Fix for bsc #1069905

update kexec usage

xml/tuning_kexec.xml

@@ -536,83 +536,53 @@ cio_ignore=all,!da5d,!f500-f502</screen>
   <title>Basic &kexec; Usage</title>
 
   <para>
-   To verify if your &kexec; environment works properly, follow these
-   steps:
+   To use &kexec;, ensure the respective service is enabled and running:
   </para>
 
-  <procedure>
-   <step>
-    <para>
-     Make sure no users are currently logged in and no important services
-     are running on the system.
-    </para>
-   </step>
-   <step>
-    <para>
-     Log in as &rootuser;.
-    </para>
-   </step>
-   <step>
-    <para>
-     Switch to the rescue target with <command>systemctl isolate
-     rescue.target</command>
-    </para>
-   </step>
-   <step xml:id="step.kexec.usage.load.kernel">
-    <para>
-     Load the new kernel to the address space of the production kernel with
-     the following command:
-    </para>
-<screen>&prompt.root;<command>kexec</command> -l <replaceable>/boot/vmlinuz</replaceable> --append=<replaceable>"$(cat /proc/cmdline)"</replaceable> \
---initrd=<replaceable>/boot/initrd</replaceable></screen>
-   </step>
-   <step>
-    <para>
-     Unmount all mounted file systems except the root file system with:
-    </para>
-<screen><command>umount</command> <option>-a</option></screen>
-    <important>
-     <title>Unmounting the Root File System</title>
-     <para>
-      Unmounting all file systems will most likely produce a <literal>device
-      is busy</literal> warning message. The root file system cannot be
-      unmounted if the system is running. Ignore the warning.
-     </para>
-    </important>
-   </step>
-   <step>
+  <itemizedlist>
+   <listitem>
     <para>
-     Remount the root file system in read-only mode:
+     Make sure the &kexec; service is loaded at system start:
     </para>
-<screen>&prompt.root;<command>mount</command> -o remount,ro /</screen>
-   </step>
-   <step>
+    <screen>&prompt.sudo;systemctl enable kexec-load.service</screen>
+   </listitem>
+   <listitem>
     <para>
-     Initiate the reboot of the kernel that you loaded in
-     <xref linkend="step.kexec.usage.load.kernel"/> with:
+     Make sure the &kexec; service is running:
     </para>
-<screen>&prompt.root;<command>kexec</command> -e</screen>
-   </step>
-  </procedure>
+    <screen>&prompt.sudo;systemctl start kexec-load.service</screen>
+   </listitem>
+  </itemizedlist>
 
   <para>
-   It is important to unmount the previously mounted disk volumes in
-   read-write mode. The <systemitem>reboot</systemitem> system call acts
-   immediately upon calling. Hard disk volumes mounted in read-write mode
-   neither synchronize nor unmount automatically. The new kernel may find
-   them <quote>dirty</quote>. Read-only disk volumes and virtual file
-   systems do not need to be unmounted. Refer to
-   <filename>/etc/mtab</filename> to determine which file systems you need
-   to unmount.
+   To verify if your &kexec; environment works properly, try rebooting into a
+   new Kernel with &kexec;. Make sure no users are currently logged in and no
+   important services are running on the system. If this is the case, run the
+   following command:
   </para>
 
+  <screen>systemctl kexec</screen>
+
   <para>
    The new kernel previously loaded to the address space of the older kernel
    rewrites it and takes control immediately. It displays the usual start-up
    messages. When the new kernel boots, it skips all hardware and firmware
-   checks. Make sure no warning messages appear. All file systems are
-   supposed to be clean if they had been unmounted.
+   checks. Make sure no warning messages appear.
   </para>
+
+  <tip>
+   <title>Using &kexec; with the reboot command</title>
+   <para>
+    To make <command>reboot</command> use kexec; rather than performing a
+    regular reboot, run the following command:
+   </para>
+   <screen>ln -s /usr/lib/systemd/system/kexec.target /etc/systemd/system/reboot.target</screen>
+   <para>
+    You can revert this at any time by deleting
+    <filename>etc/systemd/system/reboot.target</filename>.
+   </para>
+  </tip>
+
  </sect1>
  <sect1 xml:id="cha.tuning.kexec.config">
   <title>How to Configure &kexec; for Routine Reboots</title>