man/veritytab.xml

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   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1-or-later
   7
   8 This is based on crypttab(5).
   9
  10 -->
  11 <refentry id="veritytab" conditional='HAVE_LIBCRYPTSETUP' xmlns:xi="http://www.w3.org/2001/XInclude">
  12
  13   <refentryinfo>
  14     <title>veritytab</title>
  15     <productname>systemd</productname>
  16   </refentryinfo>
  17
  18   <refmeta>
  19     <refentrytitle>veritytab</refentrytitle>
  20     <manvolnum>5</manvolnum>
  21   </refmeta>
  22
  23   <refnamediv>
  24     <refname>veritytab</refname>
  25     <refpurpose>Configuration for verity block devices</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <para><filename>/etc/veritytab</filename></para>
  30   </refsynopsisdiv>
  31
  32   <refsect1>
  33     <title>Description</title>
  34
  35     <para>The <filename>/etc/veritytab</filename> file describes
  36     verity protected block devices that are set up during
  37     system boot.</para>
  38
  39     <para>Empty lines and lines starting with the <literal>#</literal>
  40     character are ignored. Each of the remaining lines describes one
  41     verity protected block device. Fields are delimited by
  42     white space.</para>
  43
  44     <para>Each line is in the form<programlisting><replaceable>volume-name</replaceable> <replaceable>data-device</replaceable> <replaceable>hash-device</replaceable> <replaceable>roothash</replaceable> <optional><replaceable>options</replaceable></optional></programlisting>
  45     The first four fields are mandatory, the remaining one is optional.</para>
  46
  47     <para>The first field contains the name of the resulting verity volume; its block device is set up
  48     below <filename>/dev/mapper/</filename>.</para>
  49
  50     <para>The second field contains a path to the underlying block data device, or a specification of a block device via
  51     <varname>UUID=</varname> followed by the <replaceable>UUID</replaceable>.</para>
  52
  53     <para>The third field contains a path to the underlying block hash device, or a specification of a block device via
  54     <varname>UUID=</varname> followed by the <replaceable>UUID</replaceable>.</para>
  55
  56     <para>The fourth field is the <replaceable>roothash</replaceable> in hexadecimal.</para>
  57
  58     <para>The fifth field, if present, is a comma-delimited list of options. The following options are
  59     recognized:</para>
  60
  61     <variablelist class='fstab-options'>
  62
  63       <varlistentry>
  64         <term><option>superblock=<replaceable>BOOL</replaceable></option></term>
  65
  66         <listitem><para>Use dm-verity with or without permanent on-disk superblock.</para>
  67
  68         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
  69       </varlistentry>
  70
  71       <varlistentry>
  72         <term><option>format=<replaceable>NUMBER</replaceable></option></term>
  73
  74         <listitem><para>Specifies the hash version type. Format type <literal>0</literal> is original Chrome OS version. Format type <literal>1</literal> is
  75         modern version.</para>
  76
  77         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
  78       </varlistentry>
  79
  80       <varlistentry>
  81         <term><option>data-block-size=<replaceable>BYTES</replaceable></option></term>
  82
  83         <listitem><para>Used block size for the data device. (Note kernel supports only page-size as maximum
  84         here; Multiples of 512 bytes.) </para>
  85
  86         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
  87       </varlistentry>
  88
  89       <varlistentry>
  90         <term><option>hash-block-size=<replaceable>BYTES</replaceable></option></term>
  91
  92         <listitem><para>Used block size for the hash device. (Note kernel supports only page-size as maximum
  93         here; Multiples of 512 bytes.)</para>
  94
  95         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
  96       </varlistentry>
  97
  98       <varlistentry>
  99         <term><option>data-blocks=<replaceable>BLOCKS</replaceable></option></term>
 100
 101         <listitem><para>Number of blocks of data device used in verification. If not specified, the whole device is
 102         used.</para>
 103
 104         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 105       </varlistentry>
 106
 107       <varlistentry>
 108         <term><option>hash-offset=<replaceable>BYTES</replaceable></option></term>
 109
 110         <listitem><para>Offset of hash area/superblock on <literal>hash-device</literal>. (Multiples of 512 bytes.)
