How to open docker containers file system

Question

I'm new to docker and I want to know how I can explore docker containers from the inside. Like what files exist inside of it. For Eg. when I download images from the docker index, I don't know what that image contains so it's impossible to start the application.

What should I do? Is there a way to SSH into them?

Answer 1

There are various ways you can do this:

Method 1: Snapshoting

You can go through the container filesystem:

# 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

By doing this you can check the filesystem of running container in that moment in time. The container would still be in running condition with no future changes included.

After, you could delete this snapshot:

docker rmi mysnapshot

Method 2: SSH

If you want something continuous, you can use SSHD. You'll have to install it on your container and then execute 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'll be able to run you application using SSH.

Method 3: docker exec

If bash is present on your container you can directly use shell on your container by using:

docker exec -t -i mycontainer /bin/bash

Check Docker CLI documentation

Answer 2

Adding on to @DareDev's answer there's one more method.

Method 4: Use nsenter

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.

For more info see http://blog.docker.com/2014/06/why-you-dont-need-to-run-sshd-in-docker/