypt BitLocker drive. Encryption parameters
 302         are deduced by cryptsetup from BitLocker header.</para>
 303
 304         <xi:include href="version-info.xml" xpointer="v246"/></listitem>
 305       </varlistentry>
 306
 307       <varlistentry>
 308         <term><option>_netdev</option></term>
 309
 310         <listitem><para>Marks this cryptsetup device as requiring network. It will be
 311         started after the network is available, similarly to
 312         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 313         units marked with <option>_netdev</option>. The service unit to set up this device
 314         will be ordered between <filename>remote-fs-pre.target</filename> and
 315         <filename>remote-cryptsetup.target</filename>, instead of
 316         <filename>cryptsetup-pre.target</filename> and
 317         <filename>cryptsetup.target</filename>.</para>
 318
 319         <para>Hint: if this device is used for a mount point that is specified in
 320         <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 321         the <option>_netdev</option> option should also be used for the mount
 322         point. Otherwise, a dependency loop might be created where the mount point
 323         will be pulled in by <filename>local-fs.target</filename>, while the
 324         service to configure the network is usually only started <emphasis>after</emphasis>
 325         the local file system has been mounted.</para>
 326
 327         <xi:include href="version-info.xml" xpointer="v235"/>
 328         </listitem>
 329       </varlistentry>
 330
 331       <varlistentry>
 332         <term><option>noauto</option></term>
 333
 334         <listitem><para>This device will not be added to <filename>cryptsetup.target</filename>.
 335         This means that it will not be automatically unlocked on boot, unless something else pulls
 336         it in. In particular, if the device is used for a mount point, it'll be unlocked
 337         automatically during boot, unless the mount point itself is also disabled with
 338         <option>noauto</option>.</para>
 339
 340         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 341       </varlistentry>
 342
 343       <varlistentry>
 344         <term><option>nofail</option></term>
 345
 346         <listitem><para>This device will not be a hard dependency of
 347         <filename>cryptsetup.target</filename>. It'll still be pulled in and started, but the system
 348         will not wait for the device to show up and be unlocked, and boot will not fail if this is
 349         unsuccessful. Note that other units that depend on the unlocked device may still fail. In
 350         particular, if the device is used for a mount point, the mount point itself also needs to
 351         have the <option>nofail</option> option, or the boot will fail if the device is not unlocked
 352         successfully. If a keyfile and/or a <option>header</option> are specified, the dependencies on
 353         their respective directories will also not be fatal, so that umounting said directories will
 354         not cause the generated cryptset unit to be deactivated.</para>
 355
 356         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 357       </varlistentry>
 358
 359       <varlistentry>
 360         <term><option>offset=</option></term>
 361
 362         <listitem><para>Start offset in the backend device, in 512-byte sectors. This
 363         option is only relevant for plain devices.</para>
 364
 365         <xi:include href="version-info.xml" xpointer="v220"/></listitem>
 366       </varlistentry>
 367
 368       <varlistentry>
 369         <term><option>plain</option></term>
 370
 371         <listitem><para>Force plain encryption mode.</para>
 372
 373         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 374       </varlistentry>
 375
 376       <varlistentry>
 377         <term><option>read-only</option></term><term><option>readonly</option></term>
 378
 379         <listitem><para>Set up the encrypted block device in read-only
 380         mode.</para>
 381
 382         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 383       </varlistentry>
 384
 385       <varlistentry>
 386         <term><option>same-cpu-crypt</option></term>
 387
 388         <listitem><para>Perform encryption using the same CPU that IO was submitted on. The default is to use
 389         an unbound workqueue so that encryption work is automatically balanced between available CPUs.</para>
 390
 391         <para>This requires kernel 4.0 or newer.</para>
 392
 393         <xi:include href="version-info.xml" xpointer="v242"/>
 394         </listitem>
 395       </varlistentry>
 396
 397       <varlistentry>
 398         <term><option>submit-from-crypt-cpus</option></term>
 399
 400         <listitem><para>Disable offloading writes to a separate thread after encryption. There are some
 401         situations where offloading write requests from the encryption threads to a dedicated thread degrades
 402         performance significantly. The default is to offload write requests to a dedicated thread because it
 403         benefits the CFQ scheduler to have writes submitted using the same context.</para>
 404
 405         <para>This requires kernel 4.0 or newer.</para>
 406
 407         <xi:include href="version-info.xml" xpointer="v242"/>
 408         </listitem>
 409       </varlistentry>
 410
 411       <varlistentry>
 412         <term><option>no-read-workqueue</option></term>
 413
 414         <listitem><para>Bypass dm-crypt internal workqueue and process read requests synchronously. The
