Kernel-based Virtual Machine
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Kernel-based Virtual Machine (KVM)
Kernel-based Virtual Machine (KVM) is a core virtualization technology built into the Linux kernel. Think of virtualization as a single computer (the "host") pretending to be multiple separate computers, each running its own independent virtual machine (VM) or "guest."
KVM turns your standard Linux kernel into a hypervisor. A hypervisor is special software that manages these virtual machines. Because KVM is part of the Linux kernel, it's deeply integrated. It uses special features in modern CPUs (like Intel VT-x or AMD-V) to run the guest operating system's instructions directly on the hardware, making it very fast and efficient.
Essentially, KVM lets a Linux host machine run multiple isolated guest machines. Each guest acts like a separate computer with its own operating system (Linux, Windows, or others) and its own allocated resources like CPU time, RAM, and storage.
How KVM Works (Simply)
Imagine your Linux kernel is the main operating system on your physical server. When you enable KVM, the Linux kernel gains the ability to manage other operating systems.
The Kernel's New Role: The Linux kernel uses special hardware virtualization features in the CPU to efficiently manage the guest VM's demands. Instead of simulating everything the guest OS does in software, the Linux kernel can let the guest OS talk directly to the CPU for many tasks. Guest OS Runs Natively: The guest OS inside the VM thinks it's running on real hardware. KVM helps it do this efficiently by using the CPU's hardware support. Help from User-Space: While KVM provides the core ability to run guest OSs, user-space tools (like QEMU) work alongside it. QEMU, for example, helps create and manage the virtual hardware devices the guest OS needs, such as virtual network cards, disk controllers, and graphics cards. It also helps with starting, stopping, and configuring the VM. 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)
Even if you don't set up virtualization yourself, you likely benefit from it, as many hosting providers use KVM. Here's why it's popular:
Good Performance: Because KVM uses the CPU's hardware virtualization features, VMs running on it are generally very fast, often performing almost like 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 others on the same host. If one VM has a problem, it typically doesn't affect other VMs or the host Linux system. Flexibility: KVM can run a wide variety of guest operating systems, including different Linux distributions, Windows, and others. Open Source: KVM is free and open-source software, which contributes to its widespread adoption and continuous improvement by a large community.
Common Use Cases
KVM is used in many situations:
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 installing it directly on your hardware. Creating Virtual Private Servers (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. This 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.
