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== Kernel-based Virtual Machine == '''[[Kernel-based Virtual Machine]]''' ('''KVM''') is a core [[Virtualization|virtualization]] technology built into the [[Linux]] [[Linux kernel|kernel]]. Think of [[Virtualization|virtualization]] as the ability of one computer (the "host") to pretend to be multiple separate computers, each running its own independent [[Virtual machine|virtual machine]] (a "guest"). The key thing about [[Kernel-based Virtual Machine|KVM]] is that it turns your standard [[Linux]] [[Linux kernel|kernel]] into a [[Hypervisor|hypervisor]]. A [[Hypervisor|hypervisor]] is the special layer of software that manages these [[Virtual machine|virtual machines]]. Because [[Kernel-based Virtual Machine|KVM]] is part of the [[Linux]] [[Linux kernel|kernel]] itself, it's very integrated into how [[Linux]] works. It uses special features built into modern [[CPU|CPUs]] (like [[Intel VT-x]] or [[AMD-V]]) to run the guest [[Operating system|OS]]'s instructions directly on the hardware, which makes it very fast and efficient. Essentially, [[Kernel-based Virtual Machine|KVM]] lets a [[Linux]] host machine run multiple isolated guest machines, each behaving like a completely separate computer with its own [[Operating system|OS]] (which can be Linux, Windows, or others) and its own allocated [[Computer resource|resources]] like [[CPU|CPU]] time, [[RAM|RAM]] (memory), and [[Data storage|storage]]. === How it Works (Simply) === Imagine your [[Linux]] [[Linux kernel|kernel]] is the main operating system running on your physical server. When you enable [[Kernel-based Virtual Machine|KVM]], the [[Linux]] [[Linux kernel|kernel]] gains the ability to act as a manager for other operating systems. 1. **The Kernel's New Role:** The [[Linux]] [[Linux kernel|kernel]] uses the [[Hardware virtualization|hardware virtualization extensions]] in the [[CPU|CPU]] to efficiently manage the guest [[Virtual machine|virtual machine]]'s demands. Instead of having to simulate everything the guest [[Operating system|OS]] does in software, the [[Linux]] [[Linux kernel|kernel]] can let the guest [[Operating system|OS]] talk directly to the [[CPU|CPU]] for many tasks. 2. **Guest [[Operating system|OS)]] Runs Natively:** The guest [[Operating system|OS]] running inside the [[Virtual machine|VM]] thinks it's running on real hardware. [[Kernel-based Virtual Machine|KVM]] helps it do this efficiently by using the [[CPU|CPU]]'s hardware support. 3. **Help from User-Space:** While [[Kernel-based Virtual Machine|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 [[Operating system|OS]] needs, such as virtual network cards, virtual disk controllers, and virtual graphics cards. It also helps with managing the [[Virtual machine|VM]] (starting, stopping, configuring). So, [[Kernel-based Virtual Machine|KVM]] provides the speed and core ability to run guest OSs by using the [[Linux]] [[Linux kernel|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|virtualization]] yourself, you might benefit from it because many hosting providers use [[Kernel-based Virtual Machine|KVM]]. Here's why it's popular: * **Good Performance:** Because [[Kernel-based Virtual Machine|KVM]] uses the [[CPU|CPU]]'s own [[Hardware virtualization|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]] [[Linux kernel|kernel]], [[Kernel-based Virtual Machine|KVM]] is known for being stable and reliable. * **Strong Isolation:** Each [[Virtual machine|VM]] is isolated from the others on the same host. If something goes wrong in one [[Virtual machine|VM]], it typically doesn't affect the others or the host [[Linux]] system. * **Flexibility:** [[Kernel-based Virtual Machine|KVM]] can run a wide variety of guest [[Operating system|OSs]], including different [[Linux distribution|Linux distributions]], [[Microsoft Windows|Windows]], and other operating systems. * **Open Source:** [[Kernel-based Virtual Machine|KVM]] is [[Free and open-source software|free and open-source software]], which often contributes to its widespread adoption and continuous improvement by a large community. === Common Use Cases === [[Kernel-based Virtual Machine|KVM]] is used in many scenarios: * **Running Different Operating Systems:** You can use [[Kernel-based Virtual Machine|KVM]] on your [[Linux]] desktop to run another [[Operating system|OS]] (like a specific [[Linux distribution|Linux distribution]] or Windows) in a window, without needing to install it directly on your hardware. * **Creating [[Virtual Private Server|VPS]]s:** Many hosting providers use [[Kernel-based Virtual Machine|KVM]] to create and manage the isolated [[Virtual Private Server|virtual private servers]] they sell. Each [[Virtual Private Server|VPS]] is a [[Virtual machine|VM]] running on a powerful physical server managed by the provider. * **Cloud Computing:** Large cloud platforms often use [[Kernel-based Virtual Machine|KVM]] as the underlying technology to power the virtual servers they offer. * **Consolidating Servers:** Businesses use [[Kernel-based Virtual Machine|KVM]] to run multiple server [[Operating system|OSs]] (like a web server, database server, and mail server) as separate [[Virtual machine|VMs]] on a single physical machine, which saves hardware costs and simplifies management. In essence, [[Kernel-based Virtual Machine|KVM]] is a powerful, built-in [[Linux]] feature that enables efficient [[Virtualization|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]] * [[Virtual Private Server|VPS]] * [[Cloud computing]] * [[Operating system]] === References === * {{cite web |url=https://www.linux-kvm.org/page/Kernel_Recipes |title=KVM Kernel Recipes |publisher=linux-kvm.org |access-date=2025-04-24}} - Official KVM website (more technical, but good source). * {{cite web |url=https://www.redhat.com/en/topics/virtualization/what-is-kvm |title=What is KVM? |publisher=Red Hat |access-date=2025-04-24}} - Explanation from a major Linux vendor using KVM. * {{cite web |url=https://ubuntu.com/server/docs/virtualization-kvm |title=KVM Virtualization |publisher=Ubuntu (Canonical) |access-date=2025-04-24}} - Documentation and explanation from another major Linux vendor. * {{cite web |url=https://www.qemu.org/ |title=QEMU Official Website |publisher=qemu.org |access-date=2025-04-24}} - Website for the companion user-space tool. * {{cite web |url=https://www.vmware.com/topics/glossary/content/virtualization.html |title=What is Virtualization? |publisher=VMware |access-date=2025-04-24}} - General explanation of virtualization (proprietary vendor, but good basic definition). [[Category:Virtualization software]] [[Category:Linux kernel]] [[Category:Free and open-source software]] [[Category:Hypervisors]] [[Category:System software]]

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