 415         default is to queue these requests and process them asynchronously.</para>
 416
 417         <para>This requires kernel 5.9 or newer.</para>
 418
 419         <xi:include href="version-info.xml" xpointer="v248"/>
 420         </listitem>
 421       </varlistentry>
 422       <varlistentry>
 423         <term><option>no-write-workqueue</option></term>
 424
 425         <listitem><para>Bypass dm-crypt internal workqueue and process write requests synchronously. The
 426         default is to queue these requests and process them asynchronously.</para>
 427
 428         <para>This requires kernel 5.9 or newer.</para>
 429
 430         <xi:include href="version-info.xml" xpointer="v248"/>
 431         </listitem>
 432       </varlistentry>
 433
 434       <varlistentry>
 435         <term><option>skip=</option></term>
 436
 437         <listitem><para>How many 512-byte sectors of the encrypted data to skip at the
 438         beginning. This is different from the <option>offset=</option> option with respect
 439         to the sector numbers used in initialization vector (IV) calculation. Using
 440         <option>offset=</option> will shift the IV calculation by the same negative
 441         amount. Hence, if <option>offset=<replaceable>n</replaceable></option> is given,
 442         sector <replaceable>n</replaceable> will get a sector number of 0 for the IV
 443         calculation. Using <option>skip=</option> causes sector
 444         <replaceable>n</replaceable> to also be the first sector of the mapped device, but
 445         with its number for IV generation being <replaceable>n</replaceable>.</para>
 446
 447         <para>This option is only relevant for plain devices.</para>
 448
 449         <xi:include href="version-info.xml" xpointer="v220"/>
 450         </listitem>
 451       </varlistentry>
 452
 453       <varlistentry>
 454         <term><option>size=</option></term>
 455
 456         <listitem><para>Specifies the key size in bits. See
 457         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 458         for possible values and the default value of this
 459         option.</para>
 460
 461         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 462       </varlistentry>
 463
 464       <varlistentry>
 465         <term><option>sector-size=</option></term>
 466
 467         <listitem><para>Specifies the sector size in bytes. See
 468         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 469         for possible values and the default value of this
 470         option.</para>
 471
 472         <xi:include href="version-info.xml" xpointer="v240"/></listitem>
 473       </varlistentry>
 474
 475       <varlistentry>
 476         <term><option>swap</option></term>
 477
 478         <listitem><para>The encrypted block device will be used as a
 479         swap device, and will be formatted accordingly after setting
 480         up the encrypted block device, with
 481         <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 482         This option implies <option>plain</option>.</para>
 483
 484         <warning>
 485           <para>Using the <option>swap</option> option will
 486           destroy the contents of the named partition during every boot,
 487           so make sure the underlying block device is specified
 488           correctly.</para>
 489         </warning>
 490
 491         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 492       </varlistentry>
 493
 494       <varlistentry>
 495         <term><option>tcrypt</option></term>
 496
 497         <listitem><para>Use TrueCrypt encryption mode. When this mode
 498         is used, the following options are ignored since they are
 499         provided by the TrueCrypt header on the device or do not
 500         apply:
 501         <option>cipher=</option>,
 502         <option>hash=</option>,
 503         <option>keyfile-offset=</option>,
 504         <option>keyfile-size=</option>,
 505         <option>size=</option>.</para>
 506
 507         <para>When this mode is used, the passphrase is read from the
 508         key file given in the third field. Only the first line of this
 509         file is read, excluding the new line character.</para>
 510
 511         <para>Note that the TrueCrypt format uses both passphrase and
 512         key files to derive a password for the volume. Therefore, the
 513         passphrase and all key files need to be provided. Use
 514         <option>tcrypt-keyfile=</option> to provide the absolute path
 515         to all key files. When using an empty passphrase in
 516         combination with one or more key files, use
 517         <literal>/dev/null</literal> as the password file in the third
 518         field.</para>
 519
 520         <xi:include href="version-info.xml" xpointer="v206"/></listitem>
 521       </varlistentry>
 522
 523       <varlistentry>
 524         <term><option>tcrypt-hidden</option></term>
 525
 526         <listitem><para>Use the hidden TrueCrypt volume. This option
 527         implies <option>tcrypt</option>.</para>
 528
 529         <para>This will map the hidden volume that is inside of the
 530         volume provided in the second field. Please note that there is
 531         no protection for the hidden volume if the outer volume is
 532         mounted instead. See
 533         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 534         for more information on this limitation.</para>
 535
 536         <xi:include href="version-info.xml" xpointer="v206"/></listitem>
 537       </varlistentry>
