Running Your First Docker Container Docker Commands

Learning objective: By the end of this lesson, students will be able to execute key Docker commands to create, monitor, manage, remove containers, and view container logs.

source

Docker Commands

This lesson introduces key Docker commands that help us manage containers and images. By understanding these commands, you’ll be able to create, monitor, and clean up containers in a way that optimizes your system resources.

1. docker run

The docker run command does two things:

• It creates a container from a Docker image.
• It starts the container by executing its default startup command.

docker run <image-name>

Example: Overriding the Default Command

You can also override the default startup command in an image.

docker run <image name> <command-to-override>

For example, to list files in the busybox image:

docker run busybox ls

2. docker ps

The docker ps command lists active containers and their statuses. It’s useful for monitoring what’s running and checking details like container ID, image used, and uptime.

docker ps

If no containers are currently running, the command will return no results. To see this in action, first try running:

docker run busybox ping google.com

In another terminal window, run docker ps to view the running container. You’ll see something like:

CONTAINER ID   IMAGE     COMMAND             CREATED         STATUS         PORTS     NAMES
f7eea52fa97e   busybox   "ping google.com"   7 seconds ago   Up 6 seconds             jovial_nash

To stop this container, press Ctrl+C in the terminal running the ping command.

jovial_nash is just a randomly generated name to identify this container.

Showing All Containers

To list all containers, including those that have stopped, use:

docker ps --all

The output will look something like this:

CONTAINER ID  IMAGE        COMMAND            CREATED         STATUS                   PORTS  NAMES
2ce9bdb14238  hello-world  "/hello"           52 minutes ago  Created                         vibrant_benz
f7eea52fa97e  busybox      "ping google.com"  17 hours ago    Exited (0) 17 hours ago         jovial_nash
570646e6503c  busybox      "ls"               17 hours ago    Exited (0) 17 hours ago         intelligent_lederberg

3. docker start

Use docker start to restart a container that has been created or stopped, allowing you to reuse containers without creating new ones each time.

docker start <container-id>

To attach the container’s output to your terminal (useful for monitoring logs), include the -a flag:

docker start -a <container-id>

4. docker stop and docker kill

These commands stop a running container.

• docker stop sends a SIGTERM signal (short for terminate signal), giving the container a chance to finish any cleanup tasks.
• docker kill sends a SIGKILL signal, immediately stopping the container without cleanup time.

Use docker stop when you want a graceful shutdown and docker kill if the container is unresponsive.

Example

Run a command to keep a container active:

docker run busybox ping google.com

To stop it, find the container ID with docker ps, then run:

docker stop <container-id>

5. docker logs

This command retrieves the log output of a container, whether it’s currently running or has stopped. Use the container ID to view logs.

docker logs <container-id>

This is especially helpful for troubleshooting containers that have exited unexpectedly.

Important Note: You don’t need to type the entire container ID to run a command. As long as the first few characters are unique to that container, Docker can identify it. For example, if your container ID is 3ddc6041a39d, you can simply use docker stop 3dd, and Docker will still recognize the container.

6. docker pull

The docker pull command downloads existing images from a Docker registry (like Docker Hub) to your local machine.

• When to Use:
  • When you need a pre-built image that is publicly available or that you have previously built and pushed to a registry.
  • When you want to update an existing image to the latest version.

Example

docker pull ubuntu:latest

7. docker build

The docker build command creates a new Docker image from a Dockerfile, which contains a set of instructions on how to build that image.

• When to Use:
  • When you have custom application code or configurations that need to be included in a Docker image.
  • When you want to create an image that includes specific dependencies or configurations tailored to your application.

Example

docker build -t my-custom-image:latest .

8. docker exec

The docker exec command lets you run additional commands in a running container, such as launching an interactive shell.

docker exec -it <container-id> /bin/sh

The -it flag makes the terminal interactive, so you can use shell commands like ls and cd to explore the container. Type exit to leave the shell.

9. docker rm

The docker rm command removes stopped containers, freeing up resources.

docker rm <container-id>

Forcing Removal of Running Containers

To remove a running container, use the -f or --force flag:

docker rm -f <container-id>

10. docker image ls

Lists all images in your local Docker cache, which stores downloaded images to speed up future container creation.

docker image ls

11. docker system prune

This command cleans up unused resources, including stopped containers, networks, dangling images, and build cache.

⚠ Important Note: Do not run this command on your VM, as it will delete necessary files for upcoming lessons.

docker system prune  ***DO NOT RUN***

This command will generally produce a prompt like this:

WARNING! This will remove:

- all stopped containers
- all networks not used by at least one container
- all dangling images
- all dangling build cache

Are you sure you want to continue? [y/N]

Always be sure you’re okay with deleting these items before proceeding.