Linux+ Container Operations with Docker Flashcards

A container is running but needs to be stopped gracefully. Which signal does docker stop send by default before force-killing the process?

Answer: SIGTERM

docker stop sends SIGTERM first, giving the process time to shut down cleanly, then sends SIGKILL after a timeout (default 10 seconds).

Which Dockerfile instruction is used to define the default working directory for subsequent RUN, CMD, ENTRYPOINT, COPY, and ADD instructions?

Answer: WORKDIR

WORKDIR sets the working directory inside the container image and creates it if it does not exist.

What does the --read-only flag do when passed to docker run?

Answer: Makes the container's root filesystem read-only, preventing writes

The --read-only flag mounts the container's root filesystem as read-only, improving security by preventing unauthorized file modifications.

A Linux administrator wants containers on two different Docker hosts to communicate. Which network driver should be used?

Answer: overlay

Overlay networks span multiple Docker hosts using VXLAN encapsulation and require a key-value store like etcd or Consul for coordination.

What happens to container data stored in a named volume when the container is deleted with docker rm?

Answer: The volume persists and must be removed separately with docker volume rm

Named volumes have an independent lifecycle from containers; deleting a container does not remove its associated named volumes.

Which command shows the layer history and build commands used to create a Docker image?

Answer: docker history

docker history displays each layer of an image, its size, and the instruction that created it.

When using docker run -p 8080:80, what does port 8080 represent?

Answer: The host machine's port that maps to the container

In -p host_port:container_port format, 8080 is the host port that forwards traffic to port 80 inside the container.