 538
 539       <varlistentry>
 540         <term><option>tcrypt-keyfile=</option></term>
 541
 542         <listitem><para>Specifies the absolute path to a key file to
 543         use for a TrueCrypt volume. This implies
 544         <option>tcrypt</option> and can be used more than once to
 545         provide several key files.</para>
 546
 547         <para>See the entry for <option>tcrypt</option> on the
 548         behavior of the passphrase and key files when using TrueCrypt
 549         encryption mode.</para>
 550
 551         <xi:include href="version-info.xml" xpointer="v206"/></listitem>
 552       </varlistentry>
 553
 554       <varlistentry>
 555         <term><option>tcrypt-system</option></term>
 556
 557         <listitem><para>Use TrueCrypt in system encryption mode. This
 558         option implies <option>tcrypt</option>.</para>
 559
 560         <xi:include href="version-info.xml" xpointer="v206"/></listitem>
 561       </varlistentry>
 562
 563       <varlistentry>
 564         <term><option>tcrypt-veracrypt</option></term>
 565
 566         <listitem><para>Check for a VeraCrypt volume.  VeraCrypt is a fork of
 567         TrueCrypt that is mostly compatible, but uses different, stronger key
 568         derivation algorithms that cannot be detected without this flag.
 569         Enabling this option could substantially slow down unlocking, because
 570         VeraCrypt's key derivation takes much longer than TrueCrypt's.  This
 571         option implies <option>tcrypt</option>.</para>
 572
 573         <xi:include href="version-info.xml" xpointer="v232"/></listitem>
 574       </varlistentry>
 575
 576       <varlistentry>
 577         <term><option>veracrypt-pim=</option></term>
 578
 579         <listitem><para>Specifies a custom Personal Iteration Multiplier (PIM)
 580         value, which can range from 0..2147468 for standard veracrypt volumes
 581         and 0..65535 for veracrypt system volumes. A value of 0 will imply the
 582         VeraCrypt default.
 583
 584         This option is only effective when <option>tcrypt-veracrypt</option> is
 585         set.</para>
 586
 587         <para>Note that VeraCrypt enforces a minimal allowed PIM value depending on the
 588         password strength and the hash algorithm used for key derivation, however
 589         <option>veracrypt-pim=</option> is not checked against these bounds.
 590         See
 591         <ulink url="https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html">Veracrypt Personal Iterations Multiplier</ulink>
 592         documentation for more information.</para>
 593
 594         <xi:include href="version-info.xml" xpointer="v254"/>
 595         </listitem>
 596       </varlistentry>
 597
 598       <varlistentry>
 599         <term><option>timeout=</option></term>
 600
 601         <listitem><para>Specifies the timeout for querying for a
 602         password. If no unit is specified, seconds is used. Supported
 603         units are s, ms, us, min, h, d. A timeout of 0 waits
 604         indefinitely (which is the default).</para>
 605
 606         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 607       </varlistentry>
 608
 609       <varlistentry>
 610         <term><option>tmp=</option></term>
 611
 612         <listitem><para>The encrypted block device will be prepared for using it as
 613         <filename>/tmp/</filename>; it will be formatted using <citerefentry
 614         project='man-pages'><refentrytitle>mkfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes
 615         a file system type as argument, such as <literal>ext4</literal>, <literal>xfs</literal> or
 616         <literal>btrfs</literal>. If no argument is specified defaults to <literal>ext4</literal>. This
 617         option implies <option>plain</option>.</para>
 618
 619         <warning>
 620           <para>Using the <option>tmp</option> option will destroy the contents of the named partition
 621           during every boot, so make sure the underlying block device is specified correctly.</para>
 622         </warning>
 623
 624         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 625       </varlistentry>
 626
 627       <varlistentry>
 628         <term><option>tries=</option></term>
 629
 630         <listitem><para>Specifies the maximum number of times the user
 631         is queried for a password. The default is 3. If set to 0, the
 632         user is queried for a password indefinitely.</para>
 633
 634         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 635       </varlistentry>
 636
 637       <varlistentry>
 638         <term><option>headless=</option></term>
 639
 640         <listitem><para>Takes a boolean argument, defaults to false. If true, never query interactively
 641         for the password/PIN. Useful for headless systems.</para>
 642
 643         <xi:include href="version-info.xml" xpointer="v249"/></listitem>
 644       </varlistentry>
 645
 646       <varlistentry>
 647         <term><option>verify</option></term>
 648
 649         <listitem><para>If the encryption password is read from console, it has to be entered twice to
 650         prevent typos.</para>
 651
 652         <xi:include href="version-info.xml" xpointer="v186"/></listitem>
 653       </varlistentry>
 654
 655       <varlistentry>
 656         <term><option>password-echo=yes|no|masked</option></term>
 657
 658         <listitem><para>Controls whether to echo passwords or security token PINs
 659         that are read from console. Takes a boolean or the special string <literal>masked</literal>.
