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| <section id="update-iso-vm"> |
| <!-- CLOUDSTACK-667 --> |
| <title>Changing a VM's Base Image</title> |
| <para>Every VM is created from a base image, which is a template or ISO which has been created and |
| stored in &PRODUCT;. Both cloud administrators and end users can create and modify templates, |
| ISOs, and VMs.</para> |
| <para>In &PRODUCT;, you can change an existing VM's base image from one template to another, |
| or from one ISO to another. (You can not change from an ISO to a template, or from a |
| template to an ISO).</para> |
| <para>For example, suppose there is a |
| template based on a particular operating system, and the OS vendor releases a software patch. |
| The administrator or user naturally wants to apply the patch and then make sure existing VMs |
| start using it. Whether a software update is involved or not, it's also possible to simply |
| switch a VM from its current template to any other desired template.</para> |
| <para>To change a VM's base image, call the restoreVirtualMachine API command and pass in the |
| virtual machine ID and a new template ID. The template ID parameter may refer to either a |
| template or an ISO, depending on which type of base image the VM was already using (it must |
| match the previous type of image). When this call occurs, the VM's root disk is first destroyed, |
| then a new root disk is created from the source designated in the template ID parameter. The new |
| root disk is attached to the VM, and now the VM is based on the new template.</para> |
| <para>You can also omit the template ID parameter from the restoreVirtualMachine call. In this |
| case, the VM's root disk is destroyed and recreated, but from the same template or ISO that was |
| already in use by the VM.</para> |
| </section> |