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<refentry id="hwdb" conditional="ENABLE_HWDB">

<refentryinfo>

<title>hwdb</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Kay</firstname>

<surname>Sievers</surname>

<email>kay@vrfy.org</email>

</author>

<author>

<contrib>Developer</contrib>

<firstname>Tom</firstname>

<surname>Gundersen</surname>

<email>teg@jklm.no</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>hwdb</refentrytitle>

<manvolnum>7</manvolnum>

</refmeta>

<refnamediv>

<refname>hwdb</refname>

<refpurpose>Hardware Database</refpurpose>

</refnamediv>

<refsect1><title>Description</title>

<para>The hardware database is a key-value store for associating modalias-like keys to

udev-properties-like values. It is used primarily by udev to add the relevant properties

to matching devices, but it can also be queried directly.</para>

</refsect1>

<refsect1><title>Hardware Database Files</title>

<para>The hwdb files are read from the files located in the

system hwdb directory <filename>&udevlibexecdir;/hwdb.d</filename>,

the volatile runtime directory <filename>/run/udev/hwdb.d</filename>

and the local administration directory <filename>/etc/udev/hwdb.d</filename>.

All hwdb files are collectively sorted and processed in lexical order,

regardless of the directories in which they live. However, files with

identical filenames replace each other. Files in <filename>/etc</filename>

have the highest priority, files in <filename>/run</filename> take precedence

over files with the same name in <filename>/usr/lib</filename>. This can be

used to override a system-supplied hwdb file with a local file if needed;

a symlink in <filename>/etc</filename> with the same name as a hwdb file in

<filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,

disables the hwdb file entirely. hwdb files must have the extension

<filename>.hwdb</filename>; other extensions are ignored.</para>

<para>The hwdb file contains data records consisting of matches and

associated key-value pairs. Every record in the hwdb starts with one or

more match string, specifying a shell glob to compare the database

lookup string against. Multiple match lines are specified in additional

consecutive lines. Every match line is compared individually, they are

combined by OR. Every match line must start at the first character of

the line.</para>

<para>The match lines are followed by one or more key-value pair lines, which

are recognized by a leading space character. The key name and value are separated

by <literal>=</literal>. An empty line signifies the end

of a record. Lines beginning with <literal>#</literal> are ignored.</para>

<para>The content of all hwdb files is read by

<citerefentry><refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum></citerefentry>

and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>,

or alternatively <filename>&udevlibexecdir;/hwdb.bin</filename> if you want ship the compiled

database in an immutable image.

During runtime only the binary database is used.</para>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry>

<refentrytitle>systemd-hwdb</refentrytitle><manvolnum>8</manvolnum>

</citerefentry>

</para>

</refsect1>

</refentry>