As it may happen on any physical machine, some user operations as e.g. a major upgrade of the Operative System, or a modification of the partition layout or bootloader, may end up with a Compute instance not being able to boot normally anymore.

To that purpose, a rescue mode exists in order do get an access to the root disk of the machine by booting from a different source. The boot program used in this case is the open source project called Netboot and allows to start a variety of Linux, BSD, ISO images, specialized installers or utilities.

Pre-Requisites to Work With Rescue Mode

Rescue mode is not a default operation, and can be operated only via the CLI or API. It requires:

Moreover, if you wish to use a custom ISO the latter must be loaded in a publicly accessible URL. You can use e.g. our Object Storage service for this scope.

Warning

Exoscale is solely responsible for the instance to boot in rescue mode with the Netboot loader. Any operation performed in Netboot, and the repair of the instance itself is out of the Exoscale standard support scope. The examples provided in this page are solely intended to point the user in the right direction, with no guarantee on their outcome. A proper knowledge of tooling and operations is required.

Booting Into Rescue Mode

To reboot in rescue mode, first start by shutting down your instance. This can be performed via the CLI or via the portal in the instance details:

    exo vm stop broken-vm

You can then start your instance in either BIOS or UEFI rescue mode depending on the template you are using.

To start an instance in BIOS rescue mode:

    exo vm start --rescue-profile=netboot broken-vm

To start an instance in UEFI rescue mode:

    exo vm start --rescue-profile=netboot-efi broken-vm

Start instance rescue mode

The instance will now boot the Netboot image.

Accessing the Rescue Mode

To access the rescue mode, launch the Exoscale portal and navigate to the instance detail view. Once on the detailed view, click the OPEN CONSOLE button.

A new window will open and display the instance console and the Netboot menu:

Netboot rescue menu from console

You can now perform any operation you require to repair the instance and, once finished, reboot your instance normally. Once rebooted, the instance will exit rescue mode and try to boot from its root disk.

Booting From a Custom ISO Image in BIOS Rescue Mode

Through rescue mode, it is possible to boot an instance from an external ISO as long as the latter supports virtIO storage and network drivers. With this method a bare metal recovery is possible for example.

Note

The custom ISO must be located in a publicly accessible URL. You can use our Object Storage service for this scope.

To boot from an external ISO, perform the following steps:

  • Start your instance in rescue mode as described above
  • From the main Netboot menu select Tools -> Utilities
  • Then select netboot.xyz tools -> Test Distribution ISO
  • Enter the public URL of the target ISO (e.g. http://centos.anexia.at/centos/7.7.1908/isos/x86_64/CentOS-7-x86_64-LiveGNOME-1908.iso to boot a CentOS Live CD).

Netboot_rescue_menu_from_console_iso_image

Booting From a Windows Recovery Image

Would you need to recover a Windows instance from a Windows Recovery Image, you can leverage two ISOs we put at your disposal, where all the needed virtIO drivers have already been integrated:

  • http://sos-de-muc-1.exo.io/windows-recovery-image/w2k16 a Windows 2016 recovery image
  • http://sos-de-muc-1.exo.io/windows-recovery-image/w2k19 a Windows 2019 recovery image

Warning

Although provided for public use, the mentioned Windows Recovery Images are provided “as is”, without warranty of any kind. As for any other rescue mode operation, the user is solely responsible for the outcome of its actions, and the rescue operations beyond the booting of the Netboot loader are out of the Exoscale standard support scope.

Netboot_rescue_menu_from_console_iso_image

To proceed:

  • Start your instance in rescue mode as described above
  • From the main Netboot menu select Distributions -> Windows
  • Select Options -> Base URL
  • Enter the URL corresponding to your instance’s Windows version from the options listed above. You will be asked to enter any key to return to the Windows menu.
  • Once back in the Windows menu select Load Microsoft Windows Installer...
  • The Windows Recovery Image will load and you will be prompted to enter some basic options. Click Next when ready.
  • In the next screen click “Repair your computer” in the bottom left

You can now start to recover your Windows instance.