How to Install KVM on CentOS 8 Linux

Updated on March 4, 2022

This tutorial is a step-by-step guide to install KVM on CentOS 8 / CentOS 7 Linux. KVM (Kernel-based Virtual Machine) is a virtualization solution, that helps to turn your server into a hypervisor and run multiple virtual machines. This tutorial also explains how to set up and manage a virtualized environment with KVM in CentOS 8 or CentOS 7.

Pre-requisites

System running CentOS 8 / CentOS 7
Sudo privileges or root account
Access to the Command Line
Virtualization Technology (VT) enabled in your server’s BIOS

Install KVM on CentOS 8

Step 1: Verify support for hardware virtualization

Make sure that your server supports hardware virtualization by running the following command:

For Intel-based systems
# lscpu | grep Virtualization
Virtualization: VT-x
For AMD-based systems
# lscpu | grep Virtualization
Virtualization:      AMD-V

Also, make sure that KVM modules are loaded in the kernel

# lsmod |grep kvm
kvm_amd               135168  0
kvm                   880640  1 kvm_amd
irqbypass              16384  1 kvm

KVM Processor Support

KVM supports processors from Intel, AMD, ARMv7-A and later, PowerPC and S390 64 bit

Step 2: Update the system

# yum update

Step 3: Install all the virtualization packages

# yum install @virt

Step 4: Install tools to provision and manage Virtual Machines

# yum install virt-install virt-manager virt-viewer virt-top libguestfs-tools

Step 5: Verify Server Virtualization Setup

# virt-host-validate
  QEMU: Checking for hardware virtualization                                 : PASS
  QEMU: Checking if device /dev/kvm exists                                   : PASS
  QEMU: Checking if device /dev/kvm is accessible                            : PASS
  QEMU: Checking if device /dev/vhost-net exists                             : PASS
  QEMU: Checking if device /dev/net/tun exists                               : PASS
  QEMU: Checking for cgroup 'cpu' controller support                         : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support                     : PASS
  QEMU: Checking for cgroup 'cpuset' controller support                      : PASS
  QEMU: Checking for cgroup 'memory' controller support                      : PASS
  QEMU: Checking for cgroup 'devices' controller support                     : PASS
  QEMU: Checking for cgroup 'blkio' controller support                       : PASS
  QEMU: Checking for device assignment IOMMU support                         : WARN (No ACPI IVRS table found, IOMMU either disabled in BIOS or not supported by this hardware platform)
  QEMU: Checking for secure guest support                                    : WARN (Unknown if this platform has Secure Guest support)

Step 6: Start libvirtd daemon and enable on boot

# systemctl start libvirtd
# systemctl enable --now libvirtd

Verify default bridged networking

Step 7: Verify the default network bridge configured

By default, libvirtd creates virbr0 as the bridged network.

# virsh net-info default
Name:           default
UUID:           81a01b0f-0275-4590-9e5b-e70e06668734
Active:         yes
Persistent:     yes
Autostart:      yes
Bridge:         virbr0

# nmcli device
DEVICE      TYPE      STATE                   CONNECTION
enp4s0f0    ethernet  connected               enp4s0f0
virbr0      bridge    connected (externally)  virbr0
enp4s0f1    ethernet  disconnected            --
enp4s0f2    ethernet  disconnected            --
enp4s0f3    ethernet  disconnected            --
lo          loopback  unmanaged               --
virbr0-nic  tun       unmanaged 

# nmcli connection show
NAME      UUID                                  TYPE      DEVICE
enp4s0f0  410ec4d8-46b4-4799-8a20-500932714366  ethernet  enp4s0f0
virbr0    d7ac2f70-b543-4e18-80b1-d89bd7606e11  bridge    virbr0
enp4s0f1  3a50fb83-0d98-43c3-848b-8fdcad24f495  ethernet  --
enp4s0f2  f2ba191a-b209-4a63-b2db-3607284344cb  ethernet  --
enp4s0f3  4c464e5f-2636-42f1-95bd-0b89b5858084  ethernet  --

For allocating IPs to VMs, libvirtd uses a lightweight DHCP and caching DNS server named DNSMAQ. You can see the config file with IP ranges.

# cat /var/lib/libvirt/dnsmasq/default.conf
##WARNING:  THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
##OVERWRITTEN AND LOST.  Changes to this configuration should be made using:
##    virsh net-edit default
## or other application using the libvirt API.
##
## dnsmasq conf file created by libvirt
strict-order
pid-file=/run/libvirt/network/default.pid
except-interface=lo
bind-dynamic
interface=virbr0
dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0
dhcp-no-override
dhcp-authoritative
dhcp-lease-max=253
dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile
addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts

# egrep '^(dhcp-range|interface)' /var/lib/libvirt/dnsmasq/default.conf
interface=virbr0
dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0

Configure bridged Networking

Step 8: Create a bridged interface

If you want your VMs reachable by other machines from your LAN, set up a network bridge on the server that is connected to your LAN. Otherwise, you can continue with further steps.

Create Virtual Machine on KVM

Step 9: Download bootable CentOS ISO file.

# wget http://centos.mirror.snu.edu.in/centos/7.9.2009/isos/x86_64/CentOS-7-x86_64-Minimal-2009.iso
# mv CentOS-7-x86_64-Minimal-2009.iso /var/lib/libvirt/boot/

CentOS 7 Minimal ISO file

I have downloaded CentOS 7 minimal installation ISO file.

Step 10: Create a virtual machine

Using command-line tool `virt-install`

# virt-install --name=CentOS7 --file=/var/lib/libvirt/images/centos7.qcow2 --file-size=15 --nonsparse --graphics=spice --ram=2048 --vcpus=2 --cdrom=/var/lib/libvirt/boot/CentOS-7-x86_64-Minimal-2009.iso --network bridge=virbr0 --os-type=linux --os-variant=generic

Starting install...
Allocating 'centos7.qcow2'                                                 |  15 GB  00:00:00

MobaXterm for exporting Display

I am using MobaXterm for exporting X-DISPLAY from the server on to my Windows machine.

Once the above command starts, virt-viewer shall open on your display as below: