Unlocking Virtualization: How to Run VirtualBox and KVM Together on Linux
For developers, system administrators, and tech enthusiasts using Linux, virtualization is an indispensable tool. Two of the most popular solutions are VirtualBox and KVM (Kernel-based Virtual Machine). VirtualBox is celebrated for its user-friendly interface and cross-platform compatibility, while KVM is revered for its high performance and deep integration with the Linux kernel. However, running both on the same machine often leads to a frustrating and common error: VirtualBox being unable to access hardware virtualization extensions.
This guide explains why this conflict occurs and provides a clear, actionable solution to allow these powerful tools to coexist on your system.
Understanding the Core Conflict: A Battle for Hardware Access
The root of the problem lies in how these hypervisors work. A hypervisor is the software that creates and runs virtual machines (VMs). To achieve near-native performance, modern hypervisors rely on special processor features known as hardware virtualization extensions—Intel VT-x for Intel processors and AMD-V for AMD processors.
The critical rule is that only one hypervisor can control these hardware extensions at a time.
- KVM is a Type-1 hypervisor. Its modules (
kvm_intelorkvm_amd) are loaded directly into the Linux kernel at boot. When active, KVM takes exclusive control of the VT-x or AMD-V features. - VirtualBox is a Type-2 hypervisor. It runs as an application on top of your existing operating system. When you try to start a 64-bit VM, VirtualBox also attempts to access those same hardware extensions.
If KVM’s modules are already loaded, VirtualBox finds the hardware “occupied” and is forced to fall back to a much slower software virtualization mode, or more commonly, it will fail to start a 64-bit guest OS with an error like “VT-x is not available (VERRVMXNO_VMX).”
The Solution: Manually Toggling Hypervisors
Since both can’t run simultaneously with hardware acceleration, the most effective solution is to simply unload the KVM modules when you want to use VirtualBox and reload them when you’re done. This is a safe and straightforward process.
Step 1: Check if KVM Modules Are Loaded
First, open your terminal and check if KVM is currently active. You can do this with a simple command that lists loaded kernel modules and filters for “kvm”:
lsmod | grep kvm
If you see output that includes kvm_intel or kvm_amd, the modules are active, and you will need to unload them to run VirtualBox with hardware acceleration.
Step 2: Unload the KVM Modules
To free up the hardware extensions for VirtualBox, you need to remove the KVM modules. Use the modprobe command with the -r flag for removal.
For an Intel-based system:
sudo modprobe -r kvm_intel
sudo modprobe -r kvm
For an AMD-based system:
sudo modprobe -r kvm_amd
sudo modprobe -r kvm
After running the appropriate commands, you can verify they are gone by running lsmod | grep kvm again. There should be no output. Now, you can launch VirtualBox and start your virtual machines with full hardware acceleration.
Step 3: Re-enabling KVM When You’re Finished
When you are done using VirtualBox and want to use KVM-based tools again (like QEMU/Libvirt), you can easily reload the modules.
For an Intel-based system:
sudo modprobe kvm_intel
For an AMD-based system:
sudo modprobe kvm_amd
This simple toggle allows you to switch between hypervisors based on your needs, ensuring you always have access to the best performance for the task at hand.
Final Thoughts: Managing Your Virtualization Workflow
While it might seem inconvenient, this conflict is a fundamental aspect of how hypervisors interact with hardware. By understanding that only one can have privileged access at a time, the solution becomes clear. Toggling the KVM kernel modules is the most reliable and performant method for using both VirtualBox and KVM on the same Linux machine.
By mastering this simple command-line process, you gain the flexibility to leverage the unique strengths of both virtualization platforms without compromise, ensuring your workflow remains efficient and powerful.
Source: https://kifarunix.com/use-virtualbox-vms-on-kvm/
