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vKVM Rescue System

vKVM

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

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 the normal network connection works without problems).

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):

47772 SSH
47773 Web-Interface (SSL)
47774 VNC (SSL)

Starting the Rescue System

The Rescue System can be activated from Robot. After choosing the desired server from the server overview (Menu "Server" -> click on the desired server) go to the tab "Rescue" (here you'll need to select "vkvm" from the list of possible options). 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:

Refresh Refreshes the console
Send Ctrl-Alt-Del Sends Ctrl-Alt-Del (soft reset) to the virtual machine
Send HW Reset Performs a reset of the virtual machine

With its default settings, vKVM tries to boot from the first drive. 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 a Ctrl-Alt-Del.

Limitations

Due to the fact that with vKVM the server is started in a virtual machine, and thus doesn't have direct access to the physical hardware components of the actual server, it can lead to limitations for certain operating systems.

The following limitations are currently known:

Half RAM usage

Since the vKVM hypervisor itself needs memory, and it only runs in RAM, the virtual machine is started with only 50% of the actually available physical memory.

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.

VMware ESXi, Citrix XenServer, OpenSolaris

Are not supported.

RAID controllers

Configured units are passed through as SCSI devices to the VM. However it is not possible 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


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