Resolving the no such file or directory Error When Starting Docker Containers

Описание: Discover why your Docker container runs successfully without a volume but fails with an error. Learn how to fix the `no such file or directory` issue while using volumes in Docker.
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This video is based on the question https://stackoverflow.com/q/68338463/ asked by the user 'Vazid' ( https://stackoverflow.com/u/8665479/ ) and on the answer https://stackoverflow.com/a/68338613/ provided by the user 'BMitch' ( https://stackoverflow.com/u/596285/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Docker's Volume Mounting and Common Errors

Docker containers provide a powerful way to package applications in a lightweight manner, but sometimes they can be tricky to debug, especially when it comes to mounting volumes. One common issue users encounter is the error message: no such file or directory. Today, we'll explore this problem and provide a detailed solution.

The Problem: An Error When Starting the Docker Container

Imagine you've created a Docker image using a specific Dockerfile. Your Dockerfile looks something like this:

[[See Video to Reveal this Text or Code Snippet]]

When you run the image without the -v option (volume mount), it works perfectly:

[[See Video to Reveal this Text or Code Snippet]]

However, when you attempt to mount a volume like this:

[[See Video to Reveal this Text or Code Snippet]]

You receive the following error:

[[See Video to Reveal this Text or Code Snippet]]

This can be misleading since you can see that the Entrypoint.sh file is present in the image.

The Solution: Understanding Volume Mounting Behavior

The key to solving this issue lies in understanding how Docker handles volume mounting, which follows the general principles of filesystem mounting in Linux. When you mount a host directory onto a directory in the container, here's what happens:

Overlaying Content: When you mount a volume on top of a directory, the contents of that directory within the image are hidden as long as the mount is active. Hence, when you try to access /docker/crawler/docker/Entrypoint.sh, it appears missing because the host's /docker directory is obscuring the image's contents. Essentially, you're not merging the contents of both — you only see what is in the mounted volume.

Key Takeaways:

No Visibility of Image Contents: When a volume is mounted, its contents overshadow the image contents of the same directory.

Named Volume Caveat: If you use a named volume mount, it initializes with the contents of the image when first created, but subsequent alterations do not sync back with the image.

Best Practices to Avoid This Error

To prevent similar issues, consider these best practices:

Separate Application and Data: Keep application binaries/scripts within your Docker image and data in separate folders.

Mounting and Initialization: When using named volumes, ensure the volume is indeed empty/new before first use so that it can retrieve initial contents from the image.

By following these guidelines and understanding the implications of volume mounts, you can manage and run your Docker containers more effectively, without encountering misleading errors like no such file or directory.

If you encounter a similar situation again, remember: check the mounting behavior, and be mindful of what is being obscured in the underlying image. Happy Dockerizing!