Docker: How to Extract The Docker Image into Local System

How can I extract the docker filesystem into my local filesystem so I no longer have to use docker

If the image has the tar command available, you can run:

docker run --rm yourimage tar -C / -cf- | tar -C /path/to/root -xf-

This will tar up the contents up the image, and then untar it on your host in the location of your choice (/path/to/root in the above example).

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I once wrote a tool called undocker for extracting a docker image to a local directory; you would use it like this:

docker save myimage | undocker

I haven't used it much in the past several years, but it seems to work on a few test images. This is useful if you're trying to extract the contents of an image in which you can't run tar.

How to copy Docker images from one host to another without using a repository

You will need to save the Docker image as a tar file:

docker save -o <path for generated tar file> <image name>

Then copy your image to a new system with regular file transfer tools such as cp, scp or rsync(preferred for big files). After that you will have to load the image into Docker:

docker load -i <path to image tar file>

PS: You may need to sudo all commands.

EDIT:
You should add filename (not just directory) with -o, for example:

docker save -o c:/myfile.tar centos:16

Docker: Copying files from Docker container to host

In order to copy a file from a container to the host, you can use the command

docker cp <containerId>:/file/path/within/container /host/path/target

Here's an example:

$ sudo docker cp goofy_roentgen:/out_read.jpg .

Here goofy_roentgen is the container name I got from the following command:

$ sudo docker ps

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                                            NAMES
1b4ad9311e93        bamos/openface      "/bin/bash"         33 minutes ago      Up 33 minutes       0.0.0.0:8000->8000/tcp, 0.0.0.0:9000->9000/tcp   goofy_roentgen

You can also use (part of) the Container ID. The following command is equivalent to the first

$ sudo docker cp 1b4a:/out_read.jpg .

How to see docker image contents

If the image contains a shell, you can run an interactive shell container using that image and explore whatever content that image has. If sh is not available, the busybox ash shell might be.

For instance:

docker run -it image_name sh

Or following for images with an entrypoint

docker run -it --entrypoint sh image_name

Or if you want to see how the image was built, meaning the steps in its Dockerfile, you can:

docker image history --no-trunc image_name > image_history

The steps will be logged into the image_history file.

Is it possible to extract the Dockerfile from a docker container

You have docker history <image> that is very helpful. It can even be used to generate a dockerfile if none of the steps involved stdin.

If a step as stdin, the only way to know what happened would be to do docker logs <container id parent>, but if you do not have the container, you can't.

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