KVM and QEMU Basics

KVM (Kernel-based Virtual Machine) and QEMU (Quick Emulator) are essential components in the Linux virtualization stack, allowing users to run multiple virtual machines (VMs) on a single physical host.

KVM turns the Linux kernel into a hypervisor, while QEMU provides hardware emulation.

• Hypervisor: Software that creates and manages VMs.
• Guest OS: Operating system running inside a VM.
• Host OS: The main operating system running on the physical machine.
• Virtual Machine: A software emulation of a physical computer.

To install KVM and QEMU on a Debian-based system, execute the following commands:

sudo apt update
sudo apt install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils

On Red Hat-based systems, use:

sudo yum install @virt

Finally, check if KVM is installed successfully:

sudo kvm-ok

To create a VM with QEMU, you can use the following command:

qemu-system-x86_64 -hda /path/to/disk/image.img -m 2048 -smp 2 -net nic -net user

Where:

• -hda: Specifies the hard disk image file.
• -m: Allocates RAM to the VM (in MB).
• -smp: Sets the number of CPU cores.
• -net: Configures networking.

You can manage VMs with the virt-manager GUI or command-line tools like virsh.

Common commands:

• virsh start - Starts a VM.
• virsh shutdown - Gracefully shuts down a VM.
• virsh list - Lists all VMs.

Follow these best practices when using KVM and QEMU:

• Always keep your hypervisor and VMs updated.
• Use bridged networking for better performance.
• Allocate resources carefully to avoid over-provisioning.
• Regularly backup VM images to prevent data loss.