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Docker Commands

Docker is a containerization system that packages and runs applications with their dependencies inside containers. There are several Docker commands you must know when working with Docker.

Docker Post-Installation Setup

Run Docker as Non-Root User

To create the docker group and add your user:

  1. Create the docker group:

    sudo groupadd docker

  2. Add your user to the docker group:

    sudo usermod -aG docker $USER

  3. Activate the changes to groups:

    newgrp docker

  4. Verify that you can run docker commands without sudo:

    docker images

Essential Docker Commands

1. Docker Version

To find the installed Docker version:

docker --version

Example output:

Docker version 27.3.1, build ce12230

2. Downloading an Image

To work with any Docker image, we need to download it first:

docker pull <IMAGE>

Example of pulling Alpine image:

docker pull alpine:latest

3. List All Docker Images

To list all images available locally on your host machine:

docker images

Example output:

REPOSITORY   TAG      IMAGE ID       CREATED        SIZE
alpine       latest   c059bfaa849c   6 weeks ago    7.39MB
postgres     16       abc123xyz456   2 days ago     229MB

4. Run Docker Image

The docker run command creates a writeable container layer over the specified image and starts it:

docker run [options] <IMAGE>

Common options:

  • -d - Run in detached mode (background)
  • -it - Interactive mode with terminal
  • -p - Publish container port to host
  • -v - Mount volume
  • --name - Assign a name to the container
  • --rm - Automatically remove container when it exits

Explore all options here

Example of running Alpine image with interactive terminal:

docker run -it alpine:latest
# or
docker run -it alpine:latest sh

5. List Running Containers

The docker ps command lists only running containers:

docker ps

Example output:

CONTAINER ID   IMAGE          COMMAND       CREATED        STATUS        PORTS     NAMES
8973c7347905   alpine:latest  "/bin/sh"     2 minutes ago  Up 2 minutes            ecstatic_jang

To list all containers including stopped ones:

docker ps -a

6. Access a Running Container

The docker exec command runs a new command in a running container:

docker exec [options] <CONTAINER_ID> <COMMAND>

Explore options here

Example: Execute into a running Alpine container and create files:

# First, get container ID from docker ps
docker ps

# Then exec into it
docker exec -it 8973c7347905 sh

# Inside container:
/ # mkdir demo
/ # cd demo
/demo # touch helloworld.txt
/demo # ls
helloworld.txt
/demo # exit

Commands used inside container:

  • mkdir - Create directory
  • cd - Change directory
  • touch - Create empty file
  • ls - List files

7. Stop a Container

Stop a running container:

docker stop [OPTIONS] <CONTAINER_ID>

Explore options here

Example:

docker stop 8973c7347905

Once stopped, the container still exists locally but is not running.

8. Start a Stopped Container

Start a stopped container:

docker start [OPTIONS] <CONTAINER_ID>

Explore options here

Example:

# First list all containers to find the stopped one
docker ps -a

# Start it
docker start 8973c7347905

9. Remove a Container

Remove one or more containers:

docker rm [OPTIONS] <CONTAINER_ID>

Explore options here

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

docker rm -f 8973c7347905

10. Remove an Image

Remove local images:

docker rmi [OPTIONS] <IMAGE_ID> or <IMAGE_NAME>

Example:

docker rmi c059bfaa849c
# or by name
docker rmi alpine:latest

To force removal:

docker rmi -f alpine:latest

11. View Container Logs

View logs from a container:

docker logs <CONTAINER_ID>

Follow logs in real-time:

docker logs -f <CONTAINER_ID>

12. Remove All Stopped Containers

Clean up all stopped containers:

docker container prune

13. Remove All Unused Images

Clean up all unused images:

docker image prune -a

Quick Reference Card

Command Description
docker --version Show Docker version
docker pull <img> Download an image
docker images List local images
docker run <img> Run a container
docker ps List running containers
docker ps -a List all containers
docker exec <id> <cmd> Execute command in container
docker stop <id> Stop a container
docker start <id> Start a stopped container
docker rm <id> Remove container
docker rmi <img> Remove image
docker logs <id> Show container logs
docker system prune Remove unused data