Nested virtualization problems: KVM, Hyper-V, WSL 2 and emulators

Nested virtualization gives your server the processor features hypervisors need. When something still refuses to start, the message usually names the missing piece. Start with Step 1, which rules out the most common cause in a minute.

Step 1: Check the server type and the extensions

Nested virtualization is part of VDS plans and nested dedicated servers. VPS plans do not offer it, so hypervisors, WSL 2, Docker Desktop and Android emulators that need hardware acceleration cannot run on them.

grep -Ec '(vmx|svm)' /proc/cpuinfo
ls -l /dev/kvm
lsmod | grep kvm

Get-ComputerInfo -Property HyperV*
systeminfo | findstr /i "Hyper-V"

If the extensions are missing on a VDS, restart the server once. If they are still missing, open a ticket with this output.

Linux: /dev/kvm is missing or not accessible

kvm-ok prints KVM acceleration can NOT be used. With a count of 0 above, the extensions are not visible (see Step 1). With a count above 0, load the module for your processor:

sudo modprobe kvm_intel
sudo modprobe kvm_amd

Only one of the two loads, depending on the processor. Check ls -l /dev/kvm afterwards.

Could not access KVM kernel module: Permission denied. Your user may not use /dev/kvm. Add it to the group that owns the device (usually kvm) and log in again:

sudo usermod -aG kvm $USER

Windows: Hyper-V will not install

Server Manager or Install-WindowsFeature reports that the processor does not have the required virtualization capabilities. Hyper-V cannot see the extensions. Check Step 1 and open a ticket if the server is a VDS.

Hyper-V is installed, but VMs do not start: "The virtual machine could not be started because the hypervisor is not running". The hypervisor is not set to start with Windows. Check and fix the boot setting in an elevated prompt, then restart:

bcdedit /enum | findstr -i hypervisorlaunchtype
bcdedit /set hypervisorlaunchtype Auto

Windows: WSL 2 error 0x80370102

Error: 0x80370102 The virtual machine could not be started because a required feature is not installed. Microsoft's fix list for this error applies to servers too:

1. Make sure the server is a VDS and the extensions are visible (Step 1).
2. Make sure the Virtual Machine Platform component is installed, then restart.
3. Check hypervisorlaunchtype as shown above and set it to Auto.
4. Update or turn off third-party hypervisors such as older VMware or VirtualBox versions.

Hypervisor conflicts on Windows

Hyper-V, WSL 2 and some emulators use the Windows hypervisor. Older versions of other hypervisors cannot run while it is active, and some Android emulators ship separate builds for systems with Hyper-V. Either keep everything on the Windows hypervisor (current VMware and VirtualBox versions support running alongside Hyper-V) or turn Hyper-V-based features off and restart.

Docker Desktop on Windows Server

Docker Desktop is not supported on server versions of Windows. On a Windows Server VDS, run Docker Engine inside WSL 2 (WSL 2 on Windows Server); on a Windows desktop image, Docker Desktop uses WSL 2 or Hyper-V as usual.

Android emulators report that virtualization is off

Android emulators need hardware acceleration. On a VPS they cannot get it. On a VDS or nested dedicated server, check Step 1 and the emulator's own requirements; see Android emulator troubleshooting.

Nested guests are slow

• Give guests fixed memory and no more vCPUs than they need; never more than the VDS has.
• Use paravirtual devices: virtio disks and network cards in KVM and Proxmox VE, Generation 2 VMs in Hyper-V.
• Keep disk-heavy work such as databases on the VDS itself, not inside nested guests.
• Production workloads that need the whole machine belong on a dedicated server.

Next steps

• Back to the overview: VDS and nested virtualization.
• Build guests: KVM with libvirt or Hyper-V on a Windows VDS.