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Getting Started with Firecracker



If you need an opinionated way of running Firecracker, create an i3.metal instance using Ubuntu 18.04 on EC2. Firecracker uses KVM and needs read/write access that can be granted as shown below:

sudo setfacl -m u:${USER}:rw /dev/kvm

The generic requirements are explained below:

  • Linux 4.14+

    Firecracker currently supports physical Linux x86_64 hosts, running kernel version 4.14 or later.

  • KVM

    Please make sure that:

    1. you have KVM enabled in your Linux kernel, and
    2. you have read/write access to /dev/kvm. If you need help setting up access to /dev/kvm, you should check out Appendix A.
Click here to see a BASH script that will check if your system meets the basic requirements to run Firecracker.
err=""; \
[ "$(uname) $(uname -m)" = "Linux x86_64" ] \
  || err="ERROR: your system is not Linux x86_64."; \
[ -r /dev/kvm ] && [ -w /dev/kvm ] \
  || err="$err\nERROR: /dev/kvm is innaccessible."; \
(( $(uname -r | cut -d. -f1)*1000 + $(uname -r | cut -d. -f2) >= 4014 )) \
  || err="$err\nERROR: your kernel version ($(uname -r)) is too old."; \
dmesg | grep -i "hypervisor detected" \
  && echo "WARNING: you are running in a virtual machine. Firecracker is not well tested under nested virtualization."; \
[ -z "$err" ] && echo "Your system looks ready for Firecracker!" || echo -e "$err"

Getting the Firecracker Binary

Firecracker is linked statically against musl, having no library dependencies. You can just download the latest binary from our release page, and run it on your x86_64 Linux machine.

On the EC2 instance, this binary can be downloaded as:

curl -LOJ${latest}/firecracker-v${latest}

If, instead, you'd like to build Firecracker yourself, you should check out the Building From Source section in this doc.

Running Firecracker

In production, Firecracker is designed to be run securely, inside an execution jail, carefully set up by the jailer binary. This is how our integration test suite does it. However, if you just want to see Firecracker booting up a guest Linux machine, you can do that as well.

First, make sure you have the firecracker binary available - either downloaded from our release page, or built from source.

Next, you will need an uncompressed Linux kernel binary, and an ext4 file system image (to use as rootfs). You can use these files from our microVM image S3 bucket: kernel, and rootfs.

Now, let's open up two shell prompts: one to run Firecracker, and another one to control it (by writing to the API socket). For the purpose of this guide, make sure the two shells run in the same directory where you placed the firecracker binary.

In your first shell:

  • make sure Firecracker can create its API socket:
rm -f /tmp/firecracker.socket
  • then, start Firecracker:
./firecracker --api-sock /tmp/firecracker.socket

In your second shell prompt:

  • get the kernel and rootfs, if you don't have any available:

    curl -fsSL -o hello-vmlinux.bin
    curl -fsSL -o hello-rootfs.ext4
  • set the guest kernel:

    curl --unix-socket /tmp/firecracker.socket -i \
        -X PUT 'http://localhost/boot-source'   \
        -H 'Accept: application/json'           \
        -H 'Content-Type: application/json'     \
        -d '{
            "kernel_image_path": "./hello-vmlinux.bin",
            "boot_args": "console=ttyS0 reboot=k panic=1 pci=off"
  • set the guest rootfs:

    curl --unix-socket /tmp/firecracker.socket -i \
        -X PUT 'http://localhost/drives/rootfs' \
        -H 'Accept: application/json'           \
        -H 'Content-Type: application/json'     \
        -d '{
            "drive_id": "rootfs",
            "path_on_host": "./hello-rootfs.ext4",
            "is_root_device": true,
            "is_read_only": false
  • start the guest machine:

    curl --unix-socket /tmp/firecracker.socket -i \
        -X PUT 'http://localhost/actions'       \
        -H  'Accept: application/json'          \
        -H  'Content-Type: application/json'    \
        -d '{
            "action_type": "InstanceStart"

Going back to your first shell, you should now see a serial TTY prompting you to log into the guest machine. If you used our hello-rootfs.ext4 image, you can login as root, using the password root.

When you're done, issuing a reboot command inside the guest will shutdown Firecracker gracefully. This is because, since microVMs are not designed to be restarted, and Firecracker doesn't currently implement guest power management, we're using the keyboard reset action as a shut down switch.

Note: the default microVM will have 1 vCPU and 128 MiB RAM. If you wish to customize that (say, 2 vCPUs and 1024MiB RAM), you can do so before issuing the InstanceStart call, via this API command:

curl --unix-socket /tmp/firecracker.socket -i  \
    -X PUT 'http://localhost/machine-config' \
    -H 'Accept: application/json'            \
    -H 'Content-Type: application/json'      \
    -d '{
        "vcpu_count": 2,
        "mem_size_mib": 1024

Building From Source

The quickest way to build and test Firecracker is by using our development tool (tools/devtool). It employs a Docker container to store the software toolchain used throughout the development process. If you need help setting up Docker on your system, you can check out Appendix B: Setting Up Docker.

Getting the Firecracker Sources

Get a copy of the Firecracker sources by cloning our GitHub repo:

git clone

All development happens on the master branch and we use git tags to mark releases. If you are interested in a specific release (e.g. v0.10.1), you can check it out with:

git checkout tags/v0.10.1

Building Firecracker

Within the Firecracker repository root directory:

tools/devtool build

This will build and place the two Firecracker binaries at build/debug/firecracker and build/debug/jailer. The default build profile is debug. If you want to build the release binaries (optimized and stripped of debug info), use the --release option:

tools/devtool build --release

Extensive usage information about devtool and its various functions and arguments is available via:

tools/devtool --help

Running the Integration Test Suite

You can also use our development tool to run the integration test suite:

tools/devtool test

Please note that the test suite is designed to ensure our SLA parameters as measured on EC2 .metal instances and, as such, some performance tests may fail when run on a regular desktop machine. Specifically, don't be alarmed if you see tests/integration_tests/performance/ failing when not run on an EC2 .metal instance.

Appendix A: Setting Up KVM Access

Some Linux distributions use the kvm group to manage access to /dev/kvm, while others rely on access control lists. If you have the ACL package for your distro installed, you can grant your user access via:

sudo setfacl -m u:${USER}:rw /dev/kvm

Otherwise, if access is managed via the kvm group:

[ $(stat -c "%G" /dev/kvm) = kvm ] && sudo usermod -aG kvm ${USER} && echo "Access granted."

If none of the above works, you will need to either install the file system ACL package for your distro and use the setfacl command as above, or run Firecracker as root (via sudo).

You can check if you have access to /dev/kvm with:

[ -r /dev/kvm ] && [ -w /dev/kvm ] && echo "OK" || echo "FAIL"

Note: If you've just added your user to the kvm group via usermod, don't forget to log out and then back in, so this change takes effect.

Appendix B: Setting Up Docker

To get Docker, you can either use the official Docker install instructions , or the package manager available on your specific Linux distribution:

  • on Debian / Ubuntu

    sudo apt-get update
    sudo apt-get install
  • on Fedora / CentOS / RHEL / Amazon Linux

    sudo yum install docker

Then, for any of the above, you will need to start the Docker daemon and add your user to the docker group.

sudo systemctl start docker
sudo usermod -aG docker $USER

Don't forget to log out and then back in again, so that the user change takes effect.

If you wish to have Docker started automatically after boot, you can:

sudo systemctl enable docker

We recommend testing your Docker configuration by running a lightweight test container and checking for net connectivity:

docker pull alpine
docker run --rm -it alpine ping -c 3