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Detect image size

Docker Disk Usage – How to Find Out What’s Taking Space

If your Docker data directory is taking up unexpected space (e.g. 1.7 TB), here’s how you can quickly check what's using it.

🔍 1. Show Docker Image Sizes

List all Docker images with their size:

docker images --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"

📊 2. Summary of Space Usage

Get a high-level overview of space used by:

  • Images
  • Containers
  • Volumes
  • Build cache
docker system df

🧱 3. Check Disk Usage in Overlay2 (or similar)

If Docker uses overlay2 (default), check which directories use most space:

du -h --max-depth=1 /mnt/toshiba_drive/docker-data/overlay2 | sort -hr | head -n 20

Replace /mnt/toshiba_drive/docker-data with your actual Docker data root if different.

🧹 4. Clean Up Unused Data

To safely clean up all unused containers, images, volumes, and caches:

docker system prune -a --volumes

⚠️ WARNING: This will delete all unused resources. Useful for reclaiming space.

🔍 5. Preview Before Cleanup

To see details before removing anything:

docker system df -v

This will show which images, containers, and volumes are taking space and whether they’re in use.

✅ Tip

After cleanup, run docker system df again to compare space usage before/after.