Exploring Docker Container'S File System

Exploring Docker container's file system

Here are a couple different methods...

A) Use docker exec (easiest)

Docker version 1.3 or newer supports the command exec that behave similar to nsenter. This command can run new process in already running container (container must have PID 1 process running already). You can run /bin/bash to explore container state:

docker exec -t -i mycontainer /bin/bash

see Docker command line documentation

B) Use Snapshotting

You can evaluate container filesystem this way:

# find ID of your running container:
docker ps

# create image (snapshot) from container filesystem
docker commit 12345678904b5 mysnapshot

# explore this filesystem using bash (for example)
docker run -t -i mysnapshot /bin/bash

This way, you can evaluate filesystem of the running container in the precise time moment. Container is still running, no future changes are included.

You can later delete snapshot using (filesystem of the running container is not affected!):

docker rmi mysnapshot

C) Use ssh

If you need continuous access, you can install sshd to your container and run the sshd daemon:

 docker run -d -p 22 mysnapshot /usr/sbin/sshd -D
 
 # you need to find out which port to connect:
 docker ps

This way, you can run your app using ssh (connect and execute what you want).

D) Use nsenter

Use nsenter, see Why you don't need to run SSHd in your Docker containers

The short version is: with nsenter, you can get a shell into an
existing container, even if that container doesn’t run SSH or any kind
of special-purpose daemon

Exploring Docker container's file system

Here are a couple different methods...

A) Use docker exec (easiest)

Docker version 1.3 or newer supports the command exec that behave similar to nsenter. This command can run new process in already running container (container must have PID 1 process running already). You can run /bin/bash to explore container state:

docker exec -t -i mycontainer /bin/bash

see Docker command line documentation

B) Use Snapshotting

You can evaluate container filesystem this way:

# find ID of your running container:
docker ps

# create image (snapshot) from container filesystem
docker commit 12345678904b5 mysnapshot

# explore this filesystem using bash (for example)
docker run -t -i mysnapshot /bin/bash

This way, you can evaluate filesystem of the running container in the precise time moment. Container is still running, no future changes are included.

You can later delete snapshot using (filesystem of the running container is not affected!):

docker rmi mysnapshot

C) Use ssh

If you need continuous access, you can install sshd to your container and run the sshd daemon:

 docker run -d -p 22 mysnapshot /usr/sbin/sshd -D
 
 # you need to find out which port to connect:
 docker ps

This way, you can run your app using ssh (connect and execute what you want).

D) Use nsenter

Use nsenter, see Why you don't need to run SSHd in your Docker containers

The short version is: with nsenter, you can get a shell into an
existing container, even if that container doesn’t run SSH or any kind
of special-purpose daemon

How to access docker's container file system

The docker export command is what you are after. It will print on the standard output the content of a container filesystem as a tar archive.

docker export <container_name> > my_container.tar

or

docker export --output="my_container.tar" <container_name>

How to see docker image contents

You can just run an interactive shell container using that image and explore whatever content that image has.

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 build, 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.

Docker container file system access

You could mount a volume on the container, so the "locally" generated docker files can be accessed from the host. For example:

docker run -v host_dir:container_dir yourDocker (...)

Your docker's process will save the files to his local container_dir, and you could access them via your host's host_dir.

How to view files inside docker image without running it?

Answering my own question.

you can add something like to override the entry point in the Dockerfile and run ls or cat command to see inside.

ENTRYPOINT ls /etc/fluentd

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