💾 Archived View for elektito.com › gemlog › 5-quick-qemu captured on 2023-12-28 at 15:27:34. Gemini links have been rewritten to link to archived content

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Commands to Quickly Get a qemu VM

I needed to setup a VM for testing my deployment scripts, and since I was rather tired of vagrant for various reasons, I decided to just use qemu. Here's what I did.

First, I need a cloud image. I'm gonna use the latest Ubuntu LTS as of now:

wget https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img

Then I'll create an image based on that:

qemu-img create -f qcow2 -F qcow2 -b jammy-server-cloudimg-amd64.img foo.qcow2 16G

This will get you an image file aptly named foo.qcow2. Then I'll create a file named metadata.yaml:

instance-id: test-vm1
local-hostname: cloudimg

And another named user-data.yaml:

#cloud-config
users:
  - default
  - name: user
    ssh_authorized_keys:
      - ssh-rsa ... user@test
    sudo: ALL=(ALL) NOPASSWD:ALL
    shell: /bin/bash
mounts:
  - [ foo0, /mnt, "9p", "trans=virtio,version=9p2000.L"]

Replace "..." with your ssh public key. Now we'll create a seed image based on those files:

cloud-localds seed.img user-data.yaml metadata.yaml

On ubuntu, you can get the cloud-localds command by installing the cloud-image-utils package.

Now run the VM:

qemu-system-x86_64 \
    -machine accel=kvm,type=q35 \
    -cpu host \
    -m 2G \
    -nographic \
    -device virtio-net-pci,netdev=net0 \
    -netdev user,id=net0,hostfwd=tcp::2222-:22 \
    -drive if=virtio,format=qcow2,file=foo.qcow2 \
    -drive if=virtio,format=raw,file=seed.img \
    -virtfs local,path=/home/mostafa/source/elektito.com/,mount_tag=foo0,security_model=mapped-xattr,id=foo0 \
    -snapshot

In the virtfs flag, the foo0 value passed as "mount_tag" should be the same as the device name we set in the mounts section of user-data.yaml. The id value (which I'm passing the same value to) is unused as far as I can tell, but I'm setting it to the same value just to be safe.

After the VM starts, you can open another terminal and ssh into the VM by running:

ssh -p 2222 user@0.0.0.0

When you're done with the VM, you can break out of qemu emulation (in the first terminal), by pressing "C-a c", and then typing "quit".