KVM Installation

KVM Installation

KVM (Kernel-based Virtual Machine) is the Linux kernel's built-in hypervisor. It turns Linux into a Type-1 hypervisor, allowing you to run multiple isolated virtual machines on a single physical host. Combined with QEMU (which provides hardware emulation) and libvirt (a management API), KVM gives you full virtualization comparable to VMware ESXi or Hyper-V at zero licensing cost. Ubuntu uses this stack for its own cloud infrastructure.

What is KVM?

KVM virtualization stack:
  Physical Hardware (CPU with VT-x/AMD-V extensions)
       |
  Linux Kernel + KVM module (hardware virtualization support)
       |
  QEMU (hardware emulation: virtual disks, NICs, etc.)
       |
  libvirt (management API and daemon)
       |
  virsh (CLI) / virt-manager (GUI) / Cockpit (web UI)

Hardware requirements

# Verify CPU supports hardware virtualization:
grep -c -E "vmx|svm" /proc/cpuinfo    # > 0 means virtualization supported

# vmx = Intel VT-x
# svm = AMD-V

# Check if KVM module is loaded:
lsmod | grep kvm

Expected output on capable hardware

kvm_intel    331776  0      ← Intel VT-x (OR kvm_amd for AMD)
kvm          987136  1 kvm_intel

Installing KVM

sudo apt update
sudo apt install -y qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils virt-manager

# Add your user to the libvirt group (to manage VMs without sudo):
sudo usermod -aG libvirt $USER
sudo usermod -aG kvm $USER
newgrp libvirt    # Apply group change in current session

# Enable and start libvirtd:
sudo systemctl enable --now libvirtd

# Verify installation:
virsh list --all    # Should show empty list (no VMs yet)

Creating your first VM

# Create a VM using virt-install:
sudo virt-install   --name ubuntu-test   --ram 2048   --vcpus 2   --disk path=/var/lib/libvirt/images/ubuntu-test.qcow2,size=20   --os-variant ubuntu22.04   --network network=default   --graphics none   --console pty,target_type=serial   --location 'http://archive.ubuntu.com/ubuntu/dists/jammy/main/installer-amd64/'   --extra-args 'console=ttyS0,115200n8 serial'

# Or with an ISO file:
sudo virt-install   --name ubuntu-test   --ram 2048 --vcpus 2   --disk path=/var/lib/libvirt/images/ubuntu-test.qcow2,size=20   --cdrom /home/irfan/ubuntu-22.04-server.iso   --network network=default

Conclusion

After installing the KVM stack, run virsh list --all to verify libvirtd is working correctly. The default NAT network (network=default) provides outbound internet access for VMs without additional configuration. For VMs that need to be reachable from the local network, you need a bridged network (covered in the libvirt-basics article). KVM VMs live in /var/lib/libvirt/images/ as QCOW2 disk images.