Virtualization New Added 26 October 2026

Proxmox: TASK ERROR: KVM virtualisation configured, but not available

The VM is set to use hardware acceleration (kvm: 1, the default) but the host has no /dev/kvm. On bare metal that means Intel VT-x or AMD-V is switched off in the firmware settings. When Proxmox is itself running as a VM, say a home lab under VMware, Hyper-V or another Proxmox, the outer hypervisor must pass nested virtualisation through, and none of them does that by default. Turning KVM off in the VM options lets it boot, but under pure emulation it is many times slower.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

# On the Proxmox host: does the CPU expose the extensions? 0 means no
grep -Ec '(vmx|svm)' /proc/cpuinfo
ls -l /dev/kvm
lsmod | grep kvm

# Bare metal: enable Intel VT-x or AMD SVM in the BIOS/UEFI, then reboot

# Proxmox running inside another hypervisor: enable nesting on the OUTER host
#   Proxmox:  qm set <vmid> --cpu host  (and check nested is Y below)
#             cat /sys/module/kvm_intel/parameters/nested
#   Hyper-V:  Set-VMProcessor -VMName pve -ExposeVirtualizationExtensions $true
#   VMware:   VM settings > CPU > Expose hardware assisted virtualization

# Last resort, and slow: run this one VM without KVM
qm set 100 --kvm 0

How to diagnose Virtualization errors

Virtualisation errors are usually about hardware virtualisation access: either it is disabled in firmware, or another hypervisor already holds it. On Windows, Hyper-V, WSL 2, Docker Desktop, Credential Guard and memory integrity all claim the virtualisation extensions, and VirtualBox or VMware then fails with a message that mentions VT-x but not the actual conflict.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Confirm virtualisation is enabled at the CPU level: grep -E 'vmx|svm' /proc/cpuinfo on Linux, or the Performance tab of Task Manager on Windows.
On Windows, check what else is using the hypervisor: bcdedit /enum | findstr hypervisorlaunchtype and whether Hyper-V, WSL 2 or Core Isolation are enabled.
On Linux, check /dev/kvm exists and that your user is in the kvm group; nested virtualisation must be enabled explicitly on cloud VMs.
Match guest additions and tools versions to the hypervisor version: mismatches cause shared folders, clipboard and display problems that look like guest OS bugs.
For WSL, run wsl --status and wsl --update; most WSL 2 errors are a stale kernel or a disabled Virtual Machine Platform feature.

Tools worth reaching for

grep -E 'vmx|svm' /proc/cpuinfo
wsl --status
bcdedit /enum
ls -l /dev/kvm
systemctl status libvirtd

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

pve.proxmox.com pve.proxmox.com

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