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/4.2/docbookx.dtd">
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   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
  49     three encryption modes: LUKS, TrueCrypt and plain. See
  50     <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  51     for more information about each mode. When no mode is specified in
  52     the options field and the block device contains a LUKS signature,
  53     it is opened as a LUKS device; otherwise, it is assumed to be in
  54     raw dm-crypt (plain mode) format.</para>
  55
  56     <para>The first field contains the name of the resulting encrypted volume; its block device is set up
  57     below <filename>/dev/mapper/</filename>.</para>
  58
  59     <para>The second field contains a path to the underlying block
  60     device or file, or a specification of a block device via
  61     <literal>UUID=</literal> followed by the UUID.</para>
  62
  63     <para>The third field specifies an absolute path to a file to read the encryption key from. If the field
  64     is not present or set to <literal>none</literal> or <literal>-</literal>, a key file named after the
  65     volume to unlock (i.e. the first column of the line), suffixed with <filename>.key</filename> is
  66     automatically loaded from the <filename>/etc/cryptsetup-keys.d/</filename> and
  67     <filename>/run/cryptsetup-keys.d/</filename> directories, if present. Otherwise, the password has to be
  68     manually entered during system boot. For swap encryption, <filename>/dev/urandom</filename> may be used
  69     as key file.</para>
  70
  71     <para>The fourth field, if present, is a comma-delimited list of
  72     options. The following options are recognized:</para>
  73
  74     <variablelist class='fstab-options'>
  75
  76       <varlistentry>
  77         <term><option>cipher=</option></term>
  78
  79         <listitem><para>Specifies the cipher to use. See
  80         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  81         for possible values and the default value of this option. A
  82         cipher with unpredictable IV values, such as
  83         <literal>aes-cbc-essiv:sha256</literal>, is
  84         recommended.</para></listitem>
  85       </varlistentry>
  86
  87       <varlistentry>
  88         <term><option>discard</option></term>
  89
  90         <listitem><para>Allow discard requests to be passed through the encrypted block
  91         device. This improves performance on SSD storage but has security implications.
  92         </para></listitem>
  93       </varlistentry>
  94
  95       <varlistentry>
  96         <term><option>hash=</option></term>
  97
  98         <listitem><para>Specifies the hash to use for password
  99         hashing. See
 100         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 101         for possible values and the default value of this
 102         option.</para></listitem>
 103       </varlistentry>
 104
 105       <varlistentry>
 106         <term><option>header=</option></term>
 107
 108         <listitem><para>Use a detached (separated) metadata device or
 109         file where the LUKS header is stored. This option is only
 110         relevant for LUKS devices. See
 111         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 112         for possible values and the default value of this
 113         option.</para></listitem>
 114       </varlistentry>
 115
 116       <varlistentry>
 117         <term><option>keyfile-offset=</option></term>
 118
 119         <listitem><para>Specifies the number of bytes to skip at the
 120         start of the key file. See
 121         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 122         for possible values and the default value of this
 123         option.</para></listitem>
 124       </varlistentry>
 125
 126       <varlistentry>
 127         <term><option>keyfile-size=</option></term>
 128
 129         <listitem><para>Specifies the maximum number of bytes to read
 130         from the key file. See
 131         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 132         for possible values and the default value of this option. This
 133         option is ignored in plain encryption mode, as the key file
 134         size is then given by the key size.</para></listitem>
 135       </varlistentry>
 136
 137       <varlistentry>
 138         <term><option>keyfile-erase</option></term>
 139
 140         <listitem><para>If enabled, the specified key file is erased after the volume is activated or when
 141         activation fails. This is in particular useful when the key file is only acquired transiently before
 142         activation (e.g. via a file in <filename>/run/</filename>, generated by a service running before
 143         activation), and shall be removed after use. Defaults to off.</para></listitem>
 144       </varlistentry>
 145
 146       <varlistentry>
 147         <term><option>key-slot=</option></term>
 148
 149         <listitem><para>Specifies the key slot to compare the
 150         passphrase or key against. If the key slot does not match the
 151         given passphrase or key, but another would, the setup of the
 152         device will fail regardless. This option implies
 153         <option>luks</option>. See
 154         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 155         for possible values. The default is to try all key slots in
 156         sequential order.</para></listitem>
 157       </varlistentry>
 158
 159       <varlistentry>
 160         <term><option>keyfile-timeout=</option></term>
 161
 162         <listitem><para> Specifies the timeout for the device on
 163         which the key file resides and falls back to a password if
 164         it could not be mounted. See
 165         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 166         for key files on external devices.
