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jvns/firecracker-hello-world.sh Secret

Last active February 18, 2026 07:41
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firecracker-hello-world.sh
set -eu
[ -e hello-vmlinux.bin ] || wget https://s3.amazonaws.com/spec.ccfc.min/img/hello/kernel/hello-vmlinux.bin
[ -e hello-rootfs.ext4 ] || wget -O hello-rootfs.ext4 https://raw.githubusercontent.com/firecracker-microvm/firecracker-demo/ec271b1e5ffc55bd0bf0632d5260e96ed54b5c0c/xenial.rootfs.ext4
[ -e hello-id_rsa ] || wget -O hello-id_rsa https://raw.githubusercontent.com/firecracker-microvm/firecracker-demo/ec271b1e5ffc55bd0bf0632d5260e96ed54b5c0c/xenial.rootfs.id_rsa
TAP_DEV="fc-88-tap0"
# set up the kernel boot args
MASK_LONG="255.255.255.252"
MASK_SHORT="/30"
FC_IP="169.254.0.21"
TAP_IP="169.254.0.22"
FC_MAC="02:FC:00:00:00:05"
KERNEL_BOOT_ARGS="ro console=ttyS0 noapic reboot=k panic=1 pci=off nomodules random.trust_cpu=on"
KERNEL_BOOT_ARGS="${KERNEL_BOOT_ARGS} ip=${FC_IP}::${TAP_IP}:${MASK_LONG}::eth0:off"
ip link del "$TAP_DEV" 2> /dev/null || true
ip tuntap add dev "$TAP_DEV" mode tap
sysctl -w net.ipv4.conf.${TAP_DEV}.proxy_arp=1 > /dev/null
sysctl -w net.ipv6.conf.${TAP_DEV}.disable_ipv6=1 > /dev/null
ip addr add "${TAP_IP}${MASK_SHORT}" dev "$TAP_DEV"
ip link set dev "$TAP_DEV" up
cat <<EOF > vmconfig.json
{
"boot-source": {
"kernel_image_path": "hello-vmlinux.bin",
"boot_args": "$KERNEL_BOOT_ARGS"
},
"drives": [
{
"drive_id": "rootfs",
"path_on_host": "hello-rootfs.ext4",
"is_root_device": true,
"is_read_only": false
}
],
"network-interfaces": [
{
"iface_id": "eth0",
"guest_mac": "$FC_MAC",
"host_dev_name": "$TAP_DEV"
}
],
"machine-config": {
"vcpu_count": 2,
"mem_size_mib": 1024,
"ht_enabled": false
}
}
EOF
firecracker --no-api --config-file vmconfig.json
@bharadwaj6
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bharadwaj6 commented May 29, 2022 •
edited
Loading

@alexellis The script will work if you use the images provided in firecracker repo readme.

Instead of

[ -e hello-vmlinux.bin ] || wget https://s3.amazonaws.com/spec.ccfc.min/img/hello/kernel/hello-vmlinux.bin
[ -e hello-rootfs.ext4 ] || wget -O hello-rootfs.ext4 https://raw.githubusercontent.com/firecracker-microvm/firecracker-demo/ec271b1e5ffc55bd0bf0632d5260e96ed54b5c0c/xenial.rootfs.ext4
[ -e hello-id_rsa ] || wget -O hello-id_rsa https://raw.githubusercontent.com/firecracker-microvm/firecracker-demo/ec271b1e5ffc55bd0bf0632d5260e96ed54b5c0c/xenial.rootfs.id_rsa

Use

arch=`uname -m`
dest_kernel="hello-vmlinux.bin"
dest_rootfs="hello-rootfs.ext4"
image_bucket_url="https://s3.amazonaws.com/spec.ccfc.min/img/quickstart_guide/$arch"

if [ ${arch} = "x86_64" ]; then
    kernel="${image_bucket_url}/kernels/vmlinux.bin"
    rootfs="${image_bucket_url}/rootfs/bionic.rootfs.ext4"
elif [ ${arch} = "aarch64" ]; then
    kernel="${image_bucket_url}/kernels/vmlinux.bin"
    rootfs="${image_bucket_url}/rootfs/bionic.rootfs.ext4"
else
    echo "Cannot run firecracker on $arch architecture!"
    exit 1
fi

if [ ! -f $dest_kernel ]; then
    echo "Kernel not found, downloading $kernel..."
    curl -fsSL -o $dest_kernel $kernel
    echo "Saved kernel file to $dest_kernel."
fi

if [ ! -f $dest_rootfs ]; then
    echo "Rootfs not found, downloading $rootfs..."
    curl -fsSL -o $dest_rootfs $rootfs
    echo "Saved root block device to $dest_rootfs."
fi

echo "Downloading public key file..."
[ -e hello-id_rsa ] || wget -O hello-id_rsa https://raw.githubusercontent.com/firecracker-microvm/firecracker-demo/ec271b1e5ffc55bd0bf0632d5260e96ed54b5c0c/xenial.rootfs.id_rsa
echo "Saved public key file."

@DimitrisCharisis
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DimitrisCharisis commented Dec 11, 2024

For anyone running the initial script and failing with "unknown field ht_enabled", have in mind that ht_enabled has been renamed to smt. See also https://github.com/search?q=repo%3Afirecracker-microvm%2Ffirecracker%20ht_enabled&type=code

@SerJaimeLannister
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SerJaimeLannister commented Dec 20, 2025

Can someone please provide me a script which "just works" as I am trying to tinker with firecracker but I just cannot seem to do so

Thanks and have a nice day to everyone involved, this script and the blog post seems fascinating to look at!

@tiebingzhang
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tiebingzhang commented Feb 4, 2026 •
edited
Loading

check out this gist for the most recently updated working version: https://gist.github.com/tiebingzhang/94a48798e508e65a7eac842a4c983c2f

@alexellis
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alexellis commented Feb 18, 2026

Folks that are really struggling with these old examples, should take a look at my Firecracker lab..

https://github.com/alexellis/firecracker-init-lab (completely free)

And if you want to cut out a lot of the low-level Linux primitives, and work straight with a stable, production-ready API with networking, we have that in https://slicervm.com - created in 2022 spun out from our work on actuated (CI runners for GitHub/GitLab/Jenkins.. etc).

The slicer video also has a microVMs section with three of my best video explainers/webinars.

Alex

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