Copying files to and from containers in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Copying a file from host to container

You run the command docker cp ./app/config.yaml mycontainer:/app/config.yaml. What is the expected result?

A The command fails because the container name must be specified with a leading slash.

B The command copies the entire app directory from the host to the container.

C The file config.yaml is copied from the container's /app directory to the host's current directory.

D The file config.yaml is copied from the host's current directory to /app inside the container named mycontainer.

💡 Hint

Remember the syntax is docker cp source_path container:destination_path to copy files into a container.

The docker cp command copies files between host and container. When the source is a host path and the destination is container:path, it copies from host to container.

💻 Command Output

intermediate

Copying a directory from container to host

What happens when you run docker cp mycontainer:/var/logs ./logs_backup?

A The entire /var/logs directory from the container is copied to a new directory logs_backup on the host.

B Only the files inside /var/logs are copied, but not the directory itself.

C The command fails because the destination path on the host must be absolute.

D The command copies the /var/logs directory from the host to the container.

💡 Hint

Check if the source is container:path and destination is host path.

When copying from container to host, docker cp copies the directory or file preserving structure at the destination path.

❓ Troubleshoot

advanced

Why does this docker cp command fail?

You run docker cp /home/user/data.txt mycontainer:/data/ but get an error: Error: No such container:path: mycontainer:/data/. What is the most likely cause?

A The docker cp command cannot copy files into directories inside containers.

B The source file /home/user/data.txt does not exist on the host.

C The container named mycontainer is not running or does not exist.

D The destination path inside the container must not end with a slash.

💡 Hint

Check if the container name is correct and the container is running.

The error indicates docker cannot find the container or the path inside it. Usually the container name is wrong or container is stopped.

✅ Best Practice

advanced

Best practice for copying large files into containers

Which approach is best when you need to copy a large file repeatedly into a container during development?

A Mount the host directory containing the file as a volume inside the container.

B Use docker cp every time you need to copy the file.

C Rebuild the container image with the file included each time.

D Use scp to copy the file into the container's IP address.

💡 Hint

Think about avoiding repeated copying and making changes instantly visible.

Mounting a host directory as a volume allows instant file changes without copying repeatedly.

🔀 Workflow

expert

Order the steps to copy a file from host to a running container and verify it

Arrange these steps in the correct order to copy a file named settings.json from the host to a running container named webapp and verify the copy.

A 1,4,2,3

B 4,1,2,3

C 4,2,1,3

D 2,4,1,3

💡 Hint

You must confirm the container is running before copying files.

First check container is running, then copy file, then open shell, then verify file inside container.