 111         </para>
 112
 113         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 114       </varlistentry>
 115
 116       <varlistentry>
 117         <term><option>salt=<replaceable>HEX</replaceable></option></term>
 118
 119         <listitem><para>Salt used for format or verification. Format is a hexadecimal string; 256 bytes long maximum;
 120         <literal>-</literal> is the special value for empty.</para>
 121
 122         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 123       </varlistentry>
 124
 125       <varlistentry>
 126         <term><option>uuid=<replaceable>UUID</replaceable></option></term>
 127
 128         <listitem><para>Use the provided <replaceable>UUID</replaceable> instead of generating new one. The <replaceable>UUID</replaceable> must be
 129         provided in standard <acronym>UUID</acronym> format, e.g. <literal>12345678-1234-1234-1234-123456789abc</literal>.</para>
 130
 131         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 132       </varlistentry>
 133
 134       <varlistentry>
 135         <term><option>ignore-corruption</option></term>
 136         <term><option>restart-on-corruption</option></term>
 137         <term><option>panic-on-corruption</option></term>
 138
 139         <listitem><para>Defines what to do if a data verity problem is detected (data corruption). Without these
 140         options kernel fails the <acronym>IO</acronym> operation with <acronym>I/O</acronym> error. With <option>--ignore-corruption</option> option the
 141         corruption is only logged. With <option>--restart-on-corruption</option> or
 142         <option>--panic-on-corruption</option> the kernel is restarted (panicked) immediately.
 143
 144         (You have to provide way how to avoid restart loops.)</para>
 145
 146         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 147       </varlistentry>
 148
 149       <varlistentry>
 150         <term><option>ignore-zero-blocks</option></term>
 151
 152         <listitem><para>Instruct kernel to not verify blocks that are expected to contain zeroes and always directly
 153         return zeroes instead.</para>
 154
 155         <warning>
 156           <para>Use this option only in very specific cases. This option is available since Linux kernel version 4.5.</para>
 157         </warning>
 158
 159         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 160       </varlistentry>
 161
 162       <varlistentry>
 163         <term><option>check-at-most-once</option></term>
 164
 165         <listitem><para>Instruct kernel to verify blocks only the first time they are read from the data device, rather
 166         than every time.</para>
 167
 168         <warning>
 169           <para>It provides a reduced level of security because only offline tampering of the data device's content
 170           will be detected, not online tampering. This option is available since Linux kernel version 4.17.</para>
 171         </warning>
 172
 173         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 174       </varlistentry>
 175
 176       <varlistentry>
 177         <term><option>hash=<replaceable>HASH</replaceable></option></term>
 178
 179         <listitem><para>Hash algorithm for dm-verity. This should be the name of the algorithm, like "sha1". For default
 180         see <command>veritysetup --help</command>.</para>
 181
 182         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 183       </varlistentry>
 184
 185       <varlistentry>
 186         <term><option>fec-device=<replaceable>PATH</replaceable></option></term>
 187
 188         <listitem><para>Use forward error correction (<acronym>FEC</acronym>) to recover from corruption if hash verification fails. Use
 189         encoding data from the specified device. The fec device argument can be block device or file image.
 190         If fec device path doesn't exist, it will be created as file. Note: block sizes for data and hash devices must
 191         match. Also, if the verity data_device is encrypted the fec_device should be too.</para>
 192
 193         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 194       </varlistentry>
 195
 196       <varlistentry>
 197         <term><option>fec-offset=<replaceable>BYTES</replaceable></option></term>
 198
 199         <listitem><para>This is the offset, in bytes, from the start of the <acronym>FEC</acronym> device to the beginning of the encoding
 200         data. (Aligned on 512 bytes.)</para>
 201
 202         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 203       </varlistentry>
 204
 205       <varlistentry>
 206         <term><option>fec-roots=<replaceable>NUM</replaceable></option></term>
 207
 208         <listitem><para>Number of generator roots. This equals to the number of parity bytes in the encoding data. In
 209         RS(M, N) encoding, the number of roots is M-N. M is 255 and M-N is between 2 and 24 (including).</para>
 210
 211         <xi:include href="version-info.xml" xpointer="v254"/>
 212         </listitem>
 213       </varlistentry>
 214
 215       <varlistentry>
 216         <term><option>root-hash-signature=<replaceable>PATH</replaceable>|base64:<replaceable>HEX</replaceable></option></term>
 217
 218         <listitem><para>A base64 string encoding the root hash signature prefixed by <literal>base64:</literal> or a
 219         path to roothash signature file used to verify the root hash (in kernel). This feature requires Linux kernel
 220         version 5.4 or more recent.</para>
 221
 222         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 223       </varlistentry>
 224
 225       <varlistentry>
 226         <term><option>_netdev</option></term>
 227
 228         <listitem><para>Marks this veritysetup device as requiring network. It will be
 229         started after the network is available, similarly to
 230         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 231         units marked with <option>_netdev</option>. The service unit to set up this device
 232         will be ordered between <filename>remote-fs-pre.target</filename> and
 233         <filename>remote-veritysetup.target</filename>, instead of
 234         <filename>veritysetup-pre.target</filename> and
 235         <filename>veritysetup.target</filename>.</para>
 236
 237         <para>Hint: if this device is used for a mount point that is specified in
 238         <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 239         the <option>_netdev</option> option should also be used for the mount
 240         point. Otherwise, a dependency loop might be created where the mount point
 241         will be pulled in by <filename>local-fs.target</filename>, while the
 242         service to configure the network is usually only started <emphasis>after</emphasis>
 243         the local file system has been mounted.</para>
 244
 245         <xi:include href="version-info.xml" xpointer="v248"/>
 246         </listitem>
 247       </varlistentry>
 248
 249       <varlistentry>
 250         <term><option>noauto</option></term>
 251
 252         <listitem><para>This device will not be added to <filename>veritysetup.target</filename>.
