How to Install KVM on Ubuntu

Introduction to KVM

KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V). It consists of a loadable kernel module that provides the core virtualization infrastructure and a processor-specific module.

Using KVM, you can run multiple virtual machines running unmodified Linux or Windows images. Each virtual machine has private virtualized hardware: a network card, disk, graphics adapter, etc. KVM is open-source software and has been part of the Linux kernel since version 2.6.20, making it a mature and reliable virtualization platform.

Prerequisites

Before proceeding with the KVM installation, ensure you have:

• Ubuntu Server or Desktop: This guide is tested on Ubuntu 20.04 LTS and Ubuntu 22.04 LTS
• CPU with Virtualization Support: Intel VT-x or AMD-V enabled in BIOS
• Sufficient RAM: At least 4GB, but 8GB or more recommended for running multiple VMs
• Disk Space: At least 20GB free space, more depending on your VM requirements
• Root or Sudo Access: Administrative privileges to install packages

Step 1: Check CPU Virtualization Support

The first step is to verify that your CPU supports hardware virtualization and that it's enabled in your BIOS. Run the following command to check:

egrep -c '(vmx|svm)' /proc/cpuinfo

If the output is 0, your processor doesn't support hardware virtualization, or it's disabled in the BIOS. If it's 1 or higher, your CPU supports virtualization.

For a more detailed check, use:

lscpu | grep Virtualization

You should see output similar to:

Virtualization:                  VT-x

Or for AMD processors:

Virtualization:                  AMD-V

If virtualization is not enabled, you'll need to reboot your system and enable Intel VT-x or AMD-V in your BIOS/UEFI settings. The exact steps vary by motherboard manufacturer, so consult your hardware documentation.

Step 2: Install KVM and Related Packages

Now that we've confirmed virtualization support, let's install KVM and its dependencies. First, update your package list:

sudo apt update

Install KVM and associated tools:

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

Let's break down what each package does:

• qemu-kvm: The main KVM hypervisor package providing QEMU with KVM support
• libvirt-daemon-system: Provides the libvirtd daemon for managing virtualization
• libvirt-clients: Command-line tools for managing VMs (virsh, virt-install, etc.)
• bridge-utils: Tools for network bridge configuration
• virtinst: Tools for creating virtual machines
• virt-manager: Graphical interface for managing VMs (optional for servers)

Step 3: Verify KVM Installation

After installation, verify that the KVM modules are loaded:

lsmod | grep kvm

You should see output similar to:

kvm_intel             282624  0
kvm                   663552  1 kvm_intel

Or for AMD processors:

kvm_amd               106496  0
kvm                   663552  1 kvm_amd

Check the status of the libvirtd service:

sudo systemctl status libvirtd

The service should be active and running. If it's not, start and enable it:

sudo systemctl start libvirtd
sudo systemctl enable libvirtd

Step 4: Add Your User to Required Groups

To manage VMs without sudo privileges, add your user to the libvirt and kvm groups:

sudo usermod -aG libvirt $USER
sudo usermod -aG kvm $USER

Log out and log back in for the group changes to take effect. You can verify your group membership with:

groups

You should see libvirt and kvm in the output.

Step 5: Configure Network Bridge (Optional)

By default, KVM creates a NAT-based network for VMs. If you want your VMs to appear as independent hosts on your network with their own IP addresses, you'll need to configure a network bridge.

First, install the network bridge utilities if not already installed:

sudo apt install bridge-utils

Edit the network configuration. For Ubuntu 20.04+ using Netplan, edit /etc/netplan/01-netcfg.yaml:

sudo nano /etc/netplan/01-netcfg.yaml

Add or modify the configuration to create a bridge:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      dhcp4: no
  bridges:
    br0:
      interfaces: [enp0s3]
      dhcp4: yes

Apply the network configuration:

sudo netplan apply

Verify the bridge was created:

ip addr show br0

Step 6: Create Your First Virtual Machine

Now that KVM is installed and configured, let's create your first virtual machine. We'll use Ubuntu Server as an example.

Download an ISO Image

First, download an operating system ISO. Let's use Ubuntu Server:

cd /var/lib/libvirt/images/
sudo wget https://releases.ubuntu.com/22.04/ubuntu-22.04.3-live-server-amd64.iso

Create VM Using virt-install

Create a new VM with the following command:

sudo virt-install \
  --name=ubuntu-vm \
  --vcpus=2 \
  --memory=2048 \
  --cdrom=/var/lib/libvirt/images/ubuntu-22.04.3-live-server-amd64.iso \
  --disk size=20 \
  --os-variant=ubuntu22.04

Let's break down the parameters:

• --name: Name of the virtual machine
• --vcpus: Number of virtual CPUs (2 in this example)
• --memory: RAM in MB (2048 = 2GB)
• --cdrom: Path to the ISO file
• --disk size: Disk size in GB
• --os-variant: Operating system type (improves performance)

This command will create the VM and automatically launch the console. Follow the on-screen prompts to install the operating system.

