Run a container

What you will be able to do

• Run a container from Alpine with a command you choose
• Use -it for an interactive shell and --rm to clean up
• Explain why a container exits when its main process exits

Why this matters for DE and AI

docker run is “start this image with this command.” A Spark submit, a dbt run, a one-shot extract — same shape. If you only ever click Start in a GUI, you cannot tell a job that finished from a job that never started.

Concepts

Shape of the command:

docker run [flags] IMAGE [command] [args...]

Examples you will type today:

docker run --rm alpine:3.20 uname -a
docker run --rm -it alpine:3.20 sh

• IMAGE — alpine:3.20 means repository alpine, tag 3.20. First use downloads it.
• command — replaces the image’s default. Alpine’s default is sh; uname -a is more useful for a one-liner.
• --rm — remove the container when it exits. Good for experiments.
• -i — keep stdin open.
• -t — allocate a terminal. Together -it is how you get a prompt inside.

Why it stops

A container lives as long as its main process. uname -a prints and exits — container exits. sleep 300 stays until you stop it or 300 seconds pass. Postgres stays because its server process stays.

That is why a job image with command: python extract.py “dies” when the script ends. That can be success.

--name

Without a name, Docker assigns a random one (funny_einstein). For anything you will logs or stop, pass --name dcubes-…. Names must be unique among existing containers.

Practice on your machine

cd ~/dcubes/docker-lab

Run a one-shot command on Alpine. The first pull is a few megabytes.

docker run --rm alpine:3.20 uname -a

What you should see: a Linux kernel line. You are looking at the container’s uname, not your Mac’s Darwin line. On WSL/Linux it still prints the host kernel (containers share it) but the userland is Alpine.

Print the OS release inside the image:

docker run --rm alpine:3.20 cat /etc/os-release

You should see Alpine Linux.

Now take an interactive shell. -it matters; without it sh looks “stuck” with no prompt.

docker run --rm -it alpine:3.20 sh

Your prompt changes (often / #). You are not in ~/dcubes/docker-lab on the host. This is a tiny Linux filesystem.

Inside the container, run:

pwd
ls /
echo hello from alpine
exit

What you should see: / as the working directory, folders like bin etc tmp, then your host prompt again after exit.

If you get stuck inside, type exit or press Ctrl + D.

Common mistakes

• Forgetting -it. sh with no TTY prints nothing useful. Add -it or pass a non-interactive command (uname -a).
• Typing docker run alpine forever. Without a tag you get latest, which moves. We pin 3.20 in this module.
• Thinking the container has your files. It does not, until you mount them (lesson 8). ls ~/dcubes inside Alpine will fail.

Next

Container lifecycle — names, ps, logs, stop, and rm.