man/veritytab.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-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 integrity 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 integrity 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> <replaceable>options</replaceable></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     <literal>UUID=</literal> followed by the UUID.</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     <literal>UUID=</literal> followed by the UUID.</para>
  55
  56     <para>The fourth field is the <literal>roothash</literal> 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>ignore-corruption</option></term>
  65         <term><option>restart-on-corruption</option></term>
  66         <term><option>panic-on-corruption</option></term>
  67
  68         <listitem><para>Defines what to do if data integrity problem is detected (data corruption). Without these
  69         options kernel fails the IO operation with I/O error. With <literal>--ignore-corruption</literal> option the
  70         corruption is only logged. With <literal>--restart-on-corruption</literal> or
  71         <literal>--panic-on-corruption</literal> the kernel is restarted (panicked) immediately.
  72
  73         (You have to provide way how to avoid restart loops.)</para></listitem>
  74       </varlistentry>
  75
  76       <varlistentry>
  77         <term><option>ignore-zero-blocks</option></term>
  78
  79         <listitem><para>Instruct kernel to not verify blocks that are expected to contain zeroes and always directly
  80         return zeroes instead.
  81
  82         WARNING: Use this option only in very specific cases. This option is available since Linux kernel version 4.5.
  83         </para></listitem>
  84       </varlistentry>
  85
  86       <varlistentry>
  87         <term><option>check-at-most-once</option></term>
  88
  89         <listitem><para>Instruct kernel to verify blocks only the first time they are read from the data device, rather
  90         than every time.
  91
  92         WARNING: It provides a reduced level of security because only offline tampering of the data device's content
  93         will be detected, not online tampering. This option is available since Linux kernel version 4.17.
  94         </para></listitem>
  95       </varlistentry>
  96
  97       <varlistentry>
  98         <term><option>root-hash-signature=</option></term>
  99
 100         <listitem><para>A base64 string encoding the root hash signature prefixed by <literal>base64:</literal> or a
 101         path to roothash signature file used to verify the root hash (in kernel). This feature requires Linux kernel
 102         version 5.4 or more recent.</para></listitem>
 103       </varlistentry>
 104
 105       <varlistentry>
 106         <term><option>_netdev</option></term>
 107
 108         <listitem><para>Marks this veritysetup device as requiring network. It will be
 109         started after the network is available, similarly to
 110         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 111         units marked with <option>_netdev</option>. The service unit to set up this device
 112         will be ordered between <filename>remote-fs-pre.target</filename> and
 113         <filename>remote-veritysetup.target</filename>, instead of
 114         <filename>veritysetup-pre.target</filename> and
 115         <filename>veritysetup.target</filename>.</para>
 116
 117         <para>Hint: if this device is used for a mount point that is specified in
 118         <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 119         the <option>_netdev</option> option should also be used for the mount
 120         point. Otherwise, a dependency loop might be created where the mount point
 121         will be pulled in by <filename>local-fs.target</filename>, while the
 122         service to configure the network is usually only started <emphasis>after</emphasis>
 123         the local file system has been mounted.</para>
 124         </listitem>
 125       </varlistentry>
 126
 127       <varlistentry>
 128         <term><option>noauto</option></term>
 129
 130         <listitem><para>This device will not be added to <filename>veritysetup.target</filename>.
 131         This means that it will not be automatically enabled on boot, unless something else pulls
 132         it in. In particular, if the device is used for a mount point, it'll be enabled
 133         automatically during boot, unless the mount point itself is also disabled with
 134         <option>noauto</option>.</para></listitem>
 135       </varlistentry>
 136
 137       <varlistentry>
 138         <term><option>nofail</option></term>
 139
 140         <listitem><para>This device will not be a hard dependency of
 141         <filename>veritysetup.target</filename>. It'll still be pulled in and started, but the system
 142         will not wait for the device to show up and be enabled, and boot will not fail if this is
 143         unsuccessful. Note that other units that depend on the enabled device may still fail. In
 144         particular, if the device is used for a mount point, the mount point itself also needs to
 145         have the <option>nofail</option> option, or the boot will fail if the device is not enabled
 146         successfully.</para></listitem>
 147       </varlistentry>
 148
 149       <varlistentry>
 150         <term><option>x-initrd.attach</option></term>
 151
 152         <listitem><para>Setup this verity integrity protected block device in the initramfs, similarly to
 153         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 154         units marked with <option>x-initrd.mount</option>.</para>
 155
 156         <para>Although it's not necessary to mark the mount entry for the root file system with
 157         <option>x-initrd.mount</option>, <option>x-initrd.attach</option> is still recommended with
 158         the verity integrity protected block device containing the root file system as otherwise systemd
 159         will attempt to detach the device during the regular system shutdown while it's still in
 160         use. With this option the device will still be detached but later after the root file
 161         system is unmounted.</para>
 162
 163         <para>All other verity integrity protected block devices that contain file systems mounted in the
 164         initramfs should use this option.</para>
 165         </listitem>
 166       </varlistentry>
 167
 168     </variablelist>
 169
 170     <para>At early boot and when the system manager configuration is
 171     reloaded, this file is translated into native systemd units by
 172     <citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 173   </refsect1>
 174
 175   <refsect1>
 176     <title>Examples</title>
 177     <example>
 178       <title>/etc/veritytab example</title>
 179       <para>Set up two verity integrity protected block devices. One using device blocks, another using files.</para>
 180
 181       <programlisting>usr  PARTUUID=783e45ae-7aa3-484a-beef-a80ff9c19cbb PARTUUID=21dc1dfe-4c33-8b48-98a9-918a22eb3e37 36e3f740ad502e2c25e2a23d9c7c17bf0fdad2300b7580842d4b7ec1fb0fa263 auto
 182 data /etc/data /etc/hash a5ee4b42f70ae1f46a08a7c92c2e0a20672ad2f514792730f5d49d7606ab8fdf auto
 183 </programlisting>
 184     </example>
 185   </refsect1>
 186
 187   <refsect1>
 188     <title>See Also</title>
 189     <para>
 190       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 191       <citerefentry><refentrytitle>systemd-veritysetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 192       <citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 193       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 194       <citerefentry project='die-net'><refentrytitle>veritysetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 195     </para>
 196   </refsect1>
 197
 198 </refentry>