 167         </para></listitem>
 168       </varlistentry>
 169
 170       <varlistentry>
 171         <term><option>luks</option></term>
 172
 173         <listitem><para>Force LUKS mode. When this mode is used, the
 174         following options are ignored since they are provided by the
 175         LUKS header on the device: <option>cipher=</option>,
 176         <option>hash=</option>,
 177         <option>size=</option>.</para></listitem>
 178       </varlistentry>
 179
 180       <varlistentry>
 181         <term><option>bitlk</option></term>
 182
 183         <listitem><para>Decrypt Bitlocker drive. Encryption parameters
 184         are deduced by cryptsetup from Bitlocker header.</para></listitem>
 185       </varlistentry>
 186
 187       <varlistentry>
 188         <term><option>_netdev</option></term>
 189
 190         <listitem><para>Marks this cryptsetup device as requiring network. It will be
 191         started after the network is available, similarly to
 192         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 193         units marked with <option>_netdev</option>. The service unit to set up this device
 194         will be ordered between <filename>remote-fs-pre.target</filename> and
 195         <filename>remote-cryptsetup.target</filename>, instead of
 196         <filename>cryptsetup-pre.target</filename> and
 197         <filename>cryptsetup.target</filename>.</para>
 198
 199         <para>Hint: if this device is used for a mount point that is specified in
 200         <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 201         the <option>_netdev</option> option should also be used for the mount
 202         point. Otherwise, a dependency loop might be created where the mount point
 203         will be pulled in by <filename>local-fs.target</filename>, while the
 204         service to configure the network is usually only started <emphasis>after</emphasis>
 205         the local file system has been mounted.</para>
 206         </listitem>
 207       </varlistentry>
 208
 209       <varlistentry>
 210         <term><option>noauto</option></term>
 211
 212         <listitem><para>This device will not be added to <filename>cryptsetup.target</filename>.
 213         This means that it will not be automatically unlocked on boot, unless something else pulls
 214         it in. In particular, if the device is used for a mount point, it'll be unlocked
 215         automatically during boot, unless the mount point itself is also disabled with
 216         <option>noauto</option>.</para></listitem>
 217       </varlistentry>
 218
 219       <varlistentry>
 220         <term><option>nofail</option></term>
 221
 222         <listitem><para>This device will not be a hard dependency of
 223         <filename>cryptsetup.target</filename>. It'll still be pulled in and started, but the system
 224         will not wait for the device to show up and be unlocked, and boot will not fail if this is
 225         unsuccessful. Note that other units that depend on the unlocked device may still fail. In
 226         particular, if the device is used for a mount point, the mount point itself also needs to
 227         have the <option>nofail</option> option, or the boot will fail if the device is not unlocked
 228         successfully.</para></listitem>
 229       </varlistentry>
 230
 231       <varlistentry>
 232         <term><option>offset=</option></term>
 233
 234         <listitem><para>Start offset in the backend device, in 512-byte sectors. This
 235         option is only relevant for plain devices.</para></listitem>
 236       </varlistentry>
 237
 238       <varlistentry>
 239         <term><option>plain</option></term>
 240
 241         <listitem><para>Force plain encryption mode.</para></listitem>
 242       </varlistentry>
 243
 244       <varlistentry>
 245         <term><option>read-only</option></term><term><option>readonly</option></term>
 246
 247         <listitem><para>Set up the encrypted block device in read-only
 248         mode.</para></listitem>
 249       </varlistentry>
 250
 251       <varlistentry>
 252         <term><option>same-cpu-crypt</option></term>
 253
 254         <listitem><para>Perform encryption using the same cpu that IO was submitted on. The default is to use
 255         an unbound workqueue so that encryption work is automatically balanced between available CPUs.</para>
 256         <para>This requires kernel 4.0 or newer.</para>
 257         </listitem>
 258       </varlistentry>
 259
 260       <varlistentry>
 261         <term><option>submit-from-crypt-cpus</option></term>
 262
 263         <listitem><para>Disable offloading writes to a separate thread after encryption. There are some
 264         situations where offloading write bios from the encryption threads to a single thread degrades
 265         performance significantly. The default is to offload write bios to the same thread because it benefits
