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Firecracker Ubuntu 24.04 Rootfs Setup

This document describes the setup process for creating a Firecracker-compatible Ubuntu 24.04 rootfs image.

Files Created

Setup Steps

1. Build Docker Image

Build the Docker image with the following command:

docker build -t ubuntu-24.04 -f assets/rootfs/ubuntu-24.04.dockerfile .

2. Download Kernel and Complete Rootfs Setup

Run the setup script to mount and extract the rootfs:

./assets/rootfs/setup-firecracker-ubuntu24.sh

This script will:

  • Mount the ext4 image
  • Extract the rootfs tarball
  • Configure DNS resolution
  • Unmount the filesystem

3. Enable IP Forwarding

To enable networking for the Firecracker VM:

sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"
sudo iptables -P FORWARD ACCEPT

Using with firecracker-python SDK

Once the setup is complete, you can use the rootfs with the firecracker-python SDK:

from firecracker import MicroVM

# Create a VM with the Ubuntu 24.04 rootfs and kernel
vm = MicroVM(kernel_file='./firecracker-files/vmlinux-5.10.204', base_rootfs='./firecracker-files/rootfs.img')
vm.create()

# Connect to the VM using SSH
vm.connect(key_path='./ssh_keys/ubuntu-24.04')

Or use the sample script:

./examples/sample.py

Dockerfile Details

The assets/rootfs/ubuntu-24.04.dockerfile includes:

  • Ubuntu 24.04 base image
  • SSH server configuration
  • Systemd and init packages
  • Network tools (net-tools, iproute2, iputils-ping)
  • DNS utilities (dnsutils)
  • Cloud-init support
  • Text editors (nano, vim)
  • SSH public key for root access

Kernel Information

The setup script downloads the Firecracker kernel from the official S3 bucket:

  • Kernel URL: https://s3.amazonaws.com/spec.ccfc.min/firecracker-ci/v1.7/${ARCH}/vmlinux-5.10.204
  • Kernel Version: Linux 5.10.204
  • Architecture: Automatically detected based on your system (x86_64, aarch64, etc.)
  • Kernel File: ./firecracker-files/vmlinux-5.10.204

The kernel is compatible with Firecracker v1.7 and is pre-compiled for use with microVMs.

Notes

  • The rootfs image is 10GB in size
  • The default SSH key is ssh_keys/ubuntu-24.04 (private key)
  • DNS is configured to use Google's DNS (8.8.8.8)
  • The root user can login via SSH using the provided key

Troubleshooting

If you encounter permission issues during setup, ensure you have sudo access.

If the mount point already exists, the script will handle it automatically.

References