Step 7: Managing Virtual Machines with virsh

The virsh command-line tool is the primary way to manage VMs. Here are the most common commands:

List All VMs

virsh list --all

Start a VM

virsh start ubuntu-vm

Shutdown a VM

virsh shutdown ubuntu-vm

Force Stop a VM

virsh destroy ubuntu-vm

Auto-start VM on Boot

virsh autostart ubuntu-vm

Connect to VM Console

virsh console ubuntu-vm

To exit the console, press Ctrl + ]

View VM Information

virsh dominfo ubuntu-vm

Delete a VM

First, ensure the VM is stopped, then undefine it:

virsh shutdown ubuntu-vm
virsh undefine ubuntu-vm --remove-all-storage

Step 8: Using virt-manager (GUI)

If you installed virt-manager and have a desktop environment, you can manage VMs through a graphical interface.

Launch virt-manager from your applications menu or run:

virt-manager

The interface allows you to create, configure, and manage VMs visually. You can view console output, manage virtual hardware, create snapshots, and more.

Step 9: Performance Optimization

To get the best performance from your KVM virtual machines, consider these optimizations:

Enable Nested Virtualization (Optional)

If you need to run VMs inside VMs, enable nested virtualization:

For Intel processors:

echo "options kvm-intel nested=1" | sudo tee /etc/modprobe.d/kvm-intel.conf

For AMD processors:

echo "options kvm-amd nested=1" | sudo tee /etc/modprobe.d/kvm-amd.conf

Reload the KVM module:

sudo modprobe -r kvm_intel
sudo modprobe kvm_intel

Use VirtIO Drivers

VirtIO drivers provide better I/O performance for network and storage devices. When creating VMs, specify the VirtIO driver for disks and network interfaces:

--disk bus=virtio
--network bridge=br0,model=virtio

Allocate CPU Properly

Don't over-commit CPUs. As a general rule, don't allocate more vCPUs to VMs than you have physical cores. Leave at least 1-2 cores for the host system.

Common Issues and Troubleshooting

Issue: "KVM module is not loaded"

Solution: Ensure virtualization is enabled in BIOS and load the KVM module:

sudo modprobe kvm
sudo modprobe kvm_intel  # or kvm_amd

Issue: "Permission denied" when running virsh commands

Solution: Make sure your user is in the libvirt group and you've logged out/in:

sudo usermod -aG libvirt $USER

Issue: Poor VM performance

Solutions:

• Use VirtIO drivers for better I/O performance
• Allocate appropriate resources (don't over-commit)
• Ensure CPU virtualization extensions are enabled
• Use raw disk images instead of qcow2 for better performance (at the cost of features)

Issue: Network connectivity problems in VMs

Solution: Check the default network is active:

virsh net-list --all
virsh net-start default
virsh net-autostart default

Security Best Practices

When running KVM in a production environment, follow these security guidelines:

• Limit User Access: Only add trusted users to the libvirt group
• Isolate VMs: Use separate networks for different VM purposes
• Regular Updates: Keep both host and guest systems updated
• Enable Firewalls: Configure firewalls on both host and guests
• Use Snapshots: Take regular snapshots before major changes
• Secure Console Access: Use VNC with strong passwords or SSH tunnels
• Monitor Resources: Set up monitoring to detect unusual activity

Next Steps

Now that you have KVM installed and running, here are some things to explore:

• Learn about VM snapshots for backup and recovery
• Explore storage pools for better disk management
• Set up VM templates for quick deployment
• Configure virtual networks with VLANs and advanced routing
• Automate VM provisioning with tools like Terraform or Ansible
• Learn about live migration for moving VMs between hosts

Conclusion

KVM is a powerful virtualization platform that's free, open-source, and built into the Linux kernel. With this guide, you've learned how to install KVM on Ubuntu, verify CPU virtualization support, create and manage virtual machines using both command-line and graphical tools, and optimize performance.

Virtualization opens up many possibilities, from testing software in isolated environments to running production workloads efficiently. Take time to explore KVM's advanced features and integrate them into your workflow.