How To Install KVM on CentOS 8 / RHEL 8

KVM (
Kernel-Based Virtual Machine) is a virtualization software that provides an ability to run multiple virtual machines (guests) with the help of hardware virtualization extensions. It supports a wide variety of guest operating systems such as Linux, Windows, Solaris, and much more.

Virtual machines can be created or managed using command-line tools ( virsh, virt-install, and guestfish) or available graphical tools (
Cockpit web console).

Here, we will see how to install KVM on CentOS 8 / RHEL 8 and learn how to create virtual machines.

Prerequisites

Contents

1 Prerequisites
- 1.1 Check VT Support
- 1.2 Network Bridge
2 Install KVM
3 Create and Manage Virtual Machines
- 3.1 Command Line Mode
- 3.2 Graphical Mode
4 Conclusion

Check VT Support

As said earlier, You can run virtual machines only if the CPU has the support of hardware virtualization, either Intel VT or AMD-V.

To find whether your CPU supports VT features, run the following command.

egrep '(vmx|svm)' /proc/cpuinfo | wc -l

If the above command returns other than zero, then your hardware has VT enabled else it doesn’t.

Network Bridge

Create a network bridge on your system to let virtual machines can communicate with the external networks.

Here, we will create a virtual bridge called br0. To do that, first, create a bridge network configuration file.

vi /etc/sysconfig/network-scripts/ifcfg-br0

Update the configuration file with IP address and other network information. This bridge will be my primary network connection.

DEVICE="br0"
BOOTPROTO="static"
IPADDR="192.168.0.10"
NETMASK="255.255.255.0"
GATEWAY="192.168.0.1"
DNS1="192.168.0.1"
ONBOOT="yes"
TYPE="Bridge"

Edit your network interface’s configuration file to use the bridge br0.

vi /etc/sysconfig/network-scripts/ifcfg-ens33

Update the configuration with the below information.

DEVICE="ens33"
TYPE="Ethernet"
BOOTPROTO="none"
ONBOOT="yes"
BRIDGE="br0"

Reload the connection profile and restart the NetworkManager.

nmcli connection reload systemctl restart NetworkManager

Validate the network configuration using the ifconfig command.

ifconfig

Output:

Install KVM

Install the virtualization module. This module will install all the necessary packages for the system to support virtualization.

dnf module install -y virt

Install the virt-install and virt-viewer packages.

 dnf install -y virt-install virt-viewer

virt-install – Command-line tool to create virtual machines.

virt-viewer – Graphical console

Run the below command to validate if the host is ready to run virtual machines.

virt-host-validate

 Output: 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)

If you get QEMU: Checking for hardware virtualization: FAIL (Only emulated CPUs are available, performance will be significantly limited), then your machine can not run virtual machines.

Create and Manage Virtual Machines

If the host validation is good, then we can go and create virtual machines using either command-line or graphical interface.

Command Line Mode

The virt-install command is used to create virtual machines. The command needs few mandatory arguments to create a virtual machine such as VM name, CPU, memory, disk, network, installation media location, OS variant, and more.

virt-install --name=itzgeekguest --ram=1024 --vcpus=1 --os-type=linux --os-variant=rhel6.0 --cdrom=/tmp/CentOS-6.10-x86_64-minimal.iso --network bridge=br0 --graphics vnc,port=5901,listen=0.0.0.0 --disk path=/var/lib/libvirt/images/itzgeekguest.qcow2,size=10

Arguments	Purpose
–name	Name of the Virtual machine
–ram	Memory size in MB
–vcpus	Virtual CPU’s in numbers
–os-type	OS types like Linux, Windows, etc.
–os-variant	OS variant like RHEL 6, Solaris
–cdrom	Location of the ISO image
–network	Networking with Options
–graphics	Guest Console (VNC with port number)
–disk-path	Location of the disk (qcow2) with a size

Once you have run the above command, it will create a virtual machine and starts the VNC viewer session for the graphical console.

The virt-install command will not exit unless the os installation completes. So, open a new terminal and continue.

Allow the VNC connections in the firewall.

firewall-cmd --permanent --add-port=5901/tcp firewall-cmd --reload

Open a VNC viewer and access the VM console.

Few important commands to manage virtual machines.

List all virtual machines:

virsh list --all

Start a virtual machine:

virsh shutdown <vmname>

Gracefully shutdown a virtual machine:

virsh shutdown <vmname>

Restart a virtual machine:

virsh reset <vmname>

Force stop a virtual machine:

virsh destroy <vmname>

Delete a virtual machine along with its storage volumes:

virsh undefine <vmname> --remove-all-storage

Graphical Mode

CentOS 8 / RHEL 8 comes with Cockpit, a web-based interface for managing local and remote Linux systems.

READ: How To Install Cockpit on CentOS 8 / RHEL 8

The Cockpit provides additional add-ons to manage virtual machines from its console.

dnf install -y cockpit-machines

After the installation, restart the Cockpit service.

systemctl restart cockpit.socket

Access the Cockpit and go to the Virtual Machines page. You should see all your existing virtual machines.

If you don’t have any virtual machines, go ahead and create a new VM by clicking on Create VM. Fillup the Create New Virtual Machine form and click on Create.