Linux+ Container Operations with Docker Questions and Answers

Question 1

A Linux administrator is performing maintenance on a Docker host and needs to reclaim disk space. Which command should they use to remove all unused images, including tagged images that are not associated with any container?

Accepted Answer

docker image prune -a

Answer

The `docker image prune` command is used to remove unused images. By default, it only removes dangling images (those without a tag). The `-a` (or `--all`) flag extends this to remove all images that are not associated with at least one container, which is what the scenario requires.

Question 2

Which of the following commands will start a new container from the `ubuntu:latest` image, name it `my-test-container`, and ensure it runs in the background as a daemon?

Accepted Answer

docker run -d --name my-test-container ubuntu:latest

Answer

The `docker run` command creates and starts a new container. The `-d` flag runs the container in detached mode (in the background), and the `--name` flag assigns a user-friendly name to it.

Question 3

A developer needs to deploy a database in a Docker container. It is critical that the database's data persists even if the container is removed. Which command correctly maps a Docker-managed named volume called `db_data` to the `/var/lib/mysql` directory inside the container?

Accepted Answer

docker run -d --mount type=volume,source=db_data,target=/var/lib/mysql mysql

Answer

To persist data using a Docker-managed named volume, the `--mount` flag is recommended for its clarity. The syntax `type=volume,source=db_data,target=/var/lib/mysql` explicitly creates (if not existing) a named volume called `db_data` and maps it to the `/var/lib/mysql` directory inside the container. This ensures data persists independently of the container's lifecycle.

Question 4

An administrator is troubleshooting a network connectivity issue with a running container named `api-gateway`. Which command would they use to view detailed configuration information about the container, including its assigned IP address, mounts, and port mappings?

Accepted Answer

docker inspect api-gateway

Answer

The `docker inspect` command provides low-level, detailed information on Docker objects. When run against a container, it returns a JSON array containing its complete configuration, including network settings like the IP address, volume mounts, and environment variables.

Question 5

A developer has created a web application that listens on port 3000 inside its container. To make this application accessible on port 80 on the host machine, which `docker run` flag and argument should be used?

Accepted Answer

-p 80:3000

Answer

The `-p` or `--publish` flag is used to map a host port to a container port. The format is `HOST_PORT:CONTAINER_PORT`. Therefore, to map port 80 on the host to port 3000 inside the container, the correct syntax is `-p 80:3000`.

Linux Practice Test

Linux Practice Test

Linux+ Container Operations with Docker Questions and Answers