How to enter in a Docker container already running with a new TTY
I have a container that is running the Apache service in the foreground. I would like to be able to access the container from another shell in order to "poke around" inside it and examine the files. At the moment, if I attach to the container, I am left looking at the Apache daemon and cannot run any commands.
Is it possible to attach another tty to a running container? Possibly, I can take advantage of the fact that Docker is actually just wrapping around LXC containers? I have tried sudo lxc-console -n [container-id] -t [1-4] but it appears that only one tty is made available and that is the one running the apache daemon. Perhaps there is a way to enable multiple lxc consoles during the build?
I would rather not configure and build the container with an openssh service if possible.
With docker 1.3, there is a new command docker exec . This allows you to enter a running docker:
docker exec -it [container-id] bash
You should use Jérôme Petazzoni's tool called 'nsenter' to enter a container without using SSH. See: https://github.com/jpetazzo/nsenter
Install with simply running: docker run -v /usr/local/bin:/target jpetazzo/nsenter
Then use the command docker-enter <container-id> to enter the container.
Update
As of docker 0.9, for the steps below to now work, one now has to update the /etc/default/docker file with the '-e lxc' to the docker daemon startup option before restarting the daemon (I did this by rebooting the host).
This is all because...
...it [docker 0.9] contains a new "engine driver" abstraction to make possible the use of other API than LXC to start containers. It also provide a new engine driver based on a new API library (libcontainer) which is able to handle Control Groups without using LXC tools. The main issue is that if you are relying on lxc-attach to perform actions on your container, like starting a shell inside the container, which is insanely useful for developpment environment...
source
Please note that this will prevent the new host only networking optional feature of docker 0.11 from "working" and you will only see the loopback interface. bug report
It turns out that the solution to a different question was also the solution to this one:
...you can use docker ps -notrunc to get the full lxc container ID and then use lxc-attach -n <container_id> run bash in that container as root.
Update: You will soon need to use ps --no-trunc instead of ps -notrunc which is being deprecated.
Find the full container ID
Enter the lxc attach command.
Top shows my apache process running that docker started.