 660         The default is <option>password-echo=masked</option>.</para>
 661
 662         <para>If enabled, the typed characters are echoed literally. If disabled,
 663         the typed characters are not echoed in any form, the user will not get
 664         feedback on their input. If set to <literal>masked</literal>, an asterisk
 665         (<literal>*</literal>) is echoed for each character typed. Regardless of
 666         which mode is chosen, if the user hits the tabulator key (<literal>↹</literal>)
 667         at any time, or the backspace key (<literal>⌫</literal>) before any other
 668         data has been entered, then echo is turned off.</para>
 669
 670         <xi:include href="version-info.xml" xpointer="v249"/></listitem>
 671       </varlistentry>
 672
 673       <varlistentry>
 674         <term><option>pkcs11-uri=</option></term>
 675
 676         <listitem><para>Takes either the special value <literal>auto</literal> or an <ulink
 677         url="https://tools.ietf.org/html/rfc7512">RFC7512 PKCS#11 URI</ulink> pointing to a private key
 678         which is used to decrypt the encrypted key specified in the third column of the line. This is useful
 679         for unlocking encrypted volumes through PKCS#11 compatible security tokens or smartcards. See below
 680         for an example how to set up this mechanism for unlocking a LUKS2 volume with a YubiKey security
 681         token.</para>
 682
 683         <para>If specified as <literal>auto</literal> the volume must be of type LUKS2 and must carry PKCS#11
 684         security token metadata in its LUKS2 JSON token section. In this mode the URI and the encrypted key
 685         are automatically read from the LUKS2 JSON token header. Use
 686         <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 687         as a simple tool for enrolling PKCS#11 security tokens or smartcards in a way compatible with
 688         <literal>auto</literal>. In this mode the third column of the line should remain empty (that is,
 689         specified as <literal>-</literal>).</para>
 690
 691         <para>The specified URI can refer directly to a private key stored on a token or alternatively
 692         just to a slot or token, in which case a search for a suitable private key will be performed.  In
 693         this case if multiple suitable objects are found the token is refused. The keyfile configured
 694         in the third column of the line is used as is (i.e. in binary form, unprocessed). The resulting
 695         decrypted key (for RSA) or derived shared secret (for ECC) is then Base64 encoded before it is used
 696         to unlock the LUKS volume.</para>
 697
 698         <para>Use <command>systemd-cryptenroll --pkcs11-token-uri=list</command> to list all suitable PKCS#11
 699         security tokens currently plugged in, along with their URIs.</para>
 700
 701         <para>Note that many newer security tokens that may be used as PKCS#11 security token typically also
 702         implement the newer and simpler FIDO2 standard. Consider using <option>fido2-device=</option>
 703         (described below) to enroll it via FIDO2 instead. Note that a security token enrolled via PKCS#11
 704         cannot be used to unlock the volume via FIDO2, unless also enrolled via FIDO2, and vice
 705         versa.</para>
 706
 707         <xi:include href="version-info.xml" xpointer="v245"/></listitem>
 708       </varlistentry>
 709
 710       <varlistentry>
 711         <term><option>fido2-device=</option></term>
 712
 713         <listitem><para>Takes either the special value <literal>auto</literal> or the path to a
 714         <literal>hidraw</literal> device node (e.g. <filename>/dev/hidraw1</filename>) referring to a FIDO2
 715         security token that implements the <literal>hmac-secret</literal> extension (most current hardware
 716         security tokens do). See below for an example how to set up this mechanism for unlocking an encrypted
 717         volume with a FIDO2 security token.</para>
 718
 719         <para>If specified as <literal>auto</literal> the FIDO2 token device is automatically discovered, as
 720         it is plugged in.</para>
 721
 722         <para>FIDO2 volume unlocking requires a client ID hash (CID) to be configured via
 723         <option>fido2-cid=</option> (see below) and a key to pass to the security token's HMAC functionality
 724         (configured in the line's third column) to operate. If not configured and the volume is of type
 725         LUKS2, the CID and the key are read from LUKS2 JSON token metadata instead. Use
 726         <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 727         as simple tool for enrolling FIDO2 security tokens, compatible with this automatic mode, which is
 728         only available for LUKS2 volumes.</para>
 729
 730         <para>Use <command>systemd-cryptenroll --fido2-device=list</command> to list all suitable FIDO2
