Container states (created, running, paused, stopped) in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the created state mean for a Docker container?

The container has been set up but is not running yet. It is ready to start but no processes inside it are active.

beginner

Describe the running state of a Docker container.

The container is active and executing its main process. It is fully operational and can respond to commands or requests.

intermediate

What happens when a Docker container is in the paused state?

The container's processes are temporarily frozen. It uses minimal resources but can be resumed later without restarting.

beginner

Explain the stopped state of a Docker container.

The container has finished running or was manually stopped. Its processes are not running, but the container still exists and can be restarted.

beginner

How can you check the current state of all Docker containers?

Use the command docker ps -a. It lists all containers with their current states like running, exited (stopped), or created.

Which Docker container state means the container is ready but not yet running?

A created

B running

C paused

D stopped

The 'created' state means the container is set up but not running yet.

What does the 'paused' state do to a Docker container?

A Stops and removes the container

B Restarts the container

C Freezes the container's processes temporarily

D Starts the container

Pausing freezes the container's processes without stopping it completely.

Which command shows all Docker containers and their states?

A docker ps

B docker start

C docker stop

D docker ps -a

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

If a container is 'stopped', what does it mean?

A It has finished or was manually stopped

B It is paused temporarily

C It is running normally

D It is being created

A stopped container is not running but still exists and can be restarted.

Which state indicates a container is actively running its main process?

A created

B running

C paused

D stopped

The 'running' state means the container is active and executing.

Explain the differences between the Docker container states: created, running, paused, and stopped.

Think about what the container is doing or not doing in each state.

How can you manage and check the state of Docker containers using commands?

Focus on commands that change or show container states.

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