Debugging volume mount issues in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a common cause of volume mount failures in Docker?

A common cause is incorrect file or directory paths on the host system that do not exist or have wrong permissions.

beginner

How can you check if a volume is correctly mounted inside a running Docker container?

Use docker exec -it <container_name> ls <mount_path> to list files inside the mounted directory.

intermediate

Why might a Docker volume mount show empty inside the container even though the host directory has files?

This can happen if the container path is overwritten by another Docker volume or if the mount path is incorrect.

intermediate

What Docker command option helps you see detailed error messages when starting containers with volume mounts?

Use docker run --rm -it -v <host_path>:<container_path> <image> and check the error output for permission or path issues.

intermediate

How do file permissions affect Docker volume mounts?

If the host directory or files have restrictive permissions, the container user may not access them, causing mount issues.

What command lets you inspect the contents of a mounted volume inside a running Docker container?

A docker exec -it <container> ls <mount_path>

B docker volume ls

C docker ps

D docker inspect <container>

Use 'docker exec' to run commands inside the container and check the mounted directory contents.

If a volume mount shows empty inside the container, what is a likely cause?

A The container is not running

B Docker daemon is stopped

C The image is corrupted

D The container path is overwritten by another volume

An existing volume or mount can overwrite the path, hiding the host files.

Which of these can cause permission denied errors on volume mounts?

A Dockerfile missing CMD

B Container image is too large

C Host directory has restrictive permissions

D Network issues

If the host directory permissions do not allow container access, mounts fail.

What is the correct syntax to mount a host directory to a container path in Docker run?

A docker run -v /host/path:/container/path image

B docker run -v /container/path:/host/path image

C docker run --mount /container/path:/host/path image

D docker run --volume image /host/path:/container/path

The syntax is host path first, then container path separated by a colon.

How can you verify if a host directory exists before mounting it in Docker?

A Use docker volume ls

B Use ls /host/path on the host machine

C Run docker ps

D Restart Docker daemon

Checking the directory on the host ensures the path exists for mounting.

Explain the steps you would take to debug a Docker volume mount that appears empty inside the container.

Think about verifying paths, permissions, and container inspection.

Describe how file permissions on the host affect Docker volume mounts and how to fix permission issues.

Focus on permission settings and user access.