KVM (Kernel-based Virtual Machine) is a virtualization infrastructure built into the Linux kernel that turns it into a hypervisor. QEMU (Quick Emulator) is a machine emulator and virtualizer that can work standalone or with KVM.

Key differences:

• KVM: Provides hardware-accelerated virtualization by leveraging CPU virtualization extensions (Intel VT-x/AMD-V). It's a kernel module that handles CPU and memory virtualization.
• QEMU: Handles device emulation, I/O operations, and can run without hardware acceleration (though slower). When combined with KVM, QEMU handles device emulation while KVM provides CPU virtualization.

Together: KVM + QEMU provides a complete virtualization solution where KVM handles CPU/memory virtualization efficiently, and QEMU handles device emulation and VM management.

Hardware Requirements:

• CPU with virtualization extensions (Intel VT-x or AMD-V)
• Sufficient RAM (depends on VM requirements)
• Storage space for VM images

Software Requirements:

• Linux kernel with KVM modules (kvm, kvm_intel/kvm_amd)
• QEMU package installed
• libvirt (optional but recommended for management)

Verification commands:

# Check CPU virtualization support
egrep -c '(vmx|svm)' /proc/cpuinfo

# Check if KVM modules are loaded
lsmod | grep kvm

# Verify KVM device exists
ls -la /dev/kvm

Type 1 (Bare Metal) Hypervisors:

• Run directly on physical hardware
• Examples: VMware ESXi, Xen, Hyper-V Server
• Better performance, lower overhead

Type 2 (Hosted) Hypervisors:

• Run on top of an existing operating system
• Examples: VMware Workstation, VirtualBox
• More flexible but higher overhead

KVM Classification:
KVM is unique - it's technically a Type 1 hypervisor because it's integrated into the Linux kernel, allowing direct hardware access. However, it relies on the Linux kernel infrastructure, which some classify as Type 2 characteristics. Most consider KVM a Type 1 hypervisor due to its kernel-level integration and performance characteristics.

Ubuntu Installation:

# Update system
sudo apt update

# Install KVM and related packages
sudo apt install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils virt-manager

# Add user to libvirt group
sudo usermod -aG libvirt,kvm $USER

# Start and enable libvirt service
sudo systemctl start libvirtd
sudo systemctl enable libvirtd

CentOS/RHEL Installation:

# Install virtualization packages
sudo yum install qemu-kvm libvirt virt-install virt-manager

# Start and enable services
sudo systemctl start libvirtd
sudo systemctl enable libvirtd

# Add user to libvirt group
sudo usermod -aG libvirt $USER

Verification:

# Check KVM installation
sudo virt-host-validate
virsh list --all