 731         security tokens currently plugged in, along with their device nodes.</para>
 732
 733         <para>This option implements the following mechanism: the configured key is hashed via they HMAC
 734         keyed hash function the FIDO2 device implements, keyed by a secret key embedded on the device. The
 735         resulting hash value is Base64 encoded and used to unlock the LUKS2 volume. As it should not be
 736         possible to extract the secret from the hardware token, it should not be possible to retrieve the
 737         hashed key given the configured key — without possessing the hardware token.</para>
 738
 739         <para>Note that many security tokens that implement FIDO2 also implement PKCS#11, suitable for
 740         unlocking volumes via the <option>pkcs11-uri=</option> option described above. Typically the newer,
 741         simpler FIDO2 standard is preferable.</para>
 742
 743         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 744       </varlistentry>
 745
 746       <varlistentry>
 747         <term><option>fido2-cid=</option></term>
 748
 749         <listitem><para>Takes a Base64 encoded FIDO2 client ID to use for the FIDO2 unlock operation. If
 750         specified, but <option>fido2-device=</option> is not, <option>fido2-device=auto</option> is
 751         implied. If <option>fido2-device=</option> is used but <option>fido2-cid=</option> is not, the volume
 752         must be of LUKS2 type, and the CID is read from the LUKS2 JSON token header. Use
 753         <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 754         for enrolling a FIDO2 token in the LUKS2 header compatible with this automatic
 755         mode.</para>
 756
 757         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 758       </varlistentry>
 759
 760       <varlistentry>
 761         <term><option>fido2-rp=</option></term>
 762
 763         <listitem><para>Takes a string, configuring the FIDO2 Relying Party (rp) for the FIDO2 unlock
 764         operation. If not specified <literal>io.systemd.cryptsetup</literal> is used, except if the LUKS2
 765         JSON token header contains a different value. It should normally not be necessary to override
 766         this.</para>
 767
 768         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 769       </varlistentry>
 770
 771       <varlistentry>
 772         <term><option>tpm2-device=</option></term>
 773
 774         <listitem><para>Takes either the special value <literal>auto</literal> or the path to a device node
 775         (e.g. <filename>/dev/tpmrm0</filename>) referring to a TPM2 security chip. See below for an example
 776         how to set up this mechanism for unlocking an encrypted volume with a TPM2 chip.</para>
 777
 778         <para>Use <option>tpm2-pcrs=</option> (see below) to configure the set of TPM2 PCRs to bind the
 779         volume unlocking to. Use
 780         <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 781         as simple tool for enrolling TPM2 security chips in LUKS2 volumes.</para>
 782
 783         <para>If specified as <literal>auto</literal> the TPM2 device is automatically discovered. Use
 784         <command>systemd-cryptenroll --tpm2-device=list</command> to list all suitable TPM2 devices currently
 785         available, along with their device nodes.</para>
 786
 787         <para>This option implements the following mechanism: when enrolling a TPM2 device via
 788         <command>systemd-cryptenroll</command> on a LUKS2 volume, a randomized key unlocking the volume is
 789         generated on the host and loaded into the TPM2 chip where it is encrypted with an asymmetric
 790         "primary" key pair derived from the TPM2's internal "seed" key. Neither the seed key nor the primary
 791         key are permitted to ever leave the TPM2 chip — however, the now encrypted randomized key may. It is
 792         saved in the LUKS2 volume JSON token header. When unlocking the encrypted volume, the primary key
 793         pair is generated on the TPM2 chip again (which works as long as the chip's seed key is correctly
 794         maintained by the TPM2 chip), which is then used to decrypt (on the TPM2 chip) the encrypted key from
 795         the LUKS2 volume JSON token header saved there during enrollment. The resulting decrypted key is then
 796         used to unlock the volume. When the randomized key is encrypted the current values of the selected
 797         PCRs (see below) are included in the operation, so that different PCR state results in different
 798         encrypted keys and the decrypted key can only be recovered if the same PCR state is
 799         reproduced.</para>
 800
 801         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 802       </varlistentry>
 803
 804       <varlistentry>
 805         <term><option>tpm2-pcrs=</option></term>
 806
