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-or-later -->
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>Match patterns consist of literal characters, and shell-style wildcards:</para>
51      <itemizedlist>
52        <listitem><para>Asterisk <literal>*</literal> matches any number of characters
53        </para></listitem>
54        <listitem><para>Question mark <literal>?</literal> matches a single character
55        </para></listitem>
56        <listitem><para>Character list <literal>[<replaceable>chars</replaceable>]</literal> matches one of
57        the characters <replaceable>chars</replaceable> listed between <literal>[</literal> and
58        <literal>]</literal>. A range may be specified as with a dash as
59        <literal>[<replaceable>first</replaceable>-<replaceable>last</replaceable>]</literal>. The match may
60        be inverted with a caret <literal>[^…]</literal>.</para></listitem>
61      </itemizedlist>
62
63      <para>The match lines are followed by one or more key-value pair lines, which are
64      recognized by a leading space character. The key name and value are separated by
65      <literal>=</literal>. An empty line signifies the end of a record. Lines beginning
66      with <literal>#</literal> are ignored.</para>
67
68      <para>In case multiple records match a given lookup string, the key-value pairs
69      from all records are combined. If a key is specified multiple times, the value
70      from the record with the highest priority is used (each key can have only a single
71      value). The priority is higher when the record is in a file that sorts later
72      lexicographically, and in case of records in the same file, later records have
73      higher priority.</para>
74
75      <para>The content of all hwdb files is read by
76      <citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
77      and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>,
78      or alternatively <filename>/usr/lib/udev/hwdb.bin</filename> if you want ship the
79      compiled database in an immutable image.  During runtime, only the binary database
80      is used.</para>
81  </refsect1>
82
83  <refsect1>
84    <title>Examples</title>
85
86    <example>
87      <title>General syntax of hwdb files</title>
88
89      <programlisting># /usr/lib/udev/hwdb.d/example.hwdb
90# Comments can be placed before any records. This is a good spot
91# to describe what that file is used for, what kind of properties
92# it defines, and the ordering convention.
93
94# A record with three matches and one property
95mouse:*:name:*Trackball*:*
96mouse:*:name:*trackball*:*
97mouse:*:name:*TrackBall*:*
98 ID_INPUT_TRACKBALL=1
99
100# The rule above could be also be written in a form that
101# matches Tb, tb, TB, tB:
102mouse:*:name:*[tT]rack[bB]all*:*
103 ID_INPUT_TRACKBALL=1
104
105# A record with a single match and five properties
106mouse:usb:v046dp4041:name:Logitech MX Master:*
107 MOUSE_DPI=1000@166
108 MOUSE_WHEEL_CLICK_ANGLE=15
109 MOUSE_WHEEL_CLICK_ANGLE_HORIZONTAL=26
110 MOUSE_WHEEL_CLICK_COUNT=24
111 MOUSE_WHEEL_CLICK_COUNT_HORIZONTAL=14
112</programlisting>
113    </example>
114
115    <example>
116      <title>Overriding of properties</title>
117
118      <programlisting># /usr/lib/udev/hwdb.d/60-keyboard.hwdb
119evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn*:*
120 KEYBOARD_KEY_a1=help
121 KEYBOARD_KEY_a2=setup
122 KEYBOARD_KEY_a3=battery
123
124# Match vendor name "Acer" and any product name starting with "X123"
125evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer:pnX123*:*
126 KEYBOARD_KEY_a2=wlan
127
128# /etc/udev/hwdb.d/70-keyboard.hwdb
129# disable wlan key on all at keyboards
130evdev:atkbd:*
131 KEYBOARD_KEY_a2=reserved
132 PROPERTY_WITH_SPACES=some string</programlisting>
133
134      <para>If the hwdb consists of those two files, a keyboard with the lookup string
135      <literal>evdev:atkbd:dmi:bvnAcer:bdXXXXX:bd08/05/2010:svnAcer:pnX123</literal>
136      will match all three records, and end up with the following properties:</para>
137
138      <programlisting>KEYBOARD_KEY_a1=help
139KEYBOARD_KEY_a2=reserved
140KEYBOARD_KEY_a3=battery
141PROPERTY_WITH_SPACES=some string</programlisting>
142
143    </example>
144  </refsect1>
145
146  <refsect1>
147    <title>See Also</title>
148    <para>
149      <citerefentry>
150        <refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum>
151      </citerefentry>
152    </para>
153  </refsect1>
154</refentry>
155