Running Containers

docker run — The One Command That Does It All

docker run is the command you will use the most. It does three things in one go: finds the image, creates a container from it, and starts it.

docker run nginx:1.25

Run that and… nothing visible happens. The terminal just hangs. That is correct — nginx is a web server that keeps running until you stop it. Press Ctrl + C to stop it.

Now let us add flags one at a time to make this actually useful.

-d: Run in the Background

The -d flag stands for detached. It starts the container in the background so your terminal is free to use.

docker run -d nginx:1.25

Docker prints the container ID and gives you your prompt back:

3f4a8b12cd90e1a2...

-p: Open a Port

A container is isolated — you cannot reach it from your browser yet. The -p flag creates a tunnel: your machine port → container port.

docker run -d -p 8080:80 nginx:1.25

Read -p 8080:80 as: “when I visit port 8080 on my machine, forward the traffic to port 80 inside the container.”

Side	Port	Meaning
Left of :	8080	Your machine (host) — you choose this
Right of :	80	Inside the container — nginx listens here

Now open your browser and go to http://localhost:8080. You will see the nginx welcome page.

—name: Give It a Friendly Name

By default Docker gives your container a random name like sleepy_newton. Use --name to give it something meaningful:

docker run -d -p 8080:80 --name my-webserver nginx:1.25

Now you can refer to the container by name in every subsequent command instead of copying a long ID.

See What Is Running

List all running containers:

docker ps

CONTAINER ID   IMAGE        COMMAND   CREATED        STATUS        PORTS                  NAMES
3f4a8b12cd90   nginx:1.25   ...       2 minutes ago  Up 2 minutes  0.0.0.0:8080->80/tcp   my-webserver

To also see containers that have stopped:

docker ps -a

The -a flag means all (running + stopped).

Stop, Start, and Remove

Three simple commands control the lifecycle of a container:

# Stop a running container (graceful shutdown)
docker stop my-webserver

# Start it again
docker start my-webserver

# Remove it completely (must be stopped first)
docker rm my-webserver

If you want to stop and remove in one go, use the -f (force) flag with rm:

docker rm -f my-webserver

-it: Go Inside a Container

Sometimes you want to open a shell inside a running container to look around. The -it flag does that:

docker run -it ubuntu:22.04 bash

This drops you into a bash shell inside an Ubuntu container. You can run commands, look at files, check what is installed — then type exit to leave.

Summary: The Commands You Now Know

Command	What it does
docker run -d -p 8080:80 --name web nginx:1.25	Run nginx in background, expose on port 8080, name it “web”
docker ps	List running containers
docker ps -a	List all containers (running + stopped)
docker stop web	Stop a container
docker start web	Start a stopped container
docker rm web	Delete a container
docker run -it ubuntu bash	Open a shell inside a container

Next up: stop relying on other people’s images and build your own — with a Dockerfile.