Managing Containers

Once you’ve started your first container, you need to know how to interact with it, check its status, and properly shut it down.

Key Docker Commands for Managing Containers

1. `docker ps` (List Running Containers)

This command shows you all the containers that are currently active.

Tip: Use docker ps -a to see all containers, including those that have stopped.

2. `docker stop <container_id>`

Gracefully shuts down a running container. It’s like turning off a computer correctly.

3. `docker start <container_id>`

Restarts a container that was previously stopped. All its settings and files stay the same.

4. `docker rm <container_id>`

Deletes a container permanently. This is useful for cleaning up your system after you’re done with a task.

Note: You must stop a container before you can remove it.

5. `docker logs <container_id>`

Shows everything that has been printed to the console inside the container. This is your most important tool for debugging!

The Lifecycle of a Container

       [ CREATE ] (docker run)
           ↓
       [ RUNNING ] (active instance)
           ↓
       [ STOPPED ] (docker stop)
           ↓
       [ REMOVED ] (docker rm)

Interacting with a Running Container

Sometimes you need to “log in” to a container to see what’s happening inside.

docker exec -it <container_id> sh

This command opens a terminal inside the running container. You can now explore the file system, check environment variables, and run commands.

How Junior Developers Encounter This

“Is the server running?”: (Using docker ps to verify).
“I need to check the error message”: (Using docker logs).
“I want to clean up my machine”: (Using docker rm on old containers).

Common Beginner Mistakes

Leaving Thousands of Stopped Containers: Every time you run docker run, a new container is created. If you don’t use docker rm, your hard drive will fill up!
Not Using Names: Instead of remembering a long ID like afdd53b, you can name your container with --name my-cool-app when you run it.
Stopping Docker Desktop Instead of Containers: While this works, it’s like unplugging the whole server rack instead of just turning off one server.

Next Lesson

Learn how to create your own custom images from scratch:

➡ Dockerfile Basics