 266         CFQ to have writes submitted using the same context.</para>
 267         <para>This requires kernel 4.0 or newer.</para>
 268         </listitem>
 269       </varlistentry>
 270
 271       <varlistentry>
 272         <term><option>skip=</option></term>
 273
 274         <listitem><para>How many 512-byte sectors of the encrypted data to skip at the
 275         beginning. This is different from the <option>offset=</option> option with respect
 276         to the sector numbers used in initialization vector (IV) calculation. Using
 277         <option>offset=</option> will shift the IV calculation by the same negative
 278         amount. Hence, if <option>offset=<replaceable>n</replaceable></option> is given,
 279         sector <replaceable>n</replaceable> will get a sector number of 0 for the IV
 280         calculation. Using <option>skip=</option> causes sector
 281         <replaceable>n</replaceable> to also be the first sector of the mapped device, but
 282         with its number for IV generation being <replaceable>n</replaceable>.</para>
 283
 284         <para>This option is only relevant for plain devices.</para>
 285         </listitem>
 286       </varlistentry>
 287
 288       <varlistentry>
 289         <term><option>size=</option></term>
 290
 291         <listitem><para>Specifies the key size in bits. See
 292         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 293         for possible values and the default value of this
 294         option.</para></listitem>
 295       </varlistentry>
 296
 297       <varlistentry>
 298         <term><option>sector-size=</option></term>
 299
 300         <listitem><para>Specifies the sector size in bytes. See
 301         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 302         for possible values and the default value of this
 303         option.</para></listitem>
 304       </varlistentry>
 305
 306       <varlistentry>
 307         <term><option>swap</option></term>
 308
 309         <listitem><para>The encrypted block device will be used as a
 310         swap device, and will be formatted accordingly after setting
 311         up the encrypted block device, with
 312         <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 313         This option implies <option>plain</option>.</para>
 314
 315         <para>WARNING: Using the <option>swap</option> option will
 316         destroy the contents of the named partition during every boot,
 317         so make sure the underlying block device is specified
 318         correctly.</para></listitem>
 319       </varlistentry>
 320
 321       <varlistentry>
 322         <term><option>tcrypt</option></term>
 323
 324         <listitem><para>Use TrueCrypt encryption mode. When this mode
 325         is used, the following options are ignored since they are
 326         provided by the TrueCrypt header on the device or do not
 327         apply:
 328         <option>cipher=</option>,
 329         <option>hash=</option>,
 330         <option>keyfile-offset=</option>,
 331         <option>keyfile-size=</option>,
 332         <option>size=</option>.</para>
 333
 334         <para>When this mode is used, the passphrase is read from the
 335         key file given in the third field. Only the first line of this
 336         file is read, excluding the new line character.</para>
 337
 338         <para>Note that the TrueCrypt format uses both passphrase and
 339         key files to derive a password for the volume. Therefore, the
 340         passphrase and all key files need to be provided. Use
 341         <option>tcrypt-keyfile=</option> to provide the absolute path
 342         to all key files. When using an empty passphrase in
 343         combination with one or more key files, use
 344         <literal>/dev/null</literal> as the password file in the third
 345         field.</para></listitem>
 346       </varlistentry>
 347
 348       <varlistentry>
 349         <term><option>tcrypt-hidden</option></term>
 350
 351         <listitem><para>Use the hidden TrueCrypt volume. This option
 352         implies <option>tcrypt</option>.</para>
 353
 354         <para>This will map the hidden volume that is inside of the
 355         volume provided in the second field. Please note that there is
 356         no protection for the hidden volume if the outer volume is
 357         mounted instead. See
 358         <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 359         for more information on this limitation.</para></listitem>
 360       </varlistentry>
 361
 362       <varlistentry>
 363         <term><option>tcrypt-keyfile=</option></term>
 364
 365         <listitem><para>Specifies the absolute path to a key file to
 366         use for a TrueCrypt volume. This implies
 367         <option>tcrypt</option> and can be used more than once to
 368         provide several key files.</para>
 369
 370         <para>See the entry for <option>tcrypt</option> on the
