KVM, which stands for Kernel-based Virtual Machine, is an open-source virtualization technology for the Linux operating system. It allows you to run multiple virtual machines (VMs) on a single physical host machine. KVM leverages the hardware virtualization extensions present in modern processors to provide efficient and high-performance virtualization capabilities. Here's a more detailed explanation of KVM:
1. Hypervisor: KVM is a type 1 hypervisor, which means it runs directly on the physical hardware, providing a virtualization layer between the hardware and the virtual machines. This is in contrast to type 2 hypervisors, which run on top of a host operating system.
2. Kernel Integration: KVM is tightly integrated into the Linux kernel. It consists of a kernel module (kvm.ko) that turns the Linux kernel into a hypervisor. This integration allows KVM to take advantage of the kernel's stability, security, and performance features.
3. Hardware Virtualization Support: KVM relies on the hardware virtualization extensions present in modern CPUs, such as Intel's VT-x and AMD's AMD-V. These extensions enable KVM to create and manage virtual machines efficiently, with minimal overhead and near-native performance.
4. Management Tools: KVM provides several user-space tools for managing virtual machines. The most commonly used tool is `QEMU`, which is a user-space emulator that can run a wide range of guest operating systems. QEMU, in combination with KVM, offers hardware-assisted virtualization and is responsible for launching and managing VMs.
5. Libvirt: Libvirt is an additional management tool commonly used with KVM. It provides a higher-level interface for managing various virtualization technologies, including KVM. Libvirt offers a command-line tool (`virsh`) and various programming interfaces (APIs) for managing virtual machines.
6. Guest Operating Systems: KVM can run a wide range of guest operating systems, including various Linux distributions, Windows, and others. It provides good support for both Windows and Linux guests.
7. Performance: KVM is known for its excellent performance and near-native speed for virtualized workloads. This is because it leverages hardware virtualization extensions and is closely integrated with the Linux kernel, reducing overhead and resource contention.
8. Security: Since KVM runs as part of the Linux kernel, it inherits the security features of the host operating system. Additionally, KVM's design minimizes the attack surface, making it a secure choice for virtualization.
9. Open Source: KVM is open-source software released under the GNU General Public License (GPL). This means it's freely available, and the source code is accessible for modification and improvement.
In summary, KVM is a powerful and efficient virtualization technology for Linux that leverages hardware virtualization extensions and is deeply integrated into the Linux kernel. It's commonly used in data centers and cloud environments to run multiple virtual machines on a single physical host, providing a cost-effective and flexible solution for virtualization needs.