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systemd-stable/man/hwdb.xml
Tom Gundersen 12b42c7667 man: revert dynamic paths for split-usr setups
This did not really work out as we had hoped. Trying to do this upstream
introduced several problems that probably makes it better suited as a
downstream patch after all. At any rate, it is not releaseable in the
current state, so we at least need to revert this before the release.

 * by adjusting the path to binaries, but not do the same thing to the
   search path we end up with inconsistent man-pages. Adjusting the search
   path too would be quite messy, and it is not at all obvious that this is
   worth the effort, but at any rate it would have to be done before we
   could ship this.

 * this means that distributed man-pages does not make sense as they depend
   on config options, and for better or worse we are still distributing
   man pages, so that is something that definitely needs sorting out before
   we could ship with this patch.

 * we have long held that split-usr is only minimally supported in order
   to boot, and something we hope will eventually go away. So before we start
   adding even more magic/effort in order to make this work nicely, we should
   probably question if it makes sense at all.
2015-06-18 19:47:44 +02:00

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<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<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>/usr/lib/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 and 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>/usr/lib/udev/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>