Virtualization in Linux

Virtualization has transformed the way operating systems and applications run on hardware by enabling the creation of virtual instances of computers. For Linux users, the concept of virtualization harnesses the power of Linux's kernel features and tools, offering efficient resource utilization, ease of management, and increased flexibility. In this article, we will delve into the key concepts surrounding virtualization in Linux, particularly focusing on KVM (Kernel-based Virtual Machine) and how you can effectively set up and manage virtual machines.

Understanding Virtualization

At its core, virtualization is the process of creating virtual versions of physical resources. It allows a single physical machine to host multiple virtual machines (VMs), each with its own operating system and applications. This not only leads to improved hardware utilization but also provides an isolated environment for running applications without interfering with one another.

Types of Virtualization

Full Virtualization: This involves running a complete hardware emulation, enabling a VM to run any operating system. The guest OS is unaware that it is running on virtualized hardware. KVM is an example of this type.
Paravirtualization: Unlike full virtualization, the guest OS is modified to work in a virtualized environment. This leads to improved performance but requires OS modifications.
Container-based Virtualization: This approach, exemplified by tools like Docker, allows multiple isolated applications to run on the same OS kernel, sharing the host OS. While not a traditional form of virtualization, it provides an efficient way to run applications without needing full OS instances.

For this article, we will mainly focus on full virtualization through KVM.

What is KVM?

KVM (Kernel-based Virtual Machine) is a virtualization solution embedded within the Linux kernel. It allows the Linux kernel to function as a hypervisor, enabling it to run multiple isolated virtual environments (VMs) on a single physical machine. KVM is renowned for its performance, scalability, and strong security features, making it an ideal choice for both desktop and server environments.

Key Features of KVM

Integration with Linux: Since KVM utilizes the Linux kernel, it benefits from all the performance enhancements, security updates, and support available in the Linux ecosystem.
Support for Various Operating Systems: KVM can run many operating systems as guests, including various distributions of Linux, Windows, and even BSD Unix.
Performance: KVM takes advantage of hardware virtualization features available in modern CPUs, such as Intel VT-x and AMD-V, which allow for efficient execution of guest instructions.
Scalability: KVM can support numerous VMs on a single host machine, allowing enterprises to scale operations without needing additional physical servers.
Storage Options: KVM supports a wide range of storage formats, including qcow2 (QEMU Copy On Write), raw, and more, providing flexibility in how virtual disks are managed.

Setting Up KVM

Prerequisites

Before you can start creating virtual machines using KVM, ensure that your system meets the following prerequisites:

Hardware Support: Check that your CPU supports hardware virtualization. You can verify this by executing the following command:
```
egrep -c '(vmx|svm)' /proc/cpuinfo
```
If the output is greater than 0, your CPU has virtualization support.
Install KVM and Related Packages: You need to install KVM and a few other essential packages. On a Debian-based system like Ubuntu, you can run:
```
sudo apt update
sudo apt install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils
```
For Red Hat-based systems, use:
```
sudo yum install qemu-kvm libvirt libvirt-python libguestfs-tools
```
Start and Enable the Libvirt Service:
```
sudo systemctl enable --now libvirtd
```

Creating Your First Virtual Machine

Once you have KVM installed, you can create virtual machines either using graphical tools or command-line interfaces. Here, we will cover both approaches briefly.

Using Virt-Manager (GUI)

Virt-Manager is a graphical interface to manage your virtual machines.

Install Virt-Manager:
```
sudo apt install virt-manager
```
Launch Virt-Manager from your application menu.
Click on the "Create a new virtual machine" button.
Follow the wizard to specify the OS installation method, allocate resources (CPU, RAM), and set storage options for your VM.
Once configured, click "Finish" to start creating the VM.

Using Command Line

For those who prefer the command line, the virt-install tool can be very powerful:

sudo virt-install \
--name myvm \
--os-variant ubuntu20.04 \
--vcpus 2 \
--memory 2048 \
--disk path=/var/lib/libvirt/images/myvm.img,size=20 \
--cdrom /path/to/ubuntu.iso \
--graphics none \
--console pty,target_type=serial \
--network network=default

In this command:

Replace myvm with your desired virtual machine name.
Adjust memory, CPUs, and disk size according to your requirements.
Replace /path/to/ubuntu.iso with the actual path to the installation media.

Managing Virtual Machines

After setting up your VMs, it’s essential to learn how to manage them effectively. You can use virsh, the command-line tool for managing KVM:

List all VMs:
```
virsh list --all
```
Start a VM:
```
virsh start myvm
```
Shutdown a VM:
```
virsh shutdown myvm
```
Connect to a VM console:
```
virsh console myvm
```

Networking in KVM

Networking is a critical aspect to consider when working with virtualization. KVM can be configured to use various networking modes:

NAT (Network Address Translation): The VM shares the host's IP address, and internal packets are routed via the host. This setup is simple and ideal for isolated development environments.
Bridged Networking: VMs connect to the same physical network as the host. This allows VMs to be accessed from other machines on the network, making it suitable for server-type setups.
Host-only Networking: This mode allows VMs to communicate with each other and the host but not with external networks.

Configuring Bridge Networking

To set up bridged networking, you need to create a bridge interface on your host system. Here’s how you might do it on a typical Linux system using netplan:

Edit the netplan configuration file (usually found in /etc/netplan/):

network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: no
  bridges:
    br0:
      dhcp4: yes
      interfaces: [ens33]

Apply the changes:
```
sudo netplan apply
```

After making these changes, you can attach your VMs to the br0 bridge in their network settings.

Conclusion

Virtualization in Linux, particularly using KVM, provides a robust and efficient way to manage computing resources. It enhances flexibility, reduces costs, and allows users and businesses to harness the full potential of their hardware. With tools like Virt-Manager for a graphical interface and virsh for command-line control, managing virtual machines has never been easier.

Whether you want to run multiple OSs on a single piece of hardware for testing or develop isolated environments for different applications, mastering KVM will empower you in your virtualization journey. Dive in, explore the capabilities, and enjoy the versatility that virtualization in Linux offers!

Computer Science - Linux Operating System