KVM Virtualization | Install KVM | RHEL/CentOS 8

In this article I will share step by step tutorial to install KVM on RHEL 8 or CentOS 8 Linux. But before we start with the installation steps, let us understand little bit about KVM Virtualization and about KVM Hypervisor.

What is Virtualization?

• CentOS/RHEL 8 provides the virtualization functionality (so does many other distros..)
• This enables a machine running CentOS/RHEL 8 to host multiple virtual machines (VMs), also referred to as guests.
• VMs use the host’s physical hardware and computing resources to run a separate, virtualized operating system (guest OS) as a user-space process on the host’s operating system.

What is Hypervisor?

• The basis of creating virtual machines (VMs) in RHEL and CentOS 8 is the hypervisor.
• It is a software layer that controls hardware and enables running multiple operating systems on a host machine.
• The hypervisor in RHEL/CentOS includes the Kernel-based Virtual Machine (KVM) module and virtualization kernel drivers, such as virtio and vfio.
• These components ensure that the Linux kernel on the host machine provides resources for virtualization to user-space software.

There are two types of hypervisor

• Type 1 Hypervisor
• Type 2 Hypervisor

What is KVM?

• KVM is short abbreviation for Kernel Based Virtual Machine.
• It gives the Linux kernel hypervisor capabilities.
• Because KVM is implemented directly in the Linux kernel, it has great support across a wide variety of Linux distros.
• At the user-space level, the QEMU emulator simulates a complete virtualized hardware platform that the guest operating system can run in, and manages how resources are allocated on the host and presented to the guest.
• In addition, the libvirt software suite serves as a management and communication layer, making QEMU easier to interact with, enforcing security rules, and providing a number of additional tools for configuring and running VMs.

Pre-requisites to Install and Configure KVM

Install RHEL 8 or CentOS 8

Red Hat Enterprise Linux 8 or CentOS 8 must be installed on your physical host machine.

Verify support for KVM Virtualization

• The physical host machine must support KVM Virtualization.
• On an Intel platform, the flag that shows support for full hardware-based virtualization is the vmx flag.
• To check whether an Intel processor has support for vmx, you could grep for the desired flag in /proc/cpuinfo, like so

# lscpu | grep -i "Model Name"
Model name:            Intel(R) Xeon(R) CPU E5-2640 v3 @ 2.60GHz

# grep -i -o vmx /proc/cpuinfo | uniq
vmx

The presence of vmx in this sample output shows that necessary CPU extensions are in place on the Intel processor.

• On an AMD platform, the flag that shows support for full hardware-based virtualization is the Secure Virtual Machine (svm) flag.
• To check whether an AMD processor has support for svm, you could grep for the desired flag in /proc/cpuinfo, like so:

# lscpu | grep -i "Model Name"
Model name:            AMD EPYC 7402P 24-Core Processor

# grep -i -o svm /proc/cpuinfo | uniq
svm

The presence of svm in this sample output shows that necessary CPU extensions are in place on the AMD processor.

Register RHEL 8 to RHN (Optional)

• I have mentioned this chapter as Optional but it is recommended if you are using RHEL 8.
• On CentOS 8 you only need an active internet connection to connect to CentOS repositories
• On RHEL 8 you should register your host to RHN to get latest updates. We will need this in our next chapters to set up KVM HA Cluster
• To only install KVM you can just create an offline repository using Red Hat 8 ISO DVD to install KVM Virtualization related packages

My RHEL 8 node is registered with Red Hat Network

[root@rhel-8 ~]# subscription-manager list
+-------------------------------------------+
    Installed Product Status
+-------------------------------------------+
Product Name:   Red Hat Enterprise Linux for x86_64
Product ID:     479
Version:        8.2
Arch:           x86_64
Status:         Subscribed
Status Details:
Starts:         12/10/2019
Ends:           12/10/2020

Install KVM on RHEL/CentOS 8

To use virtualization in RHEL/CentOS 8, you must enable the virtualization module, install virtualization packages, and ensure your system is configured to host virtual machines (VMs).

I hope you are already aware of YUM alternative DNF tool

[root@rhel-8 ~]# dnf module install virt

Once installed you can check if kvm module is loaded on your Physical Host

[root@rhel-8 ~]# lsmod | grep kvm
kvm_intel             290816  16
kvm                   761856  1 kvm_intel
irqbypass              16384  2 kvm

On AMD host, you would get output like below

# lsmod | grep kvm
kvm_amd              2177260  0
kvm                   621480  1 kvm_amd
irqbypass              13503  1 kvm

Install the virt-install and virt-viewer packages. We will need them to create KVM Virtual Machines

[root@rhel-8 ~]# dnf install virt-install virt-viewer

Enable and start libvirtd service

Start and enable the libvirtd service

[root@rhel-8 ~]# systemctl enable libvirtd --now

Verify KVM Virtualization Status

After you install KVM rpms and start libvirtd service, verify if your RHEL/CentOS 8 physical host is enabled to support KVM Virtualization

[root@rhel-8 ~]# 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                         : PASS
  QEMU: Checking if IOMMU is enabled by kernel                               : WARN (IOMMU appears to be disabled in kernel. Add intel_iommu=on to kernel cmdline arguments)

Here our first part of KVM Tutorial is complete. Now our RHEL/CentOS 8 physical host is ready to create KVM Virtual Machines

Lastly I hope the steps from the article to install LVM on RHEL/CentOS 8 Linux was helpful. So, let me know your suggestions and feedback using the comment section.