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What is the vKVM Rescue System?

The vKVM Rescue System allows you to start the operation system installed on the server in a virtual machine. With the help of vKVM, you can diagnose boot problems or adjust firewall settings, things that would normally require a LARA remote console.

The virtualization technology used is KVM. SATA and IDE drives are passed through to the guest system. Network access is also directly possible (the virtual machine uses the same MAC address as the physical NIC, which means that DHCP and the Rescue System also work without problems inside the vKVM.)

The following ports cannot be used by the guest system in vKVM mode (i.e. incoming packets to these ports are not forwarded to the guest):

How do I start the Rescue System?

Before you can use the vKVM Rescue System, you have to activate it in your Robot account (https://robot.your-server.de/) in the Rescue tab of the Server menu. After activation a URL and a user name/password are shown. Open the URL in a web browser to get to the vKVM web site. The application requires Java.

In addition to viewing the console output and forwarding keyboard and mouse input, the vKVM interface offers the following additional functions:

With its default settings, vKVM tries to boot from PXE. This allows you to boot the Linux Rescue System in vKVM. To boot from the drive instead, press "Q" when asked if you want to boot from PXE:

Boot from (N)etwork or (Q)uit?

To leave vKVM mode and directly boot from the drive again, shut down the virtual machine using "Send Ctrl-Alt-Del" (to prevent corruption of the file system). Then reboot the real server using the Hetzner Robot by also sending Ctrl-Alt-Del.

Limitations

Because vKVM starts the operating system in a virtual machine, other (virtual) hardware components are used instead of the actual hardware of the real server. For some operating system this can lead to limitations in the use of vKVM.

The following limitations are currently known:

Linux

Because the SATA drives are detected as SCSI devices in vKVM, the kernel in use must provide the right modules for the SCSI controller (LSI Logic / Symbios 53c895a).

If the normal distribution kernel is being used, it (almost) always has the correct modules. However, self-compiled kernels may not have this module, depending on their configuration.

Windows

vKVM automatically detects Windows installations and forwards the SATA drives as IDE drives, as the SCSI controller cannot be used by Windows without problems.

Windows deactivates the IDE drivers if no IDE drives are detected during installation. They must be reactivated before using vKVM using the following guide: Microsoft Support site

The main problem for Windows is that the emulated hardware greatly differs from the physical hardware. Depending on the license model, this may or may not require a reactivation of your Windows license.

It is also not possible to change the network settings of the physical NIC as the corresponding network interface is not displayed in the control panel.

OpenSolaris, ESXi, Citrix XenServer

Currently not supported.

3ware-Controller

Already configured units are passed through as SCSI devices to the VM. However it is not possible to use the 3ware client "tw_cli" to access the controller. Please use the regular Hetzner Rescue System for this purpose.

Network

Servers with more then one network card will only have one card passed through to the VM. Packets received on any other physical NIC are forwarded to the first NIC in the virtual machine. Outgoing packets are always sent out of the first physical NIC.

Intel VT or AMD-V

The virtualization features of certain CPUs are not passed through to the virtual machine. Servers with CPUs that do not support Intel VT or AMD-V will only run very slow in vKVM mode.

32-bit CPUs

32-bit CPUs are not supported.

Black screen

On Ubuntu 10.04 (and probably higher), the vga16fb module needs to be disabled in order to use vKVM. Otherwise, you only see a black screen after booting.

To disable this module edit the file /etc/modprobe.d/blacklist-framebuffer.conf and add this line:

blacklist vga16fb