Listing containers (docker ps, docker ps -a) - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of docker ps command

You run docker ps on a system with three containers: one running, two stopped. What will docker ps show?

Docker

docker ps

A Lists only the running container with its details

B Lists all three containers with their details

C Lists only the stopped containers

D Shows an error because some containers are stopped

💡 Hint

Remember, docker ps shows only running containers by default.

The docker ps command lists only containers that are currently running. Stopped containers are not shown unless you add the -a option.

💻 Command Output

intermediate

Output of docker ps -a command

You run docker ps -a on a system with two running and two stopped containers. What will the command output include?

Docker

docker ps -a

A Lists only the two running containers

B Lists all four containers with their status

C Lists only the two stopped containers

D Shows an error because of invalid option

💡 Hint

The -a option means 'all' containers.

The docker ps -a command lists all containers, whether running or stopped, showing their status.

❓ Troubleshoot

advanced

Why does docker ps show no containers?

You run docker ps but it shows no containers, even though you know containers exist on the system. What is the most likely reason?

Docker

docker ps

A You need to run <code>docker ps -a</code> to see containers

B You do not have permission to list containers

C Docker daemon is not running

D No containers are currently running

💡 Hint

Think about what docker ps shows by default.

docker ps shows only running containers. If none are running, it will show no containers.

✅ Best Practice

advanced

Best command to list all containers including stopped ones

Which command should you use to see all containers, including those that have stopped?

A docker container ls

B docker ps

C docker ps -a

D docker container ls -q

💡 Hint

The -a option means 'all'.

docker ps -a lists all containers, running or stopped. docker container ls is equivalent to docker ps and shows only running containers. The -q option shows only IDs.

🧠 Conceptual

expert

Understanding container listing filters

You want to list only containers that exited with a non-zero status. Which command will do this?

A docker ps -a --filter "exited=1"

B docker ps -a --filter "exited!=0"

C docker ps -a --filter "exited=0"

D docker ps -a --filter "status=exited"

💡 Hint

The filter 'exited' takes an exit code number.

The --filter "exited=1" option lists containers that exited with status 1 (non-zero). Using exited=0 lists containers that exited successfully. The syntax exited!=0 is invalid. status=exited lists all exited containers regardless of exit code.