grub imagelet to start VMs from an image without bootloader

0-image.sh

# Create the grub boot image
grub-mkimage -O i386-pc -o grub.img -c grub.cfg \
    at_keyboard configfile biosdisk ext2 linux test serial halt minicmd terminal cat acpi


# to create the unbootable linux image, no partitions
qemu-img create -f qcow2 unbootable.img 10G
sudo modprobe nbd max_part=16
sudo qemu-nbd -c /dev/nbd0 unbootable.img
sudo mkfs.ext4 -L ROOT /dev/nbd0
sudo mount /dev/nbd0 /mnt/

sudo debootstrap --arch=amd64 --variant=minbase --include=linux-image-amd64,iproute2,vim \
           jessie /mnt http://debian.blizoo.mk/debian
sudo systemd-nspawn --setenv=RUNLEVEL=1 -D /mnt /usr/bin/passwd

sudo umount /mnt
sudo qemu-nbd -d /dev/nbd0


# to run a VM
qemu-system-x86_64 -enable-kvm -kernel grub.img -hda unbootable.img 
 # optional: -drive file=unbootable.img,if=virtio
 # optional: -net user -net nic,model=virtio

1-grub.cfg

linux (hd0)/vmlinuz root=LABEL=ROOT rw
initrd (hd0)/initrd.img
boot

2-network.sh

sudo systemd-nspawn -D /mnt
systemctl enable systemd-networkd
systemctl enable systemd-resolved

ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
# or in systemd >216 modify /etc/nsswitch.conf to have
# hosts: files mymachines resolve myhostname

cat > /etc/systemd/network/wired.network <<EOF
[Match]
Name=eth0

[Network]
DHCP=yes
EOF