Container states (created, running, paused, stopped) in Docker - Commands & Configuration

Introduction

Containers are like small packages that hold your app and everything it needs. They can be in different states like created, running, paused, or stopped, which tells you what the container is doing right now.

When you want to start an app inside a container and check if it is running properly

When you need to pause a container temporarily without stopping it completely

When you want to stop a container to save resources but keep its data intact

When you create a container but want to start it later

When you want to see the current status of your containers to manage them

Commands

This command creates a container named 'example-container' from the nginx image but does not start it yet. It is in the 'created' state.

Terminal

docker create --name example-container nginx

Expected Output

a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x4y5z6

→

--name - Assigns a custom name to the container for easy reference

This command starts the container named 'example-container', changing its state from 'created' to 'running'.

Terminal

docker start example-container

Expected Output

example-container

This command pauses the running container, freezing its processes temporarily without stopping it.

Terminal

docker pause example-container

Expected Output

No output (command runs silently)

This command resumes a paused container, returning it to the 'running' state.

Terminal

docker unpause example-container

Expected Output

No output (command runs silently)

This command stops the running container, changing its state to 'exited'. The container is not removed and can be started again.

Terminal

docker stop example-container

Expected Output

example-container

This command lists all containers including stopped ones, filtering by name 'example-container' and showing their current status.

Terminal

docker ps -a --filter "name=example-container" --format "{{.Names}} {{.Status}}"

Expected Output

example-container Exited (0) 5 seconds ago

→

-a - Show all containers, including stopped ones

→

--filter - Filter containers by name

→

--format - Customize the output format

Key Concept

If you remember nothing else from this pattern, remember: container states tell you exactly what your container is doing and help you control its lifecycle.

Common Mistakes

Trying to start a container that is already running

Docker will return an error because the container is already in the running state

Check the container state with 'docker ps' before starting it

Pausing a container that is not running

You can only pause containers that are running; otherwise, Docker will error

Ensure the container is running before pausing it

Stopping a container that is already stopped

Docker will return an error or no effect because the container is not running

Use 'docker ps -a' to check container status before stopping

Summary

Create a container with 'docker create' to prepare it without running.

Start the container with 'docker start' to run your app inside it.

Pause and unpause containers to temporarily freeze and resume processes.

Stop containers with 'docker stop' to end their running state but keep them for later use.

Use 'docker ps -a' with filters to check container states anytime.

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