CODEWITHSUNDEEP
docker
Arun Kaushal
Arun Kaushal

Reputation: 631

Detach container from host console

I am creating a docker container with Ubuntu:16.04 image using python docker package. I am passing tty as True and detach as True to the client.containers.run() function. The container starts with /sbin/init process. The container is created successfully. But the problem is, the login prompt on my host machine is replaced with the container login prompt on my host machine console. As a result, I am not able to the login on the machine on the console. SSH connection to the machine work fine.

This happens even when I run my python script after connecting SSH to the machine. I tried different options like setting tty to False, setting stdout to False, setting the environment variable TERM to xterm in the container, but nothing help.

It would be really great if someone can suggest a solution for this problem.

My script is very simple:

import docker
client = docker.from_env()

container = client.containers.run('ubuntu:16.04', '/sbin/init', privileged=True,
       detach=True, tty=True, stdin_open=True, stdout=False, stderr=False,
       environment=['TERM=xterm'])

I am not using any dockerfile.

I have been able to figure out that this problem happens when I start container in privileged mode. If I do this, the /sbin/init process launches /sbin/agetty processes which causes /dev/tty to be attached to the container. I need to figure out a way to start /sbin/init in such a way that it does not create /sbin/agetty processes.

Upvotes: 1

Views: 240

Answers (1)

David Maze
David Maze

Reputation: 159438

/sbin/init in Ubuntu is a service called systemd. If you look at the linked page it does a ton of things – configures various kernel parameters, mounts filesystems, configures the network, launches getty process, .... Many of these things require changing host-global settings, and if you launch a container with --privileged you're allowing systemd to do that.

I'd give two key recommendations on this command:

Don't run systemd in Docker. If you really need a multi-process init system, supervisord is popular, but prefer single-process containers. If you know you need some init(8) (process ID 1 has some responsibilities) then tini is another popular option.

Don't directly run bare Linux distribution images. Whatever software you're trying to run, it's almost assuredly not in an alpine or ubuntu image. Build a custom image that has the software you need and run that; you should set up its CMD correctly so that you can docker run the image without any manual setup.

Also remember that the ability to run any Docker command at all implies unrestricted root-level access over the host. You're seeing some of that here where a --privileged container is taking over the host's console; it's also very very easy to read and edit files like the host's /etc/shadow and /etc/sudoers. There's nothing technically wrong with the kind of script you're showing, but you need to be extremely careful with standard security concerns.

Upvotes: 2

Related Questions