Common container startup failures in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Identify the error from Docker container startup logs

You run a Docker container but it immediately stops. You check the logs with docker logs container_id and see this message:

standard_init_linux.go:228: exec user process caused: no such file or directory

What is the most likely cause of this error?

A The command specified as ENTRYPOINT or CMD does not exist inside the container.

B The container ran out of memory during startup.

C The Docker daemon is not running on the host machine.

D The container image is corrupted and cannot be loaded.

💡 Hint

Think about what the error means about the process Docker tries to start.

This error means Docker tried to run a command that is missing inside the container. It usually happens if the ENTRYPOINT or CMD points to a file that is not present or has wrong path.

💻 Command Output

intermediate

Diagnose container exit code after startup failure

You start a container and it exits immediately. Running docker ps -a shows the container exited with code 137.

What does exit code 137 usually indicate?

A The container failed due to a syntax error in the Dockerfile.

B The container was killed because it ran out of memory (OOM).

C The container completed successfully and exited normally.

D The container was stopped manually by the user.

💡 Hint

Exit code 137 is 128 + 9, where 9 is the SIGKILL signal.

Exit code 137 means the container process was killed by signal 9 (SIGKILL), often caused by the system killing it due to out-of-memory conditions.

❓ Troubleshoot

advanced

Resolve Docker container failing due to port binding error

You try to start a container with docker run -p 80:80 myapp but get this error:

Bind for 0.0.0.0:80 failed: port is already allocated

What is the best way to fix this issue?

A Restart the Docker daemon to clear port bindings.

B Rebuild the container image to use a different internal port.

C Stop the process currently using port 80 on the host or use a different host port for the container.

D Increase the container's memory limit to allow port binding.

💡 Hint

Port conflicts happen when two processes want the same port on the host.

Port 80 on the host is already in use by another process. You must free that port or map the container port to a different host port.

✅ Best Practice

advanced

Prevent container startup failure due to missing environment variables

Your containerized app requires environment variables to start properly. Sometimes the container fails immediately with configuration errors.

Which practice helps avoid startup failures caused by missing environment variables?

A Use Docker Compose or Kubernetes manifests to define required environment variables explicitly.

B Start the container without environment variables and set them later inside the container.

C Ignore environment variables and rely on default app settings only.

D Hardcode environment variables inside the container image during build.

💡 Hint

Think about how to ensure environment variables are always set before container starts.

Defining environment variables explicitly in deployment files ensures they are always provided when the container starts, preventing configuration errors.

🔀 Workflow

expert

Order the steps to debug a container that fails immediately after starting

You have a container that starts and then stops immediately. Put the following debugging steps in the correct order to find the root cause:

A 3,1,4,2

B 1,4,3,2

C 1,3,4,2

D 4,1,3,2

💡 Hint

Start with quick info about exit code, then logs, then config, then interactive inspection.

First check exit code to understand failure type, then logs for error messages, then Dockerfile for config issues, finally run interactively to explore environment.