# QEMU — Open-Source Machine Emulator and Virtualizer

> A generic open-source machine emulator and virtualizer that can run operating systems for any architecture on any supported host.

## Install

Save in your project root:

# QEMU

## Quick Use
```bash
sudo apt install qemu-system-x86
# Create a disk and boot an ISO:
qemu-img create -f qcow2 disk.qcow2 20G
qemu-system-x86_64 -hda disk.qcow2 -cdrom ubuntu.iso -m 4096 -enable-kvm -boot d
```

## Introduction
QEMU (Quick Emulator) is an open-source machine emulator and virtualizer. In emulation mode it can run software built for one CPU architecture on another. When paired with KVM on Linux, it becomes a high-performance hypervisor capable of running virtual machines at near-native speed. QEMU underpins many cloud platforms and virtualization tools.

## What QEMU Does
- Emulates full systems including CPU, memory, storage, and network devices for 20+ architectures
- Provides near-native VM performance when combined with KVM hardware acceleration
- Creates and manages disk images in qcow2, raw, vmdk, and other formats
- Supports live migration of running VMs between physical hosts
- Offers user-mode emulation for running individual binaries built for foreign architectures

## Architecture Overview
QEMU uses a Tiny Code Generator (TCG) for dynamic binary translation when emulating foreign architectures. With KVM enabled, it offloads CPU virtualization to the Linux kernel via `/dev/kvm`, handling only device emulation in userspace. QEMU models each VM as a process with threads for vCPUs and I/O. Virtio paravirtualized devices provide efficient disk, network, and memory balloon interfaces between guest and host.

## Self-Hosting & Configuration
- Install via package managers: `apt install qemu-system` or `dnf install qemu-kvm`
- Enable KVM by loading the `kvm_intel` or `kvm_amd` kernel module
- Create disk images with `qemu-img create -f qcow2` for copy-on-write snapshots
- Pass `-enable-kvm -cpu host` for best performance on compatible hardware
- Use `-nic user` for simple NAT networking or `-nic tap` for bridged access

## Key Features
- Supports x86, ARM, RISC-V, MIPS, PowerPC, s390x, and many more architectures
- Snapshot and rollback of entire VM state including memory and disk
- Live migration for moving VMs between hosts with minimal downtime
- Virtio device framework for high-throughput paravirtualized I/O
- Serves as the backend for libvirt, Proxmox, OpenStack, and Firecracker

## Comparison with Similar Tools
- **VirtualBox** — desktop-focused with a GUI; QEMU is more flexible and powers production cloud infrastructure
- **VMware ESXi** — enterprise hypervisor with proprietary management; QEMU/KVM is free and equally performant
- **Firecracker** — micro-VM engine built on KVM for serverless; QEMU provides full system emulation with richer device support
- **Hyper-V** — Windows-native hypervisor; QEMU/KVM is the Linux standard and supports cross-architecture emulation

## FAQ
**Q: How does QEMU relate to KVM?**
A: KVM is a Linux kernel module that provides hardware virtualization. QEMU uses KVM for CPU acceleration and handles device emulation, networking, and disk I/O.

**Q: Can QEMU run macOS guests?**
A: Technically possible with the right configuration, but Apple restricts macOS to Apple hardware in their EULA.

**Q: What is qcow2?**
A: QEMU Copy-On-Write v2 is a disk image format supporting snapshots, compression, and thin provisioning.

**Q: Is QEMU suitable for production workloads?**
A: Yes. With KVM acceleration, QEMU powers major cloud providers and enterprise virtualization platforms like OpenStack and Proxmox.

## Sources
- https://github.com/qemu/qemu
- https://www.qemu.org/docs/master/

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Source: https://tokrepo.com/en/workflows/6cd0348b-43e8-11f1-9bc6-00163e2b0d79
Author: AI Open Source