Module 13 Lesson 1: Common Docker Errors

Every Docker user will eventually face these errors. Knowing how to read them will save you hours of Googling.

1. "Cannot connect to the Docker daemon"

• Meaning: The Docker Client (the CLI) cannot talk to the Docker Server (the engine).
• Fix:
  • Windows/Mac: Is Docker Desktop actually OPEN?
  • Linux: Is the service running? sudo systemctl start docker.
  • Permissions: Did you forget to add your user to the docker group? (Review Module 2).

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2. "Bind for 0.0.0.0:80 failed: port is already allocated"

• Meaning: You are trying to use a port (e.g., 80) that is already being used by another app or another container.
• Fix:
  • Find the culprit: lsof -i :80 (Mac/Linux) or netstat -ano | findstr :80 (Windows).
  • Either stop the other app or change your Docker port: -p 8080:80.

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3. "No space left on device"

• Meaning: Your computer's hard drive (or the virtual drive Docker uses) is full.
• Fix:
  • The Nuke: docker system prune -a --volumes.
  • The Precise Way: Use docker image ls and docker volume ls to find the 10GB images you haven't used in months.

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4. "manifest for image:tag not found"

• Meaning: You tried to pull an image that doesn't exist on the registry or has a typo in the name/tag.
• Fix:
  • Check for typos (e.g., nginix vs nginx).
  • Search Docker Hub to verify the tag exists (e.g., 3.9-alpine might be 3.9.18-alpine).

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5. "Exec format error" (The M1/M2/M3 special)

• Meaning: You are trying to run an image built for one architecture (ARM64) on a different architecture (AMD64).
• Fix:
  • Use docker buildx to build "Multi-Platform" images.
  • Switch to a base image that supports your processor.

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Exercise: The Error Hunter

1. Try to run docker run -p 8080:80 nginx two times in two different terminals. What error does the second one give?
2. Stop the Docker Desktop app on your machine. Now try to run docker ps. What is the error?
3. Type docker pull ubuntu:99.9. What error do you get?
4. Why is "Reading the first three words" of an error message usually enough to solve it?

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Summary

In Docker, errors are rarely "Magic." They are almost always about Permissions, Ports, or Paths. By treating every error as a logical puzzle, you stop being afraid of the red text and start becoming a master of the engine.

Next Lesson: Checking the vitals: Analyzing container performance.