 807         <listitem><para>Takes a <literal>+</literal> separated list of numeric TPM2 PCR (i.e. "Platform
 808         Configuration Register") indexes to bind the TPM2 volume unlocking to. This option is only useful
 809         when TPM2 enrollment metadata is not available in the LUKS2 JSON token header already, the way
 810         <command>systemd-cryptenroll</command> writes it there. If not used (and no metadata in the LUKS2
 811         JSON token header defines it), defaults to a list of a single entry: PCR 7. Assign an empty string to
 812         encode a policy that binds the key to no PCRs, making the key accessible to local programs regardless
 813         of the current PCR state.</para>
 814
 815         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 816       </varlistentry>
 817
 818       <varlistentry>
 819         <term><option>tpm2-pin=</option></term>
 820
 821         <listitem><para>Takes a boolean argument, defaults to <literal>false</literal>. Controls whether
 822         TPM2 volume unlocking is bound to a PIN in addition to PCRs. Similarly, this option is only useful
 823         when TPM2 enrollment metadata is not available.</para>
 824
 825         <xi:include href="version-info.xml" xpointer="v251"/></listitem>
 826       </varlistentry>
 827
 828       <varlistentry>
 829         <term><option>tpm2-signature=</option></term>
 830
 831         <listitem><para>Takes an absolute path to a TPM2 PCR JSON signature file, as produced by the
 832         <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 833         tool. This permits locking LUKS2 volumes to any PCR values for which a valid signature matching a
 834         public key specified at key enrollment time can be provided. See
 835         <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 836         for details on enrolling TPM2 PCR public keys. If this option is not specified but it is attempted to
 837         unlock a LUKS2 volume with a signed TPM2 PCR enrollment a suitable signature file
 838         <filename>tpm2-pcr-signature.json</filename> is searched for in <filename>/etc/systemd/</filename>,
 839         <filename>/run/systemd/</filename>, <filename>/usr/lib/systemd/</filename> (in this
 840         order).</para>
 841
 842         <xi:include href="version-info.xml" xpointer="v252"/></listitem>
 843       </varlistentry>
 844
 845       <varlistentry>
 846         <term><option>tpm2-pcrlock=</option></term>
 847
 848         <listitem><para>Takes an absolute path to a TPM2 pcrlock policy file, as produced by the
 849         <citerefentry><refentrytitle>systemd-pcrlock</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 850         tool. This permits locking LUKS2 volumes to a local policy of allowed PCR values with
 851         variants. See
 852         <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 853         for details on enrolling TPM2 pcrlock policies. If this option is not specified but it is attempted
 854         to unlock a LUKS2 volume with a TPM2 pcrlock enrollment a suitable signature file
 855         <filename>pcrlock.json</filename> is searched for in <filename>/run/systemd/</filename> and
 856         <filename>/var/lib/systemd/</filename> (in this order).</para>
 857
 858         <xi:include href="version-info.xml" xpointer="v255"/></listitem>
 859       </varlistentry>
 860
 861       <varlistentry>
 862         <term><option>tpm2-measure-pcr=</option></term>
 863
 864         <listitem><para>Controls whether to measure the volume key of the encrypted volume to a TPM2 PCR. If
 865         set to "no" (which is the default) no PCR extension is done. If set to "yes" the volume key is
 866         measured into PCR 15. If set to a decimal integer in the range 0…23 the volume key is measured into
 867         the specified PCR. The volume key is measured along with the activated volume name and its UUID. This
 868         functionality is particularly useful for the encrypted volume backing the root file system, as it
 869         then allows later TPM objects to be securely bound to the root file system and hence the specific
 870         installation.</para>
 871
 872         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 873       </varlistentry>
 874
 875       <varlistentry>
 876         <term><option>tpm2-measure-bank=</option></term>
 877
 878         <listitem><para>Selects one or more TPM2 PCR banks to measure the volume key into, as configured with
 879         <option>tpm2-measure-pcr=</option> above. Multiple banks may be specified, separated by a colon
 880         character. If not specified automatically determines available and used banks. Expects a message
 881         digest name (e.g. <literal>sha1</literal>, <literal>sha256</literal>, …) as argument, to identify the
 882         bank.</para>
 883
 884         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 885       </varlistentry>
 886
