KVM on Ubuntu

KVM (Kernel-based Virtual Machine) is a virtualization technology built into the Linux kernel that allows Linux to run multiple virtual machines (VMs) on a single physical server. KVM converts the Linux kernel into a Type-1 (bare-metal) hypervisor using CPU virtualization features.

In this blog post, I describe what KVM is and how to enable KVM on Linux Server. 

Main Linux virtualization components:

• Linux kernel with KVM module
• Modules: kvm.ko, kvm-intel.ko or kvm-amd.ko
• Uses hardware virtualization (Intel VT-x / AMD-V)
• QEMU
• Provides hardware emulation.
• Runs the VM process in userspace.
• libvirt (optional but common)
• Management API and tools (virsh, virt-manager)
• Virtual devices
• Disk: virtio-blk
• Network: virtio-net
• GPU: virtio-gpu 

Why KVM is powerful

• Near bare-metal performance (hardware virtualization)
• Part of Linux kernel (no separate hypervisor OS needed)
• Open source
• Used by many clouds and platforms

Examples of platforms built on KVM

• OpenStack
• Apache CloudStack
• Proxmox VE
• oVirt / Red Hat Virtualization
• Google Compute Engine

Enable Linux Virtualization on Ubuntu Server

I have Ubuntu server in my home lab, so let's enable KVM on it.

Install KVM onto Ubuntu Server

KVM must be explicitly installed.  

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

Check if KVM works ...

kvm-ok

 root@acs-ubuntu-01:/home/dpasek# kvm-ok  
 INFO: /dev/kvm exists  
 KVM acceleration can be used  
 root@acs-ubuntu-01:/home/dpasek#   

Or other way to check kernel module ... 

lsmod | grep kvm 

 root@acs-ubuntu-01:/home/dpasek# lsmod | grep kvm   
 kvm_intel       487424 0  
 kvm            1409024 1 kvm_intel  
 irqbypass        12288 1 kvm  
 root@acs-ubuntu-01:/home/dpasek#  

Enable libvirt on Ubuntu Server

libvirt is a virtualization management API and toolkit used to control hypervisors such as KVM, QEMU, Xen, and others. libvirt provides a unified management layer for virtualization. Instead of controlling hypervisors directly, tools communicate with libvirt, which then controls the hypervisor (KVM).

Typical operations:

• create virtual machines
• start/stop VMs
• configure CPU, RAM, disks
• attach networks and storage
• migrate VMs between hosts
• monitor VM state 

Important libvirt components

libvirtd

The daemon running on the hypervisor host.

Responsible for:

• controlling hypervisors
• managing VM lifecycle
• exposing API (local or remote)

Service:

systemctl status libvirtd

virsh

CLI tool to manage VMs.

Examples:

List VMs

virsh list --all

Start VM

virsh start vm1

Shutdown VM

virsh shutdown vm1 

Networking with libvirt

libvirt can manage:

• Linux bridges
• NAT networks
• Open vSwitch
• SR-IOV interfaces

Storage management

libvirt also manages storage pools:

• directory
• LVM
• iSCSI
• NFS
• Ceph

Virtualization capabilities of the host system

Command ... 

virsh capabilities 

... displays the host’s virtualization features, supported guest types, CPU details, and hypervisor capabilities. The command prints a large XML document describing what the host can run.

Typical sections include:

• Host CPU information
• Supported virtualization types
• Supported machine types
• NUMA topology
• Supported guest architectures 

Conclusion

This one is just a short blog post how to enable KVM on Ubuntu server, but I also do test 

• Apache Cloud Stack as a Virtualization Management Platform of KVM hypervisors
• OVN - Open Virtual Networking which is leveraging Open vSwitch as a data plane

Hope you find this one useful.