man/hwdb.xml

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   8 <refentry id="hwdb" conditional="ENABLE_HWDB">
   9   <refentryinfo>
  10     <title>hwdb</title>
  11     <productname>systemd</productname>
  12     <authorgroup>
  13       <author>
  14         <contrib>Developer</contrib>
  15         <firstname>Kay</firstname>
  16         <surname>Sievers</surname>
  17         <email>kay@vrfy.org</email>
  18       </author>
  19       <author>
  20         <contrib>Developer</contrib>
  21         <firstname>Tom</firstname>
  22         <surname>Gundersen</surname>
  23         <email>teg@jklm.no</email>
  24       </author>
  25     </authorgroup>
  26   </refentryinfo>
  27
  28   <refmeta>
  29     <refentrytitle>hwdb</refentrytitle>
  30     <manvolnum>7</manvolnum>
  31   </refmeta>
  32
  33   <refnamediv>
  34     <refname>hwdb</refname>
  35     <refpurpose>Hardware Database</refpurpose>
  36   </refnamediv>
  37
  38   <refsect1><title>Description</title>
  39     <para>The hardware database is a key-value store for associating modalias-like keys to
  40     udev-properties-like values. It is used primarily by udev to add the relevant properties
  41     to matching devices, but it can also be queried directly.</para>
  42   </refsect1>
  43
  44   <refsect1><title>Hardware Database Files</title>
  45       <para>The hwdb files are read from the files located in the
  46       system hwdb directory <filename>&udevlibexecdir;/hwdb.d</filename>,
  47       the volatile runtime directory <filename>/run/udev/hwdb.d</filename>
  48       and the local administration directory <filename>/etc/udev/hwdb.d</filename>.
  49       All hwdb files are collectively sorted and processed in lexical order,
  50       regardless of the directories in which they live. However, files with
  51       identical filenames replace each other. Files in <filename>/etc</filename>
  52       have the highest priority, files in <filename>/run</filename> take precedence
  53       over files with the same name in <filename>&rootprefix;/lib</filename>. This can be
  54       used to override a system-supplied hwdb file with a local file if needed;
  55       a symlink in <filename>/etc</filename> with the same name as a hwdb file in
  56       <filename>&rootprefix;/lib</filename>, pointing to <filename>/dev/null</filename>,
  57       disables the hwdb file entirely. hwdb files must have the extension
  58       <filename>.hwdb</filename>; other extensions are ignored.</para>
  59
  60       <para>The hwdb file contains data records consisting of matches and
  61       associated key-value pairs. Every record in the hwdb starts with one or
  62       more match string, specifying a shell glob to compare the database
  63       lookup string against. Multiple match lines are specified in additional
  64       consecutive lines. Every match line is compared individually, they are
  65       combined by OR. Every match line must start at the first character of
  66       the line.</para>
  67
  68       <para>The match lines are followed by one or more key-value pair lines, which
  69       are recognized by a leading space character. The key name and value are separated
  70       by <literal>=</literal>. An empty line signifies the end
  71       of a record. Lines beginning with <literal>#</literal> are ignored.</para>
  72
  73       <para>The content of all hwdb files is read by
  74       <citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  75       and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>,
  76       or alternatively <filename>&udevlibexecdir;/hwdb.bin</filename> if you want ship the compiled
  77       database in an immutable image.
  78       During runtime only the binary database is used.</para>
  79   </refsect1>
  80
  81   <refsect1>
  82     <title>See Also</title>
  83     <para>
  84       <citerefentry>
  85         <refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum>
  86       </citerefentry>
  87     </para>
  88   </refsect1>
  89 </refentry>