 371         behavior of the passphrase and key files when using TrueCrypt
 372         encryption mode.</para></listitem>
 373       </varlistentry>
 374
 375       <varlistentry>
 376         <term><option>tcrypt-system</option></term>
 377
 378         <listitem><para>Use TrueCrypt in system encryption mode. This
 379         option implies <option>tcrypt</option>.</para></listitem>
 380       </varlistentry>
 381
 382       <varlistentry>
 383         <term><option>tcrypt-veracrypt</option></term>
 384
 385         <listitem><para>Check for a VeraCrypt volume.  VeraCrypt is a fork of
 386         TrueCrypt that is mostly compatible, but uses different, stronger key
 387         derivation algorithms that cannot be detected without this flag.
 388         Enabling this option could substantially slow down unlocking, because
 389         VeraCrypt's key derivation takes much longer than TrueCrypt's.  This
 390         option implies <option>tcrypt</option>.</para></listitem>
 391       </varlistentry>
 392
 393       <varlistentry>
 394         <term><option>timeout=</option></term>
 395
 396         <listitem><para>Specifies the timeout for querying for a
 397         password. If no unit is specified, seconds is used. Supported
 398         units are s, ms, us, min, h, d. A timeout of 0 waits
 399         indefinitely (which is the default).</para></listitem>
 400       </varlistentry>
 401
 402       <varlistentry>
 403         <term><option>tmp=</option></term>
 404
 405         <listitem><para>The encrypted block device will be prepared for using it as
 406         <filename>/tmp/</filename>; it will be formatted using <citerefentry
 407         project='man-pages'><refentrytitle>mkfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes
 408         a file system type as argument, such as <literal>ext4</literal>, <literal>xfs</literal> or
 409         <literal>btrfs</literal>. If no argument is specified defaults to <literal>ext4</literal>. This
 410         option implies <option>plain</option>.</para>
 411
 412         <para>WARNING: Using the <option>tmp</option> option will destroy the contents of the named partition
 413         during every boot, so make sure the underlying block device is specified correctly.</para></listitem>
 414       </varlistentry>
 415
 416       <varlistentry>
 417         <term><option>tries=</option></term>
 418
 419         <listitem><para>Specifies the maximum number of times the user
 420         is queried for a password. The default is 3. If set to 0, the
 421         user is queried for a password indefinitely.</para></listitem>
 422       </varlistentry>
 423
 424       <varlistentry>
 425         <term><option>verify</option></term>
 426
 427         <listitem><para>If the encryption password is read from console, it has to be entered twice to
 428         prevent typos.</para></listitem>
 429       </varlistentry>
 430
 431       <varlistentry>
 432         <term><option>pkcs11-uri=</option></term>
 433
 434         <listitem><para>Takes a <ulink url="https://tools.ietf.org/html/rfc7512">RFC7512 PKCS#11 URI</ulink>
 435         pointing to a private RSA key which is used to decrypt the key specified in the third column of the
 436         line. This is useful for unlocking encrypted volumes through security tokens or smartcards. See below
 437         for an example how to set up this mechanism for unlocking a LUKS volume with a YubiKey security
 438         token. The specified URI can refer directly to a private RSA key stored on a token or alternatively
 439         just to a slot or token, in which case a search for a suitable private RSA key will be performed.  In
 440         this case if multiple suitable objects are found the token is refused. The key configured in the
 441         third column is passed as is to RSA decryption. The resulting decrypted key is then base64 encoded
 442         before it is used to unlock the LUKS volume.</para></listitem>
 443       </varlistentry>
 444
 445       <varlistentry>
 446         <term><option>try-empty-password=</option></term>
 447
 448         <listitem><para>Takes a boolean argument. If enabled, right before asking the user for a password it
 449         is first attempted to unlock the volume with an empty password. This is useful for systems that are
 450         initialized with an encrypted volume with only an empty password set, which shall be replaced with a
 451         suitable password during first boot, but after activation.</para></listitem>
 452       </varlistentry>
 453
 454       <varlistentry>
 455         <term><option>x-systemd.device-timeout=</option></term>
 456
 457         <listitem><para>Specifies how long systemd should wait for a device to show up
 458         before giving up on the entry. The argument is a time in seconds or explicitly
 459         specified units of
 460         <literal>s</literal>,
 461         <literal>min</literal>,
 462         <literal>h</literal>,
 463         <literal>ms</literal>.
