XEN: How to boot SLES 12 para-virtual DomU's into the Rescue System for disaster recovery.

1.    Download the DVD for SLES 12 SP1 from download.suse.com

2.    Mount the the ISO

        mount -o loop /root/SLE-12-SP1-Server-DVD-x86_64-GM-DVD1.iso /mnt

3.    Change directory to the boot loader location on the mounted ISO image.

        cd /mnt/boot/x86_64

4.    Create a directory e.g. in /etc/xen to store the kernel and the RAM disk that will be used to boot the problematic DomU.

        mkdir /etc/xen/rescue-sles12

5.    Copy the kernel and the RAM disk to the temporary location.

        cp /mnt/boot/x86_64/vmlinuz-xen /etc/xen/rescue-sles12
        cp /mnt/boot/x86_64/initrd-xen /etc/xen/rescue-sles12

6.    Umount the ISO image.

        umount /mnt

7.    Go to /etc/libvirt/libxl

When the installation file that was used to create the DomU is there, create a copy of it.
If you do not have a copy, you may use the example at the bottom of this TID; copy and edit as needed.

8.    Open the copy for editing. DO NOT EDIT THE ORIGINAL FILE

        cp <NAME_OF_VM> sles12-rescue

9.     Remove the line with UUID

10.    Comment out the bootloader and bootloader_args lines

11.    Change the "name=" directive. If you don't, the DomU will not boot. For example, change it to:

        name="rescue-sles12"

12.    Locate the tag "<disk"... It may look like this:

        <disk type='file' device='disk'>
          <driver name='qemu' type='raw'/>
          <source file='.../sles12.img'/>
          <target dev='xvda' bus='xen'/>
        </disk>

13. In order to add the rescue DVD to the DomU and use it for the rescue system add another disk pointing to the iso image:

        <disk device="cdrom" type="file">
          <driver name="file" />
          <source file=".../SLE-12-SP1-Server-DVD-x86_64-GM-DVD1.iso" />
          <target dev="xvdh" />
          <readonly />
        </disk>

14.    The following will direct Xen to load the kernel and the RAM disk from /etc/xen/rescue12, and then to load the rescue system from the CD.

        <os>
          <type arch="x86_64" machine="xenpv">linux</type>
          <kernel>/etc/xen/rescue-sles12/vmlinuz-xen</kernel>
          <initrd>/etc/xen/rescue-sles12/initrd-xen</initrd>
          <cmdline> install=hd:xvdh rescue=1</cmdline>
        </os>

15.    Save and close the file

16.    Boot the rescue system.
    Since this is a rescue DomU, use the "virsh create" command. The configuration will not be saved after the DomU is shutdown
        virsh create /root/sles12-rescue.xml

17.    Perform the rescue steps that need to be done inside the DomU

18.    Shutdown the DomU

19.    Start the DomU normally with out using the rescue configuration file to make sure that it will start

example rescue configuration file

<domain type="xen">
  <name>rescue-system</name>
  <memory unit="KiB">2621440</memory>
  <currentMemory unit="KiB">2621440</currentMemory>
  <vcpu placement="static">1</vcpu>
  <os>
    <type arch="x86_64" machine="xenpv">linux</type>
    <kernel>/etc/xen/rescue-sles12/vmlinuz-xen</kernel>
    <initrd>/etc/xen/rescue-sles12/initrd-xen</initrd>
    <cmdline> install=hd:xvdh rescue=1</cmdline>
  </os>
  <clock adjustment="reset" offset="utc" />
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <disk device="cdrom" type="file">
      <driver name="file" />
      <source file=".../SLE-12-SP1-Server-DVD-x86_64-GM-DVD1.iso" />
      <target dev="xvdh" />
      <readonly />
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='.../sles12.img'/>
      <target dev='xvda' bus='xen'/>
    </disk>
    <console type="pty">
      <target port="0" type="xen" />
    </console>
    <input type="mouse" />
    <input type="keyboard" />
    <graphics autoport="yes" port="-1" type="vnc" />
  </devices>
</domain>