 887       <varlistentry>
 888         <term><option>token-timeout=</option></term>
 889
 890         <listitem><para>Specifies how long to wait at most for configured security devices (i.e. FIDO2,
 891         PKCS#11, TPM2) to show up. Takes a time value in seconds (but other time units may be specified too,
 892         see <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 893         for supported formats). Defaults to 30s. Once the specified timeout elapsed authentication via
 894         password is attempted. Note that this timeout applies to waiting for the security device to show up —
 895         it does not apply to the PIN prompt for the device (should one be needed) or similar. Pass 0 to turn
 896         off the time-out and wait forever.</para>
 897
 898         <xi:include href="version-info.xml" xpointer="v250"/></listitem>
 899       </varlistentry>
 900
 901       <varlistentry>
 902         <term><option>try-empty-password=</option></term>
 903
 904         <listitem><para>Takes a boolean argument. If enabled, right before asking the user for a password it
 905         is first attempted to unlock the volume with an empty password. This is useful for systems that are
 906         initialized with an encrypted volume with only an empty password set, which shall be replaced with a
 907         suitable password during first boot, but after activation.</para>
 908
 909         <xi:include href="version-info.xml" xpointer="v246"/></listitem>
 910       </varlistentry>
 911
 912       <varlistentry>
 913         <term><option>x-systemd.device-timeout=</option></term>
 914
 915         <listitem><para>Specifies how long systemd should wait for a block device to show up before
 916         giving up on the entry. The argument is a time in seconds or explicitly specified units of
 917         <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>ms</literal>.
 918         </para>
 919
 920         <xi:include href="version-info.xml" xpointer="v216"/></listitem>
 921       </varlistentry>
 922
 923       <varlistentry>
 924         <term><option>x-initrd.attach</option></term>
 925
 926         <listitem><para>Setup this encrypted block device in the initrd, similarly to
 927         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 928         units marked with <option>x-initrd.mount</option>.</para>
 929
 930         <para>Although it's not necessary to mark the mount entry for the root file system with
 931         <option>x-initrd.mount</option>, <option>x-initrd.attach</option> is still recommended with
 932         the encrypted block device containing the root file system as otherwise systemd will
 933         attempt to detach the device during the regular system shutdown while it's still in
 934         use. With this option the device will still be detached but later after the root file
 935         system is unmounted.</para>
 936
 937         <para>All other encrypted block devices that contain file systems mounted in the initrd should use
 938         this option.</para>
 939
 940         <xi:include href="version-info.xml" xpointer="v245"/>
 941         </listitem>
 942       </varlistentry>
 943
 944     </variablelist>
 945
 946     <para>At early boot and when the system manager configuration is
 947     reloaded, this file is translated into native systemd units by
 948     <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 949   </refsect1>
 950
 951   <refsect1>
 952     <title><constant>AF_UNIX</constant> Key Files</title>
 953
 954     <para>If the key file path (as specified in the third column of <filename>/etc/crypttab</filename>
 955     entries, see above) refers to an <constant>AF_UNIX</constant> stream socket in the file system, the key
 956     is acquired by connecting to the socket and reading the key from the connection. The connection is made
 957     from an <constant>AF_UNIX</constant> socket name in the abstract namespace, see <citerefentry
 958     project='man-pages'><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 959     details. The source socket name is chosen according to the following format:</para>
 960
 961     <programlisting><constant>NUL</constant> <replaceable>RANDOM</replaceable> /cryptsetup/ <replaceable>VOLUME</replaceable></programlisting>
 962
 963     <para>In other words: a <constant>NUL</constant> byte (as required for abstract namespace sockets),
 964     followed by a random string (consisting of alphanumeric characters only), followed by the literal
 965     string <literal>/cryptsetup/</literal>, followed by the name of the volume to acquire they key
 966     for. For example, for the volume <literal>myvol</literal>:</para>
 967
 968     <programlisting>\0d7067f78d9827418/cryptsetup/myvol</programlisting>
 969
 970     <para>Services listening on the <constant>AF_UNIX</constant> stream socket may query the source socket
 971     name with <citerefentry
