KVM

Kernel-based Virtual Machine

Kernel-based Virtual Machine (KVM) is a core virtualization technology built into the Linux kernel. Think of virtualization as the ability of one computer (the "host") to pretend to be multiple separate computers, each running its own independent virtual machine (a "guest").

The key thing about KVM is that it turns your standard Linux kernel into a hypervisor. A hypervisor is the special layer of software that manages these virtual machines. Because KVM is part of the Linux kernel itself, it's very integrated into how Linux works. It uses special features built into modern CPUs (like Intel VT-x or AMD-V) to run the guest OS's instructions directly on the hardware, which makes it very fast and efficient.

Essentially, KVM lets a Linux host machine run multiple isolated guest machines, each behaving like a completely separate computer with its own OS (which can be Linux, Windows, or others) and its own allocated resources like CPU time, RAM (memory), and storage.

How it Works (Simply)

Imagine your Linux kernel is the main operating system running on your physical server. When you enable KVM, the Linux kernel gains the ability to act as a manager for other operating systems.

1. **The Kernel's New Role:** The Linux kernel uses the hardware virtualization extensions in the CPU to efficiently manage the guest virtual machine's demands. Instead of having to simulate everything the guest OS does in software, the Linux kernel can let the guest OS talk directly to the CPU for many tasks. 2. **Guest OS) Runs Natively:** The guest OS running inside the VM thinks it's running on real hardware. KVM helps it do this efficiently by using the CPU's hardware support. 3. **Help from User-Space:** While KVM provides the core virtualization capability, user-space tools (like QEMU) work alongside it. QEMU, for instance, helps emulate the virtual hardware devices that the guest OS needs, such as virtual network cards, virtual disk controllers, and virtual graphics cards. It also helps with managing the VM (starting, stopping, configuring).

So, KVM provides the speed and core ability to run guest OSs by using the Linux kernel and hardware features, while tools like QEMU handle the virtual devices and overall management.

Why Use KVM? (Benefits for a New User)

Even if you're not setting up virtualization yourself, you might benefit from it because many hosting providers use KVM. Here's why it's popular:

• **Good Performance:** Because KVM uses the CPU's own hardware virtualization extensions, virtual machines running on it are generally very fast, often performing close to a physical machine.
• **Stability and Reliability:** Being part of the well-tested Linux kernel, KVM is known for being stable and reliable.
• **Strong Isolation:** Each VM is isolated from the others on the same host. If something goes wrong in one VM, it typically doesn't affect the others or the host Linux system.
• **Flexibility:** KVM can run a wide variety of guest OSs, including different Linux distributions, Windows, and other operating systems.
• **Open Source:** KVM is free and open-source software, which often contributes to its widespread adoption and continuous improvement by a large community.

Common Use Cases

KVM is used in many scenarios:

• **Running Different Operating Systems:** You can use KVM on your Linux desktop to run another OS (like a specific Linux distribution or Windows) in a window, without needing to install it directly on your hardware.
• **Creating VPSs:** Many hosting providers use KVM to create and manage the isolated virtual private servers they sell. Each VPS is a VM running on a powerful physical server managed by the provider.
• **Cloud Computing:** Large cloud platforms often use KVM as the underlying technology to power the virtual servers they offer.
• **Consolidating Servers:** Businesses use KVM to run multiple server OSs (like a web server, database server, and mail server) as separate VMs on a single physical machine, which saves hardware costs and simplifies management.

In essence, KVM is a powerful, built-in Linux feature that enables efficient virtualization, allowing you to run multiple isolated computer systems on just one piece of physical hardware.

See Also

• Virtualization
• Hypervisor
• Virtual machine
• Linux kernel
• QEMU
• VPS
• Cloud computing
• Operating system

References

• Template:Cite web - Official KVM website (more technical, but good source).
• Template:Cite web - Explanation from a major Linux vendor using KVM.
• Template:Cite web - Documentation and explanation from another major Linux vendor.
• Template:Cite web - Website for the companion user-space tool.
• Template:Cite web - General explanation of virtualization (proprietary vendor, but good basic definition).