man/hwdb.xml

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