man/hwdb.xml

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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright © 2014 Tom Gundersen
   9 -->
  10
  11 <refentry id="hwdb" conditional="ENABLE_HWDB">
  12   <refentryinfo>
  13     <title>hwdb</title>
  14     <productname>systemd</productname>
  15     <authorgroup>
  16       <author>
  17         <contrib>Developer</contrib>
  18         <firstname>Kay</firstname>
  19         <surname>Sievers</surname>
  20         <email>kay@vrfy.org</email>
  21       </author>
  22       <author>
  23         <contrib>Developer</contrib>
  24         <firstname>Tom</firstname>
  25         <surname>Gundersen</surname>
  26         <email>teg@jklm.no</email>
  27       </author>
  28     </authorgroup>
  29   </refentryinfo>
  30
  31   <refmeta>
  32     <refentrytitle>hwdb</refentrytitle>
  33     <manvolnum>7</manvolnum>
  34   </refmeta>
  35
  36   <refnamediv>
  37     <refname>hwdb</refname>
  38     <refpurpose>Hardware Database</refpurpose>
  39   </refnamediv>
  40
  41   <refsect1><title>Description</title>
  42     <para>The hardware database is a key-value store for associating modalias-like keys to
  43     udev-property-like values. It is used primarily by udev to add the relevant properties
  44     to matching devices, but it can also be queried directly.</para>
  45   </refsect1>
  46
  47   <refsect1><title>Hardware Database Files</title>
  48       <para>The hwdb files are read from the files located in the
  49       system hwdb directory <filename>/usr/lib/udev/hwdb.d</filename> and
  50       the local administration directory <filename>/etc/udev/hwdb.d</filename>.
  51       All hwdb files are collectively sorted and processed in lexical order,
  52       regardless of the directories in which they live. However, files with
  53       identical filenames replace each other. Files in <filename>/etc</filename>
  54       have the highest priority and take precedence over files with the same
  55       name in <filename>/usr/lib</filename>. This can be used to override a
  56       system-supplied hwdb file with a local file if needed;
  57       a symlink in <filename>/etc</filename> with the same name as a hwdb file in
  58       <filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,
  59       disables that hwdb file entirely. hwdb files must have the extension
  60       <filename>.hwdb</filename>; other extensions are ignored.</para>
  61
  62       <para>Each hwdb file contains data records consisting of matches and associated
  63       key-value pairs. Every record in the hwdb starts with one or more match strings,
  64       specifying a shell glob to compare the lookup string against. Multiple match lines
  65       are specified in consecutive lines. Every match line is compared individually, and
  66       they are combined by OR. Every match line must start at the first character of the
  67       line.</para>
  68
  69       <para>The match lines are followed by one or more key-value pair lines, which are
  70       recognized by a leading space character. The key name and value are separated by
  71       <literal>=</literal>. An empty line signifies the end of a record. Lines beginning
  72       with <literal>#</literal> are ignored.</para>
  73
  74       <para>In case multiple records match a given lookup string, the key-value pairs
  75       from all records are combined. If a key is specified multiple times, the value
  76       from the record with the highest priority is used (each key can have only a single
  77       value). The priority is higher when the record is in a file that sorts later
  78       lexicographically, and in case of records in the same file, later records have
  79       higher priority.</para>
  80
  81       <para>The content of all hwdb files is read by
  82       <citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  83       and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>,
  84       or alternatively <filename>/usr/lib/udev/hwdb.bin</filename> if you want ship the
  85       compiled database in an immutable image.  During runtime, only the binary database
  86       is used.</para>
  87   </refsect1>
  88
  89   <refsect1>
  90     <title>Examples</title>
  91
  92     <example>
  93       <title>General syntax of hwdb files</title>
  94
  95       <programlisting># /usr/lib/udev/hwdb.d/example.hwdb
  96 # Comments can be placed before any records. This is a good spot
  97 # to describe what that file is used for, what kind of properties
  98 # it defines, and the ordering convention.
  99
 100 # A record with three matches and one property
 101 mouse:*:name:*Trackball*:
 102 mouse:*:name:*trackball*:
 103 mouse:*:name:*TrackBall*:
 104  ID_INPUT_TRACKBALL=1
 105
 106 # A record with a single match and five properties
 107 mouse:usb:v046dp4041:name:Logitech MX Master:
 108  MOUSE_DPI=1000@166
 109  MOUSE_WHEEL_CLICK_ANGLE=15
 110  MOUSE_WHEEL_CLICK_ANGLE_HORIZONTAL=26
 111  MOUSE_WHEEL_CLICK_COUNT=24
 112  MOUSE_WHEEL_CLICK_COUNT_HORIZONTAL=14
 113 </programlisting>
 114     </example>
 115
 116     <example>
 117       <title>Overriding of properties</title>
 118
 119       <programlisting># /usr/lib/udev/hwdb.d/60-keyboard.hwdb
 120 evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn*
 121  KEYBOARD_KEY_a1=help
 122  KEYBOARD_KEY_a2=setup
 123  KEYBOARD_KEY_a3=battery
 124
 125 evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn123*
 126  KEYBOARD_KEY_a2=wlan
 127
 128 # /etc/udev/hwdb.d/70-keyboard.hwdb
 129 # disable wlan key on all at keyboards
 130 evdev:atkbd:*
 131  KEYBOARD_KEY_a2=reserved</programlisting>
 132
 133       <para>If the hwdb consists of those two files, a keyboard with the lookup string
 134       <literal>evdev:atkbd:dmi:bvnAcer:bdXXXXX:bd08/05/2010:svnAcer:pn123</literal>
 135       will match all three records, and end up with the following properties:</para>
 136
 137       <programlisting>KEYBOARD_KEY_a1=help
 138 KEYBOARD_KEY_a2=reserved
 139 KEYBOARD_KEY_a3=battery</programlisting>
 140     </example>
 141   </refsect1>
 142
 143   <refsect1>
 144     <title>See Also</title>
 145     <para>
 146       <citerefentry>
 147         <refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum>
 148       </citerefentry>
 149     </para>
 150   </refsect1>
 151 </refentry>