The Linux kernel’s kernel-based virtual machine is KVM, short for Kernel-based Virtual Machine.
KVM is an open-source virtualization module integrated into the Linux kernel. With suitable processor virtualization extensions, such as Intel VT-x or AMD-V, it lets Linux act as a hypervisor and run guest operating systems in virtual machines.
KVM itself supplies the kernel-side virtualization interface and uses hardware-assisted CPU virtualization, but it does not emulate every device a guest might need. A userspace virtual machine monitor such as QEMU commonly works with KVM to provide device emulation, firmware, and machine-management functions. This is why “QEMU/KVM” is a frequent pairing, even though the two projects have different roles.
KVM first appeared publicly in 2006 after development at Qumranet and was merged into the mainline Linux kernel in version 2.6.20, released on 5 February 2007. VirtualBox, Hyper-V, and Xen are separate virtualization products or hypervisor technologies. KVM can host many guest systems and supports features such as VirtIO devices, live migration, and dynamic virtual CPU or memory management through its surrounding userspace tools.