Docker Docker Troubleshooting Debugging Container Start Failures docker run entrypoint docker commit docker diff

1. Core Command / Concept

Debugging container start failures by identifying and fixing issues with container configuration, images, and environment. docker run -it --rm

2. Step-by-Step

1. Check the container logs for errors: docker logs -f <container_name>
   Output: container logs with error messages.
   Clean up: stop the container with docker stop <container_name>.

2. Check the container configuration: docker inspect <container_name>
   Output: container configuration details.
   Clean up: none.

3. Check the image configuration: docker images
   Output: list of available images.
   Clean up: none.

4. Check the environment variables: docker run -it --rm -e <env_var> <image_name>
   Output: environment variable value.
   Clean up: stop the container with docker stop <container_name>.

5. Check the entrypoint: docker run -it --rm --entrypoint <entrypoint> <image_name>
   Output: container logs with error messages.
   Clean up: stop the container with docker stop <container_name>.

6. ⚠️ Delete all stopped containers: docker system prune -f
   Output: confirmation message.
   Clean up: none.

3. Real Commands with Examples

Example 1: Debugging container start failure due to missing environment variable

Purpose: Set environment variable for container.
Command: docker run -it --rm -e MY_VAR=hello world Flags: -e MY_VAR=hello sets environment variable MY_VAR to hello, and world is the image name.

Example 2: Debugging container start failure due to incorrect entrypoint

Purpose: Set entrypoint for container.
Command: docker run -it --rm --entrypoint /bin/bash my_image Flags: --entrypoint /bin/bash sets the entrypoint to /bin/bash, and my_image is the image name.

Example 3: Debugging container start failure due to missing image

Purpose: Pull and run the image.
Command: docker pull my_image && docker run -it --rm my_image Flags: docker pull my_image pulls the image, and docker run -it --rm my_image runs the image.

4. Common Errors

Error 1: "Error: container failed to start"

Why it happens: missing environment variable or incorrect entrypoint.
One-line fix: docker run -it --rm -e MY_VAR=hello world

Error 2: "Error: image not found"

Why it happens: missing image or incorrect image name.
One-line fix: docker pull my_image && docker run -it --rm my_image

Error 3: "Error: container failed to start due to permission issues"

Why it happens: incorrect permissions for container.
One-line fix: docker run -it --rm -u 0 my_image

5. Quick Checks

Scenario 1: Container logs show error messages

Situation: container failed to start.
Command to run: docker logs -f <container_name> Correct response: container logs with error messages.

Scenario 2: Container configuration shows incorrect settings

Situation: container failed to start.
Command to run: docker inspect <container_name> Correct response: container configuration details with incorrect settings.

Scenario 3: Image configuration shows missing image

Situation: container failed to start.
Command to run: docker images Correct response: list of available images with missing image.

6. Last-Minute Reference

• docker run flags: -it --rm -e --entrypoint • docker inspect flags: --format • docker images flags: --all • docker logs flags: -f --tail • docker stop flags: --time • docker system prune flags: -f --volumes • ⚠️ docker system prune deletes all stopped containers.
• ⚠️ docker stop with --time flag can take up to 10 seconds to stop the container.
• ⚠️ docker run with --rm flag deletes the container when it stops.
• ⚠️ docker inspect shows container configuration details.
• ⚠️ docker images shows list of available images.
• ⚠️ docker logs shows container logs.
• ⚠️ docker stop stops the container.