Container states (created, running, paused, stopped) in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Identify the container state after creation

You run the command docker create nginx. What is the state of the container immediately after this command?

A created

B running

C paused

D stopped

💡 Hint

Creating a container sets it up but does not start it.

The docker create command sets up a container but does not start it. So the container state is created.

💻 Command Output

intermediate

State of container after running and pausing

You start a container with docker run -d nginx and then pause it with docker pause [container_id]. What is the container's state after pausing?

A running

B created

C stopped

D paused

💡 Hint

Pausing suspends the container's processes temporarily.

After pausing, the container is in the paused state, meaning its processes are suspended but the container is still allocated.

✅ Best Practice

advanced

Choosing the correct command to stop a running container

Which command properly stops a running Docker container and changes its state to 'stopped'?

A docker stop [container_id]

B docker pause [container_id]

C docker kill [container_id]

D docker rm [container_id]

💡 Hint

Stopping allows graceful shutdown, killing is forceful.

docker stop sends a signal to gracefully stop the container, changing its state to stopped. docker kill forcefully terminates it, but the state is still considered stopped. docker pause only suspends the container. docker rm removes the container.

❓ Troubleshoot

advanced

Diagnosing why a container is stuck in 'paused' state

You notice a container is stuck in the 'paused' state and does not resume with docker unpause. What is a likely cause?

A The container was removed while paused

B Docker daemon crashed and did not restore container state

C The container is in 'created' state, not 'paused'

D The container was never started

💡 Hint

Docker daemon manages container states and may lose track after a crash.

If the Docker daemon crashes while a container is paused, it may fail to restore the paused state properly, causing the container to be stuck. The container cannot resume until the daemon is restarted or the container is manually handled.

🧠 Conceptual

expert

Understanding container lifecycle transitions

Which sequence correctly represents the lifecycle states of a Docker container from creation to removal?

A created → paused → running → stopped → removed

B running → created → paused → stopped → removed

C created → running → paused → running → stopped → removed

D created → running → stopped → paused → removed

💡 Hint

Think about the order in which a container can be paused and resumed.

The container lifecycle starts with created, then running when started. It can be paused and then resumed back to running. After stopping, it moves to stopped before removal.

Practice

1. Which Docker container state means the container is currently executing processes?

easy

A. stopped

B. created

C. paused

D. running

Solution

1. Step 1: Understand container states

   The 'running' state means the container is actively executing its processes.

2. Step 2: Compare other states

   'Created' means container is made but not started, 'paused' means temporarily halted, 'stopped' means container is not running.

3. Final Answer:

   running -> Option D

4. Quick Check:

   Active container = running [OK]

Hint: Running means container is actively working [OK]

Common Mistakes:

• Confusing 'created' with 'running'
• Thinking 'paused' means running
• Mixing 'stopped' with 'running'

2. Which command shows all Docker containers including stopped ones?

easy

A. docker ps -a

B. docker pause

C. docker start

D. docker ps

Solution

1. Step 1: Recall docker ps usage

   'docker ps' shows only running containers by default.

2. Step 2: Use option to show all containers

   'docker ps -a' lists all containers, including stopped and paused ones.

3. Final Answer:

   docker ps -a -> Option A

4. Quick Check:

   Show all containers = docker ps -a [OK]

Hint: Add -a to see all containers, not just running [OK]

Common Mistakes:

• Using 'docker ps' alone shows only running containers
• Confusing 'docker start' with listing containers
• Thinking 'docker pause' lists containers

3. What is the state of the container after running these commands?

docker create nginx
docker start <container_id>
docker pause <container_id>

medium

A. paused

B. created

C. running

D. stopped

Solution

1. Step 1: Analyze commands sequence

   'docker create' makes container in 'created' state, 'docker start' moves it to 'running'.

2. Step 2: Effect of 'docker pause'

   'docker pause' suspends container processes without stopping it, changing state to 'paused'.

3. Final Answer:

   paused -> Option A

4. Quick Check:

   Pause command sets state to paused [OK]

Hint: Pause command changes running to paused state [OK]

Common Mistakes:

• Assuming container stays running after pause
• Confusing created with paused
• Thinking pause stops the container

4. You ran docker pause mycontainer but got an error saying container is not running. What is the likely cause?

medium

A. Container is already paused

B. Container is stopped or not started

C. Container name is incorrect

D. Docker daemon is not running

Solution

1. Step 1: Understand pause command requirements

   'docker pause' only works on running containers to suspend them temporarily.

2. Step 2: Interpret error message

   Error about container not running means it is stopped or never started, so pause cannot apply.

3. Final Answer:

   Container is stopped or not started -> Option B

4. Quick Check:

   Pause needs running container [OK]

Hint: Pause only works on running containers [OK]

Common Mistakes:

• Trying to pause stopped containers
• Ignoring container state before pausing
• Assuming pause works on any container

5. You want to temporarily stop a container without losing its state and then resume it later. Which sequence of commands should you use?

hard

A. docker kill <container_id> then docker start <container_id>

B. docker stop <container_id> then docker start <container_id>

C. docker pause <container_id> then docker unpause <container_id>

D. docker restart <container_id> then docker pause <container_id>

Solution

1. Step 1: Understand stopping vs pausing

   'docker stop' stops container and loses running state; 'docker pause' suspends without stopping.

2. Step 2: Identify commands to pause and resume

   'docker pause' suspends container, 'docker unpause' resumes it preserving state.

3. Final Answer:

   docker pause & docker unpause -> Option C

4. Quick Check:

   Pause/unpause = temporary stop and resume [OK]

Hint: Pause to stop temporarily, unpause to resume [OK]

Common Mistakes:

• Using stop loses container state
• Confusing kill with pause
• Restarting instead of unpausing