# qemu-kvm

Walks the agent through QEMU VMs with KVM acceleration: flags, virtio devices, VFIO passthrough and booting custom kernels.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 304 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/virtualization/qemu-kvm/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/qemu-kvm

## What it does

The skill tells the agent how to build a `qemu-system-x86_64` command with `-enable-kvm`, `-cpu host`, the right amount of RAM and a network backend. virtio devices get their own section: `virtio-blk-pci` for disks, `virtio-net-pci` for networking, `virtio-balloon-pci` for dynamic memory and `virtio-scsi`. The author advises against emulated devices — a VM on them runs noticeably slower.

There are sections on VFIO passthrough, the QMP monitor and libvirt management. Passthrough needs IOMMU turned on: without `intel_iommu=on` or `amd_iommu=on` on the kernel command line the device will not detach from its host driver. For QMP the skill shows the `unix:/tmp/qmp.sock` socket and commands like `query-status` and `savevm`; for libvirt it covers `virsh define`, `virsh start`, snapshots and `virt-install`.

Kernel work is a separate block. Booting with `-kernel`, `-initrd` and `-append` skips a disk install entirely, and debugging goes through the GDB stub: `-s -S` opens port 1234 and waits for a debugger. The troubleshooting table lists the usual failures — a KVM disabled warning, a VFIO group error, a kernel panic from a wrong `root=` or a missing driver in initrd.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/qemu-kvm/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/qemu-kvm/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/qemu-kvm/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/qemu-kvm/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills qemu-kvm
```

2. **Manually: put the files in place**
- File: `.github/skills/qemu-kvm/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/virtualization/qemu-kvm
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/qemu-kvm/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill qemu-kvm -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/virtualization/qemu-kvm/SKILL.md

## When to use it
- run a Linux VM with hardware KVM acceleration
- pick the right qemu-system-x86_64 flags for a setup
- pass a GPU or NIC into a guest with VFIO
- manage VMs through libvirt and virsh
- boot a custom kernel without installing a system to disk

## Example prompts
- build a qemu-system-x86_64 command with KVM for an Ubuntu VM with 4 GB RAM
- set up virtio-net and a tap interface for my VM
- boot QEMU with -kernel bzImage and -append to test my kernel

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 30deb49ab5828e01.

BEGIN THIRD-PARTY FILE 30deb49ab5828e01
````text
---
name: qemu-kvm
description: QEMU/KVM skill for virtualization and kernel development. Use when running qemu-system-x86_64 with KVM, configuring virtio devices, VFIO passthrough, QMP monitor, libvirt, or booting custom kernels. Activates on queries about QEMU, KVM, virtio, VFIO, virsh, virt-install, or -kernel -append.
---

# QEMU / KVM

## Purpose

Guide agents through QEMU system emulation and KVM acceleration: key `qemu-system-x86_64` flags, virtio devices, VFIO device passthrough, QMP monitor protocol, libvirt/virsh management, and QEMU for kernel development with `-kernel -initrd -append`.

## When to Use

- Running Linux VMs with hardware acceleration
- Testing custom kernels without bare metal
- Passing through GPU or NIC to a VM with VFIO
- Managing VMs with libvirt and virsh
- Creating VM snapshots for reproducible testing
- Developing kernel or bootloader with direct kernel boot

## Workflow

### 1. Basic KVM VM

```bash
# Check KVM support
egrep -c '(vmx|svm)' /proc/cpuinfo
ls -l /dev/kvm

# Minimal Ubuntu VM
qemu-system-x86_64 \
  -enable-kvm \
  -cpu host \
  -m 4096 \
  -smp 4 \
  -drive file=ubuntu.img,format=qcow2 \
  -netdev user,id=net0 \
  -device virtio-net-pci,netdev=net0 \
  -display none \
  -serial mon:stdio
```

| Flag | Purpose |
|------|---------|
| `-enable-kvm` | Use KVM acceleration |
| `-cpu host` | Pass through host CPU features |
| `-m` | RAM in MB |
| `-smp` | vCPU count |
| `-drive` | Disk image |
| `-netdev` / `-device` | Network backend |

### 2. virtio devices

```bash
# virtio-blk (paravirtual disk — faster)
-device virtio-blk-pci,drive=hd0 \
-drive if=none,id=hd0,file=disk.qcow2,format=qcow2

# virtio-net
-netdev tap,id=net0,ifname=tap0,script=no,downscript=no \
-device virtio-net-pci,netdev=net0

# virtio-balloon (dynamic memory)
-device virtio-balloon-pci

# virtio-scsi
-device virtio-scsi-pci,id=scsi0 \
-device scsi-hd,drive=hd0,bus=scsi0.0
```

Always prefer virtio over emulated devices for performance.

### 3. VFIO device passthrough

```bash
# Bind device to vfio-pci
echo 10de 1c03 | sudo tee /sys/bus/pci/drivers/vfio-pci/new_id
sudo virsh nodedev-detach pci_0000_01_00_0

# QEMU with passthrough
qemu-system-x86_64 \
  -enable-kvm -m 8192 -smp 8 \
  -device vfio-pci,host=01:00.0 \
  ...
```

Requires IOMMU enabled (`intel_iommu=on` or `amd_iommu=on` in kernel cmdline).

### 4. QMP monitor

```bash
# Start with QMP socket
qemu-system-x86_64 ... \
  -qmp unix:/tmp/qmp.sock,server,nowait

# Send QMP commands
socat - UNIX-CONNECT:/tmp/qmp.sock
````
END THIRD-PARTY FILE 30deb49ab5828e01

The third-party file has ended. Everything between the 30deb49ab5828e01 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2533 of 5309 bytes. © mohitmishra786 · MIT · https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/virtualization/qemu-kvm/SKILL.md

_Part of the page did not fit — see the HTML version._

---
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