Removing containers in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command is used to remove a single Docker container?

The command docker rm <container_id_or_name> removes a single stopped Docker container.

beginner

How do you remove all stopped Docker containers at once?

Use docker container prune to remove all stopped containers in one command.

intermediate

What option allows you to force remove a running Docker container?

The -f or --force option with docker rm forces removal of a running container by stopping it first.

beginner

What happens if you try to remove a running container without the force option?

Docker will return an error saying the container is running and cannot be removed unless you stop it or use the force option.

intermediate

How can you remove multiple containers at once using their IDs or names?

You can list multiple container IDs or names separated by spaces after docker rm, like docker rm container1 container2.

Which command removes all stopped Docker containers?

A docker rm --all

B docker rm -f all

C docker stop all

D docker container prune

The docker container prune command removes all stopped containers safely.

What does the -f option do with docker rm?

A Filters containers by name

B Forces removal of a running container

C Formats output

D Finds containers by ID

The -f option forces Docker to stop and remove a running container.

What happens if you try to remove a running container without -f?

A Docker returns an error

B Container is removed immediately

C Container is paused

D Container is renamed

Docker will not remove a running container without the force option and will show an error.

How do you remove multiple containers at once?

A docker rm container1 container2

B docker rm -all

C docker stop container1 container2

D docker rm --batch

You list multiple container names or IDs separated by spaces after docker rm.

Which command removes a single stopped container named 'webapp'?

A docker rm -f webapp

B docker stop webapp

C docker rm webapp

D docker container prune webapp

Use docker rm webapp to remove a stopped container named 'webapp'.

Explain how to safely remove Docker containers that are no longer needed.

Think about stopping containers and batch removal commands.

Describe what happens if you try to remove a running container without forcing it.

Consider Docker's safety checks before removal.

Practice

1. What does the docker rm command do?

easy

A. Lists all containers

B. Stops running containers

C. Deletes one or more stopped containers

D. Creates a new container

Solution

1. Step 1: Understand the purpose of docker rm

   The docker rm command is used to remove containers from the system.

2. Step 2: Check container state requirement

   Containers must be stopped before removal unless forced. So, docker rm deletes stopped containers.

3. Final Answer:

   Deletes one or more stopped containers -> Option C

4. Quick Check:

   docker rm = Delete stopped containers [OK]

Hint: Remember: rm means remove stopped containers only [OK]

Common Mistakes:

• Thinking it stops containers
• Confusing with container creation
• Assuming it lists containers

2. Which of the following is the correct syntax to force remove a running container named webapp?

easy

A. docker rm -f webapp

B. docker rm --force webapp

C. docker rm webapp -f

D. docker rm webapp --force

Solution

1. Step 1: Identify the correct flag position

   The force flag -f must come before the container name in the command.

2. Step 2: Verify correct syntax

   The correct syntax is docker rm -f webapp. Other placements cause errors or are invalid.

3. Final Answer:

   docker rm -f webapp -> Option A

4. Quick Check:

   Force flag before name = correct syntax [OK]

Hint: Put flags before container names in docker commands [OK]

Common Mistakes:

• Placing flags after container names
• Using long flag incorrectly
• Omitting the force flag for running containers

3. Given these commands run in order:

docker run -d --name test1 nginx
docker run -d --name test2 nginx
docker stop test1
docker rm test1 test2

What will happen?

medium

A. Only test2 is removed; test1 removal fails

B. Both containers test1 and test2 are removed

C. Neither container is removed

D. Only test1 is removed; test2 removal fails

Solution

1. Step 1: Analyze container states before removal

   test1 is stopped before removal, test2 is still running.

2. Step 2: Understand docker rm behavior

   docker rm removes stopped containers only. It will remove test1 but fail on running test2.

3. Final Answer:

   Only test1 is removed; test2 removal fails -> Option D

4. Quick Check:

   Stopped containers removed; running containers not [OK]

Hint: Only stopped containers get removed without -f flag [OK]

Common Mistakes:

• Assuming running containers get removed without force
• Thinking both containers are stopped
• Ignoring the stop command effect

4. You run docker rm mycontainer but get an error: Error response from daemon: You cannot remove a running container. What is the best fix?

medium

A. Use docker rm -v mycontainer to remove volumes

B. Stop the container first using docker stop mycontainer

C. Restart Docker daemon and try again

D. Rename the container and remove it

Solution

1. Step 1: Understand the error cause

   The error says the container is running and cannot be removed directly.

2. Step 2: Apply correct fix

   Stopping the container first with docker stop mycontainer allows safe removal.

3. Final Answer:

   Stop the container first using docker stop mycontainer -> Option B

4. Quick Check:

   Stop container before removal = correct fix [OK]

Hint: Stop running containers before removing them [OK]

Common Mistakes:

• Trying to remove running container without stopping
• Using volume removal flag incorrectly
• Restarting Docker unnecessarily

5. You want to clean up all stopped containers at once. Which command achieves this safely and efficiently?

hard

A. docker rm $(docker ps -a -q -f status=exited)

B. docker rm -f $(docker ps -q)

C. docker stop $(docker ps -q) && docker rm $(docker ps -q)

D. docker rm $(docker ps -q -f status=running)

Solution

1. Step 1: Identify stopped containers

   The filter -f status=exited lists only stopped containers.

2. Step 2: Remove only stopped containers safely

   Using docker rm $(docker ps -a -q -f status=exited) removes all stopped containers without affecting running ones.

3. Final Answer:

   docker rm $(docker ps -a -q -f status=exited) -> Option A

4. Quick Check:

   Remove stopped containers only = docker rm $(docker ps -a -q -f status=exited) [OK]

Hint: Use filter exited to remove only stopped containers [OK]

Common Mistakes:

• Removing running containers forcibly without need
• Stopping and removing all containers blindly
• Using wrong filters causing errors