man/hwdb.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="hwdb" conditional="ENABLE_HWDB">
   7   <refentryinfo>
   8     <title>hwdb</title>
   9     <productname>systemd</productname>
  10   </refentryinfo>
  11
  12   <refmeta>
  13     <refentrytitle>hwdb</refentrytitle>
  14     <manvolnum>7</manvolnum>
  15   </refmeta>
  16
  17   <refnamediv>
  18     <refname>hwdb</refname>
  19     <refpurpose>Hardware Database</refpurpose>
  20   </refnamediv>
  21
  22   <refsect1><title>Description</title>
  23     <para>The hardware database is a key-value store for associating modalias-like keys to
  24     udev-property-like values. It is used primarily by udev to add the relevant properties
  25     to matching devices, but it can also be queried directly.</para>
  26   </refsect1>
  27
  28   <refsect1><title>Hardware Database Files</title>
  29       <para>The hwdb files are read from the files located in the
  30       system hwdb directory <filename>/usr/lib/udev/hwdb.d</filename> and
  31       the local administration directory <filename>/etc/udev/hwdb.d</filename>.
  32       All hwdb files are collectively sorted and processed in lexical order,
  33       regardless of the directories in which they live. However, files with
  34       identical filenames replace each other. Files in <filename>/etc</filename>
  35       have the highest priority and take precedence over files with the same
  36       name in <filename>/usr/lib</filename>. This can be used to override a
  37       system-supplied hwdb file with a local file if needed;
  38       a symlink in <filename>/etc</filename> with the same name as a hwdb file in
  39       <filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,
  40       disables that hwdb file entirely. hwdb files must have the extension
  41       <filename>.hwdb</filename>; other extensions are ignored.</para>
  42
  43       <para>Each hwdb file contains data records consisting of matches and associated
  44       key-value pairs. Every record in the hwdb starts with one or more match strings,
  45       specifying a shell glob to compare the lookup string against. Multiple match lines
  46       are specified in consecutive lines. Every match line is compared individually, and
  47       they are combined by OR. Every match line must start at the first character of the
  48       line.</para>
  49
  50       <para>The match lines are followed by one or more key-value pair lines, which are
  51       recognized by a leading space character. The key name and value are separated by
  52       <literal>=</literal>. An empty line signifies the end of a record. Lines beginning
  53       with <literal>#</literal> are ignored.</para>
  54
  55       <para>In case multiple records match a given lookup string, the key-value pairs
  56       from all records are combined. If a key is specified multiple times, the value
  57       from the record with the highest priority is used (each key can have only a single
  58       value). The priority is higher when the record is in a file that sorts later
  59       lexicographically, and in case of records in the same file, later records have
  60       higher priority.</para>
  61
  62       <para>The content of all hwdb files is read by
  63       <citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  64       and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>,
  65       or alternatively <filename>/usr/lib/udev/hwdb.bin</filename> if you want ship the
  66       compiled database in an immutable image.  During runtime, only the binary database
  67       is used.</para>
  68   </refsect1>
  69
  70   <refsect1>
  71     <title>Examples</title>
  72
  73     <example>
  74       <title>General syntax of hwdb files</title>
  75
  76       <programlisting># /usr/lib/udev/hwdb.d/example.hwdb
  77 # Comments can be placed before any records. This is a good spot
  78 # to describe what that file is used for, what kind of properties
  79 # it defines, and the ordering convention.
  80
  81 # A record with three matches and one property
  82 mouse:*:name:*Trackball*:
  83 mouse:*:name:*trackball*:
  84 mouse:*:name:*TrackBall*:
  85  ID_INPUT_TRACKBALL=1
  86
  87 # A record with a single match and five properties
  88 mouse:usb:v046dp4041:name:Logitech MX Master:
  89  MOUSE_DPI=1000@166
  90  MOUSE_WHEEL_CLICK_ANGLE=15
  91  MOUSE_WHEEL_CLICK_ANGLE_HORIZONTAL=26
  92  MOUSE_WHEEL_CLICK_COUNT=24
  93  MOUSE_WHEEL_CLICK_COUNT_HORIZONTAL=14
  94 </programlisting>
  95     </example>
  96
  97     <example>
  98       <title>Overriding of properties</title>
  99
 100       <programlisting># /usr/lib/udev/hwdb.d/60-keyboard.hwdb
 101 evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn*
 102  KEYBOARD_KEY_a1=help
 103  KEYBOARD_KEY_a2=setup
 104  KEYBOARD_KEY_a3=battery
 105
 106 evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn123*
 107  KEYBOARD_KEY_a2=wlan
 108
 109 # /etc/udev/hwdb.d/70-keyboard.hwdb
 110 # disable wlan key on all at keyboards
 111 evdev:atkbd:*
 112  KEYBOARD_KEY_a2=reserved</programlisting>
 113
 114       <para>If the hwdb consists of those two files, a keyboard with the lookup string
 115       <literal>evdev:atkbd:dmi:bvnAcer:bdXXXXX:bd08/05/2010:svnAcer:pn123</literal>
 116       will match all three records, and end up with the following properties:</para>
 117
 118       <programlisting>KEYBOARD_KEY_a1=help
 119 KEYBOARD_KEY_a2=reserved
 120 KEYBOARD_KEY_a3=battery</programlisting>
 121     </example>
 122   </refsect1>
 123
 124   <refsect1>
 125     <title>See Also</title>
 126     <para>
 127       <citerefentry>
 128         <refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum>
 129       </citerefentry>
 130     </para>
 131   </refsect1>
 132 </refentry>