man: document systemd-sysctl --save= and --revert=

man/systemd-sysctl.service.xml

@@ -110,6 +110,31 @@
         <xi:include href="version-info.xml" xpointer="v259"/></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>--save=<replaceable>FILENAME</replaceable></option></term>
+        <listitem>
+          <para>Before applying the loaded sysctl settings, write them to <filename>/run/sysctl.d/</filename>
+          using the specified filename. If the filename does not end with <filename>.conf</filename>, the
+          suffix is appended. This option requires one or more positional arguments. May be combined with
+          <option>--inline</option>. This may be useful for creating runtime sysctl configuration files or
+          overriding existing sysctl configuration files.</para>
+
+          <xi:include href="version-info.xml" xpointer="v262"/>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><option>--revert=<replaceable>FILENAME</replaceable></option></term>
+        <listitem>
+          <para>Before loading and applying the sysctl settings, removes the specified sysctl configuration
+          file under <filename>/run/sysctl.d/</filename>. If the filename does not end with
+          <filename>.conf</filename>, the suffix is appended. This may be useful for removing configuration
+          files created by <option>--save=</option>.</para>
+
+          <xi:include href="version-info.xml" xpointer="v262"/>
+        </listitem>
+      </varlistentry>
+
       <xi:include href="standard-options.xml" xpointer="cat-config" />
       <xi:include href="standard-options.xml" xpointer="tldr" />
       <xi:include href="standard-options.xml" xpointer="no-pager" />
@@ -186,6 +211,26 @@ kernel.core_pattern = |/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t %P %I
       of preference.</para>
     </example>
 
+    <example>
+      <title>Disable IPv6 on an interface and save the specified setting</title>
+
+      <programlisting># /usr/lib/systemd/systemd-sysctl --save=99-disable-ipv6-foo - &lt;&lt;EOF
+net.ipv6.conf.foo.disable_ipv6=1
+EOF</programlisting>
+
+      <para>This disables IPv6 on the network interface <filename>foo</filename>, and creates
+      <filename>/run/sysctl.d/99-disable-ipv6-foo.conf</filename>.</para>
+    </example>
+
+    <example>
+      <title>Remove a runtime sysctl configuration file</title>
+
+      <programlisting># /usr/lib/systemd/systemd-sysctl --revert=99-disable-ipv6-foo --prefix=/net/ipv6/conf/foo</programlisting>
+
+      <para>This removes <filename>/run/sysctl.d/99-disable-ipv6-foo.conf</filename>, and applies the
+      remaining sysctl settings for the network interface <filename>foo</filename>.</para>
+    </example>
+
     <para>See
     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
     for various ways to directly apply sysctl settings.</para>