Interactive mode

Learn the interactive terminal with -it flags.

Interactive mode

To work with a shell inside a container, two flags are used together: -i (interactive) keeps standard input open, -t (tty) allocates a terminal. They are usually written as -it:

$ docker run -it ubuntu:24.04 bash
root@3a4b5c6d7e8f:/# ls
bin  boot  dev  etc  home  ...
root@3a4b5c6d7e8f:/# exit

Here the main process is bash; typing exit closes the shell and the container stops.

Detaching and reattaching

To leave an interactive container's terminal without stopping it, press Ctrl+P, Ctrl+Q. Later, docker attach reconnects to the main process. For debugging, docker exec -it, which opens a new shell, is usually safer:

docker run -dit --name kutu alpine sh   # in the background with -d, but with a TTY
docker attach kutu                      # attach to the main process
docker exec -it kutu sh                 # open a separate shell

Exercise A temporary shell

Write the command that opens an interactive sh shell in the alpine:3.20 image and deletes the container on exit.

Test yourself

What happens when you type exit in a bash shell opened with docker run?
- A new shell opens
- The container stops because the main process ended
- The container keeps running in the background
- The container is removed
Show answer

The container stops because the main process ended — Unlike a shell opened with exec, here bash is the main process.

Open an interactive shell.

docker run ____ ubuntu:24.04 bash

Show answer

docker run -it ubuntu:24.04 bash

Match.

-i

Keeps input open
-t

Allocates a terminal
Ctrl+P, Ctrl+Q

Detach without stopping
docker attach

Attach to the main process

Next lesson: Naming containers

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