 464         </para></listitem>
 465       </varlistentry>
 466
 467       <varlistentry>
 468         <term><option>x-initrd.attach</option></term>
 469
 470         <listitem><para>Setup this encrypted block device in the initramfs, similarly to
 471         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 472         units marked with <option>x-initrd.mount</option>.</para>
 473
 474         <para>Although it's not necessary to mark the mount entry for the root file system with
 475         <option>x-initrd.mount</option>, <option>x-initrd.attach</option> is still recommended with
 476         the encrypted block device containing the root file system as otherwise systemd will
 477         attempt to detach the device during the regular system shutdown while it's still in
 478         use. With this option the device will still be detached but later after the root file
 479         system is unmounted.</para>
 480
 481         <para>All other encrypted block devices that contain file systems mounted in the initramfs
 482         should use this option.</para>
 483         </listitem>
 484       </varlistentry>
 485
 486     </variablelist>
 487
 488     <para>At early boot and when the system manager configuration is
 489     reloaded, this file is translated into native systemd units by
 490     <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 491   </refsect1>
 492
 493   <refsect1>
 494     <title>Examples</title>
 495     <example>
 496       <title>/etc/crypttab example</title>
 497       <para>Set up four encrypted block devices. One using LUKS for
 498       normal storage, another one for usage as a swap device and two
 499       TrueCrypt volumes.</para>
 500
 501       <programlisting>luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
 502 swap       /dev/sda7       /dev/urandom       swap
 503 truecrypt  /dev/sda2       /etc/container_password  tcrypt
 504 hidden     /mnt/tc_hidden  /dev/null    tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
 505 external   /dev/sda3       keyfile:LABEL=keydev keyfile-timeout=10s</programlisting>
 506     </example>
 507
 508     <example>
 509       <title>Yubikey-based Volume Unlocking Example</title>
 510
 511       <para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA
 512       decryption keys. Here's an example how to set up a Yubikey security token for this purpose, using
 513       <command>ykman</command> from the yubikey-manager project:</para>
 514
 515 <programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting>
 516
 517 <para>A few notes on the above:</para>
 518
 519 <itemizedlist>
 520   <listitem><para>We use RSA (and not ECC), since Yubikeys support PKCS#11 Decrypt() only for RSA keys</para></listitem>
 521   <listitem><para>We use RSA2048, which is the longest key size current Yubikeys support</para></listitem>
 522   <listitem><para>LUKS key size must be shorter than 2048bit due to RSA padding, hence we use 128 bytes</para></listitem>
 523   <listitem><para>We use Yubikey key slot 9d, since that's apparently the keyslot to use for decryption purposes,
 524   <ulink url="https://developers.yubico.com/PIV/Introduction/Certificate_slots.html">see
 525   documentation</ulink>.</para></listitem>
 526 </itemizedlist>
 527
 528     </example>
 529   </refsect1>
 530
 531   <refsect1>
 532     <title>See Also</title>
 533     <para>
 534       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 535       <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 536       <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 537       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 538       <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 539       <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 540       <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 541     </para>
 542   </refsect1>
 543
 544 </refentry>