---
tags:
  - nix
  - qemu
---
`nixos-buildvm` dumps a shell script that:

Creates an empty filesystem image (qcow2) using qemu-img

A qemu KVM VM is started
```
exec /nix/store/5v70rrpzv3jwcg7ixa5k9zk0j0lai3nd-qemu-host-cpu-only-9.1.2/bin/qemu-kvm -cpu max \
    -name tarrel \
    -m 1024 \
    -smp 1 \
    -device virtio-rng-pci \
    -net nic,netdev=user.0,model=virtio -netdev user,id=user.0,"$QEMU_NET_OPTS" \
    -virtfs local,path=/nix/store,security_model=none,mount_tag=nix-store \
    -virtfs local,path="${SHARED_DIR:-$TMPDIR/xchg}",security_model=none,mount_tag=shared \
    -virtfs local,path="$TMPDIR"/xchg,security_model=none,mount_tag=xchg \
    -drive cache=writeback,file="$NIX_DISK_IMAGE",id=drive1,if=none,index=1,werror=report -device virtio-blk-pci,bootindex=1,drive=drive1,serial=root \
    -device virtio-keyboard \
    -usb \
    -device usb-tablet,bus=usb-bus.0 \
    -kernel ${NIXPKGS_QEMU_KERNEL_tarrel:-/nix/store/47zad70cn0qi0pkvv21b43qwiis50lis-nixos-system-tarrel-24.11pre-git/kernel} \
    -initrd /nix/store/aqbxrnk7jg7piy7g85npm9xysmrvlihw-initrd-linux-6.6.71/initrd \
    -append "$(cat /nix/store/47zad70cn0qi0pkvv21b43qwiis50lis-nixos-system-tarrel-24.11pre-git/kernel-params) init=/nix/store/47zad70cn0qi0pkvv21b43qwiis50lis-nixos-system-tarrel-24.11pre-git/init regInfo=/nix/store/fii757n9q5f603hmqfdni49lskni93cb-closure-info/registration console=ttyS0,115200n8 console=tty0 $QEMU_KERNEL_PARAMS" \
    $QEMU_OPTS \
    "$@"
```

It shared 3 dirs from the host with the guest most notably the nix store. The disk image is used as a [[Wri]]