- <title>Configuration Format</title>
-
- <para>The configuration files should simply contain a
- list of variable assignments, separated by
- newlines. Empty lines and lines whose first
- non-whitespace character is # or ; are ignored.</para>
-
- <para>Note that both / and . are accepted as
- separators in sysctl variable names.</para>
-
+ <title>Configuration Format</title>
+
+ <para>The configuration files contain a list of
+ variable assignments, separated by newlines. Empty
+ lines and lines whose first non-whitespace character
+ is # or ; are ignored.</para>
+
+ <para>Note that both / and . are accepted as label
+ separators within sysctl variable
+ names. <literal>kernel.domainname=foo</literal> and
+ <literal>kernel/domainname=foo</literal> hence are
+ entirely equivalent.</para>
+
+ <para>Each configuration file shall be named in the
+ style of <filename><replaceable>program</replaceable>.conf</filename>.
+ Files in <filename>/etc/</filename> override files
+ with the same name in <filename>/usr/lib/</filename>
+ and <filename>/run/</filename>. Files in
+ <filename>/run/</filename> override files with the same
+ name in <filename>/usr/lib/</filename>. Packages
+ should install their configuration files in
+ <filename>/usr/lib/</filename>. Files in
+ <filename>/etc/</filename> are reserved for the local
+ administrator, who may use this logic to override the
+ configuration files installed by vendor packages. All
+ configuration files are sorted by their filename in
+ lexicographic order, regardless of which of the
+ directories they reside in. If multiple files specify the
+ same variable name, the entry in the file with the
+ lexicographically latest name will be applied. It is
+ recommended to prefix all filenames with a two-digit
+ number and a dash, to simplify the ordering of the
+ files.</para>
+
+ <para>If the administrator wants to disable a
+ configuration file supplied by the vendor, the
+ recommended way is to place a symlink to
+ <filename>/dev/null</filename> in
+ <filename>/etc/sysctl.d/</filename> bearing the
+ same filename.</para>