Pin Docker-cpu FROM ubuntu:20.04

[glenn-jocher]

Pin FROM ubuntu:20.04

🛠️ PR Summary

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🌟 Summary

Update and simplify the YOLOv5 CPU Dockerfile.

📊 Key Changes

• 🚢 Switched the base Docker image from ubuntu:latest to ubuntu:20.04.
• ✂️ Removed unnecessary steps for installing Python 3.9 since Ubuntu 20.04 comes with Python 3.8 by default.
• 🔧 Changed python commands from python3.9 to the default python3.
• 🧹 Cleaned up the installation process, removing more complex setup for a simpler one.

🎯 Purpose & Impact

• 🔄 Ensures compatibility by using a more stable version of Ubuntu rather than the latest, which can vary over time.
• ⚙️ Simplifies the Docker image by removing redundant installation steps for Python 3.9, as the version included with Ubuntu 20.04 is sufficient.
• 👍 Improves the maintainability of the Dockerfile by using default python aliases, which reduces confusion and potential errors.
• 💨 May result in faster build times and reduced complexity for users setting up the YOLOv5 environment on CPU-based systems.