Start a screen session inside LXD-managed container

Question

I'd like to start a screen session inside an LXD-managed container so that I could detach running processes and maybe re-attach in the future when I want to check on their status.

I tried to attach to the container running

$ lxc exec my-ubuntu -- /bin/bash

and then start a session with screen -x, but I get the following error:

Must be connected to a terminal.

I can see that many people have had a similar problem when trying to initiate screen from ssh, but I couldn't apply the suggested solution to my case.

Solution

For LXD using

lxc exec my-ubuntu -- sh -c "exec >/dev/tty 2>/dev/tty </dev/tty && /usr/bin/screen -s /bin/bash"

or

lxc exec my-ubuntu -- sh -c "exec >/dev/tty 2>/dev/tty </dev/tty && /usr/bin/screen -x"

or with any other screen switch.

---

The same for Docker ;)

docker run -it my-ubuntu sh -c "exec >/dev/tty 2>/dev/tty </dev/tty && /usr/bin/screen -s /bin/bash"

Comments

[Leon Straathof]

Terrific. But how can I then work with screen the way I normally do, monitor which sessions are running and re-attach to a specific one?

[A.B.]

I don't understand. In the same way as before. E.g. using -R.

[A.B.]

Answer updated.

[Leon Straathof]

Well, I would normally do screen -x, but trying lxc exec my-ubuntu -- sh -c "exec >/dev/tty 2>/dev/tty </dev/tty && /usr/bin/screen -x doesn't work, and neither does lxc exec my-ubuntu -- sh -c "exec >/dev/tty 2>/dev/tty </dev/tty && /usr/bin/screen -r <pid>.tty.my-ubuntu". Nor can I do screen -x from within bash in the container.

[A.B.]

What's about -R

[Leon Straathof]

I should specify: the reason ... screen -x fails is because I get There are several suitable screens on: followed by a list of sessions. Same with screen -R.

[A.B.]

Perhaps you should ask a new question for this problem. :) seems to be a little bit complicated.

[Leon Straathof]

There aren't any answers there, but I'd like to mention that I did open a new question regarding this issue here. I also suggested a walk-around on that question.

[LUser]

@JonathanY. just run script /dev/null and then run screen.