Super short Docker reference

In this age of instant internet wisdom, you can find a guide for just about anything. Consider this your ultra-condensed Docker cheat sheet — the most useful commands, tips, and gotchas that I’ve collected while wrangling containers. Think of it as the espresso shot before the full Docker latte.

Installation

Ubuntu users: Docker is part of the latest Ubuntu versions
MacOs users: you can use the precompiled package directly from the Docker webpage.

Documentation

For more details, the official source is always your friend:

Docker reference manual

Configuration

At its core, a Docker container needs just two files to define its behavior:

docker-compose.yml — orchestrates services, networks, and volumes.
Dockerfile — describes how to build the container environment.

Useful tips

Quick commands and tricks for keeping your Docker life sane.

Useful commands

List all volumes:
docker volume ls

Pro tip: Volumes are where your data lives. Keep an eye on them.

How to change the default data directory

By default, Docker stores containers, images, and volumes in /var/lib/docker. If your root filesystem is limited, this may fill up fast. Here’s how to move it to a new location (Ubuntu/Debian example):

(Extracted from How to Change Docker’s Default Data Directory)

Stop Docker:

sudo systemctl stop docker.service
sudo systemctl stop docker.socket

Create a new location and move the data:

sudo mkdir /data/docker
sudo mv /var/lib/docker /data/docker

Update Docker configuration

Edit the daemon config:
sudo vi /etc/docker/daemon.json
Add the following:
{
    "data-root": "/data/docker"
}

Restart Docker:

sudo systemctl start docker.socket
sudo systemctl start docker.service

Verify that Docker is running:

sudo systemctl status docker

should output something like:

● docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled; preset: enabled)
Active: active (running) since Sat 2025-10-18 11:05:22 EEST; 3h 24min ago
Invocation: f2052aa83cfe491ebed5264d230aa966
TriggeredBy: ● docker.socket
Docs: https://docs.docker.com
Main PID: 2353686 (dockerd)
Tasks: 16
Memory: 37.9M (peak: 41M)
CPU: 38.638s
CGroup: /system.slice/docker.service
     └─2353686 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

Oct 18 14:24:50 deer dockerd[2353686]: time="2025-10-18T14:24:50.662993087+03:00" level=info msg="No non-localhost DNS nameservers >
Oct 18 14:24:50 deer dockerd[2353686]: time="2025-10-18T14:24:50.740593836+03:00" level=info msg="ignoring event" container=dae50ac>

Check that Docker is using the new directory:

$ sudo docker info | grep Root
Docker Root Dir: /data/docker

Cleaning up space

Docker loves to hoard. Let’s declutter.

(Extracted from How to clear Docker cache and free up space on your system)

Check disk usage:
```
docker system df
```

Remove stopped containers:

docker container prune      # Removes all stopped containers

Remove all containers:

docker stop $(docker ps -q) # Stop all containers
docker container prune      # Remove stopped containers

Remove images:

docker image prune -f       # Remove unused images
docker image prune -a -f    # Remove all images

Remove volumes:

docker volume prune -f      # Remove unused volumes
docker volume rm -a         # Remove all volumes

Remove build cache:

docker builder prune        # Old style
docker buildx prune         # New style

Remove everything (use with caution!):
```
docker system prune -f
```

Tip

Think of this like tidying your desk: removing containers and images you no longer need keeps Docker nimble, and saves your storage from quietly mutating into a monster.