man/hwdb.xml

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   8   Copyright © 2014 Tom Gundersen
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  10
  11 <refentry id="hwdb" conditional="ENABLE_HWDB">
  12   <refentryinfo>
  13     <title>hwdb</title>
  14     <productname>systemd</productname>
  15   </refentryinfo>
  16
  17   <refmeta>
  18     <refentrytitle>hwdb</refentrytitle>
  19     <manvolnum>7</manvolnum>
  20   </refmeta>
  21
  22   <refnamediv>
  23     <refname>hwdb</refname>
  24     <refpurpose>Hardware Database</refpurpose>
  25   </refnamediv>
  26
  27   <refsect1><title>Description</title>
  28     <para>The hardware database is a key-value store for associating modalias-like keys to
  29     udev-property-like values. It is used primarily by udev to add the relevant properties
  30     to matching devices, but it can also be queried directly.</para>
  31   </refsect1>
  32
  33   <refsect1><title>Hardware Database Files</title>
  34       <para>The hwdb files are read from the files located in the
  35       system hwdb directory <filename>/usr/lib/udev/hwdb.d</filename> and
  36       the local administration directory <filename>/etc/udev/hwdb.d</filename>.
  37       All hwdb files are collectively sorted and processed in lexical order,
  38       regardless of the directories in which they live. However, files with
  39       identical filenames replace each other. Files in <filename>/etc</filename>
  40       have the highest priority and take precedence over files with the same
  41       name in <filename>/usr/lib</filename>. This can be used to override a
  42       system-supplied hwdb file with a local file if needed;
  43       a symlink in <filename>/etc</filename> with the same name as a hwdb file in
  44       <filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,
  45       disables that hwdb file entirely. hwdb files must have the extension
  46       <filename>.hwdb</filename>; other extensions are ignored.</para>
  47
  48       <para>Each hwdb file contains data records consisting of matches and associated
  49       key-value pairs. Every record in the hwdb starts with one or more match strings,
  50       specifying a shell glob to compare the lookup string against. Multiple match lines
  51       are specified in consecutive lines. Every match line is compared individually, and
  52       they are combined by OR. Every match line must start at the first character of the
  53       line.</para>
  54
  55       <para>The match lines are followed by one or more key-value pair lines, which are
  56       recognized by a leading space character. The key name and value are separated by
  57       <literal>=</literal>. An empty line signifies the end of a record. Lines beginning
  58       with <literal>#</literal> are ignored.</para>
  59
  60       <para>In case multiple records match a given lookup string, the key-value pairs
  61       from all records are combined. If a key is specified multiple times, the value
  62       from the record with the highest priority is used (each key can have only a single
  63       value). The priority is higher when the record is in a file that sorts later
  64       lexicographically, and in case of records in the same file, later records have
  65       higher priority.</para>
  66
  67       <para>The content of all hwdb files is read by
  68       <citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  69       and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>,
  70       or alternatively <filename>/usr/lib/udev/hwdb.bin</filename> if you want ship the
  71       compiled database in an immutable image.  During runtime, only the binary database
  72       is used.</para>
  73   </refsect1>
  74
  75   <refsect1>
  76     <title>Examples</title>
  77
  78     <example>
  79       <title>General syntax of hwdb files</title>
  80
  81       <programlisting># /usr/lib/udev/hwdb.d/example.hwdb
  82 # Comments can be placed before any records. This is a good spot
  83 # to describe what that file is used for, what kind of properties
  84 # it defines, and the ordering convention.
  85
  86 # A record with three matches and one property
  87 mouse:*:name:*Trackball*:
  88 mouse:*:name:*trackball*:
  89 mouse:*:name:*TrackBall*:
  90  ID_INPUT_TRACKBALL=1
  91
  92 # A record with a single match and five properties
  93 mouse:usb:v046dp4041:name:Logitech MX Master:
  94  MOUSE_DPI=1000@166
  95  MOUSE_WHEEL_CLICK_ANGLE=15
  96  MOUSE_WHEEL_CLICK_ANGLE_HORIZONTAL=26
  97  MOUSE_WHEEL_CLICK_COUNT=24
  98  MOUSE_WHEEL_CLICK_COUNT_HORIZONTAL=14
  99 </programlisting>
 100     </example>
 101
 102     <example>
 103       <title>Overriding of properties</title>
 104
 105       <programlisting># /usr/lib/udev/hwdb.d/60-keyboard.hwdb
 106 evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn*
 107  KEYBOARD_KEY_a1=help
 108  KEYBOARD_KEY_a2=setup
 109  KEYBOARD_KEY_a3=battery
 110
 111 evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn123*
 112  KEYBOARD_KEY_a2=wlan
 113
 114 # /etc/udev/hwdb.d/70-keyboard.hwdb
 115 # disable wlan key on all at keyboards
 116 evdev:atkbd:*
 117  KEYBOARD_KEY_a2=reserved</programlisting>
 118
 119       <para>If the hwdb consists of those two files, a keyboard with the lookup string
 120       <literal>evdev:atkbd:dmi:bvnAcer:bdXXXXX:bd08/05/2010:svnAcer:pn123</literal>
 121       will match all three records, and end up with the following properties:</para>
 122
 123       <programlisting>KEYBOARD_KEY_a1=help
 124 KEYBOARD_KEY_a2=reserved
 125 KEYBOARD_KEY_a3=battery</programlisting>
 126     </example>
 127   </refsect1>
 128
 129   <refsect1>
 130     <title>See Also</title>
 131     <para>
 132       <citerefentry>
 133         <refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum>
 134       </citerefentry>
 135     </para>
 136   </refsect1>
 137 </refentry>