 972     project='man-pages'><refentrytitle>getpeername</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 973     and use this to determine which key to send, allowing a single listening socket to serve keys for
 974     multiple volumes. If the PKCS#11 logic is used (see above), the socket source name is picked in similar
 975     fashion, except that the literal string <literal>/cryptsetup-pkcs11/</literal> is used. And similarly for
 976     FIDO2 (<literal>/cryptsetup-fido2/</literal>) and TPM2 (<literal>/cryptsetup-tpm2/</literal>). A different
 977     path component is used so that services providing key material know that the secret key was not requested
 978     directly, but instead an encrypted key that will be decrypted via the PKCS#11/FIDO2/TPM2 logic to acquire
 979     the final secret key.</para>
 980   </refsect1>
 981
 982   <refsect1>
 983     <title>Examples</title>
 984     <example>
 985       <title>/etc/crypttab example</title>
 986       <para>Set up four encrypted block devices. One using LUKS for normal storage, another one for usage as
 987       a swap device and two TrueCrypt volumes. For the fourth device, the option string is interpreted as two
 988       options <literal>cipher=xchacha12,aes-adiantum-plain64</literal>,
 989       <literal>keyfile-timeout=10s</literal>.</para>
 990
 991       <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
 992 swap       /dev/sda7       /dev/urandom       swap
 993 truecrypt  /dev/sda2       /etc/container_password  tcrypt
 994 hidden     /mnt/tc_hidden  /dev/null    tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
 995 external   /dev/sda3       keyfile:LABEL=keydev keyfile-timeout=10s,cipher=xchacha12\,aes-adiantum-plain64
 996 </programlisting>
 997     </example>
 998
 999     <example>
1000       <title>Yubikey-based PKCS#11 Volume Unlocking Example</title>
1001
1002       <para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA
1003       or EC cryptographic keys for unlocking an encrypted volume. Here's an example how to set up a Yubikey
1004       security token for this purpose on a LUKS2 volume, using <citerefentry
1005       project='debian'><refentrytitle>ykmap</refentrytitle><manvolnum>1</manvolnum></citerefentry> from the
1006       yubikey-manager project to initialize the token and
1007       <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1008       to add it in the LUKS2 volume:</para>
1009
1010       <programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting>
1011
1012       <para>A few notes on the above:</para>
1013
1014       <itemizedlist>
1015         <listitem><para>We use RSA2048, which is the longest key size current Yubikeys support</para></listitem>
1016         <listitem><para>We use Yubikey key slot 9d, since that's apparently the keyslot to use for decryption purposes,
1017         see
1018         <ulink url="https://developers.yubico.com/PIV/Introduction/Certificate_slots.html">Yubico PIV certificate slots</ulink>.
1019         </para></listitem>
1020       </itemizedlist>
1021     </example>
1022
1023     <example>
1024       <title>FIDO2 Volume Unlocking Example</title>
1025
1026       <para>The FIDO2 logic allows using any compatible FIDO2 security token that implements the
1027       <literal>hmac-secret</literal> extension for unlocking an encrypted volume. Here's an example how to
1028       set up a FIDO2 security token for this purpose for a LUKS2 volume, using
1029       <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>:</para>
1030
1031       <programlisting><xi:include href="fido2-crypttab.sh" parse="text" /></programlisting>
1032     </example>
1033
1034     <example>
1035       <title>TPM2 Volume Unlocking Example</title>
1036
1037       <para>The TPM2 logic allows using any TPM2 chip supported by the Linux kernel for unlocking an
1038       encrypted volume. Here's an example how to set up a TPM2 chip for this purpose for a LUKS2 volume,
1039       using
1040       <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>:</para>
1041
1042       <programlisting><xi:include href="tpm2-crypttab.sh" parse="text" /></programlisting>
1043     </example>
1044   </refsect1>
1045
1046   <refsect1>
1047     <title>See Also</title>
1048     <para><simplelist type="inline">
1049       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
1050       <member><citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1051       <member><citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1052       <member><citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
1053       <member><citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
1054       <member><citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1055       <member><citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1056       <member><citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
1057     </simplelist></para>
1058   </refsect1>
1059
1060 </refentry>