 253         This means that it will not be automatically enabled on boot, unless something else pulls
 254         it in. In particular, if the device is used for a mount point, it'll be enabled
 255         automatically during boot, unless the mount point itself is also disabled with
 256         <option>noauto</option>.</para>
 257
 258         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 259       </varlistentry>
 260
 261       <varlistentry>
 262         <term><option>nofail</option></term>
 263
 264         <listitem><para>This device will not be a hard dependency of
 265         <filename>veritysetup.target</filename>. It'll still be pulled in and started, but the system
 266         will not wait for the device to show up and be enabled, and boot will not fail if this is
 267         unsuccessful. Note that other units that depend on the enabled device may still fail. In
 268         particular, if the device is used for a mount point, the mount point itself also needs to
 269         have the <option>nofail</option> option, or the boot will fail if the device is not enabled
 270         successfully.</para>
 271
 272         <xi:include href="version-info.xml" xpointer="v248"/></listitem>
 273       </varlistentry>
 274
 275       <varlistentry>
 276         <term><option>x-initrd.attach</option></term>
 277
 278         <listitem><para>Setup this verity protected block device in the initrd, similarly to
 279         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 280         units marked with <option>x-initrd.mount</option>.</para>
 281
 282         <para>Although it's not necessary to mark the mount entry for the root file system with
 283         <option>x-initrd.mount</option>, <option>x-initrd.attach</option> is still recommended with
 284         the verity protected block device containing the root file system as otherwise systemd
 285         will attempt to detach the device during the regular system shutdown while it's still in
 286         use. With this option the device will still be detached but later after the root file
 287         system is unmounted.</para>
 288
 289         <para>All other verity protected block devices that contain file systems mounted in the initrd should
 290         use this option.</para>
 291
 292         <xi:include href="version-info.xml" xpointer="v248"/>
 293         </listitem>
 294       </varlistentry>
 295
 296     </variablelist>
 297
 298     <para>At early boot and when the system manager configuration is
 299     reloaded, this file is translated into native systemd units by
 300     <citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 301   </refsect1>
 302
 303   <refsect1>
 304     <title>Examples</title>
 305     <example>
 306       <title>/etc/veritytab example</title>
 307       <para>Set up two verity protected block devices. One using device blocks, another using files.</para>
 308
 309       <programlisting>usr  PARTUUID=783e45ae-7aa3-484a-beef-a80ff9c19cbb PARTUUID=21dc1dfe-4c33-8b48-98a9-918a22eb3e37 36e3f740ad502e2c25e2a23d9c7c17bf0fdad2300b7580842d4b7ec1fb0fa263 auto
 310 data /etc/data /etc/hash a5ee4b42f70ae1f46a08a7c92c2e0a20672ad2f514792730f5d49d7606ab8fdf auto
 311 </programlisting>
 312     </example>
 313   </refsect1>
 314
 315   <refsect1>
 316     <title>See Also</title>
 317     <para><simplelist type="inline">
 318       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 319       <member><citerefentry><refentrytitle>systemd-veritysetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 320       <member><citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 321       <member><citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 322       <member><citerefentry project='die-net'><refentrytitle>veritysetup</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 323     </simplelist></para>
 324   </refsect1>
 325
 326 </refentry>