Manual: Add paragraph on xserver keyboard layout

Changed files
+7
nixos
doc
manual
configuration
+7
nixos/doc/manual/configuration/x-windows.xml
···
</programlisting>
</para>
+
<para>You can set the keyboard layout (and optionally the layout variant):
+
<programlisting>
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services.xserver.layout = "de";
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services.xserver.xkbVariant = "neo";
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</programlisting>
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</para>
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<para>The X server is started automatically at boot time. If you
don’t want this to happen, you can set:
<programlisting>