Docker Cheatsheet

Installation & Setup

Linux Installation

Install Docker on Ubuntu/Debian systems.

# Update package manager
sudo apt update
# Install prerequisites
sudo apt install apt-transport-https ca-certificates curl
software-properties-common
# Add Docker's official GPG key
curl -fsSL https://download.docker.com/linux/ubuntu/gpg
| sudo apt-key add -
# Add Docker repository
sudo add-apt-repository "deb [arch=amd64]
https://download.docker.com/linux/ubuntu bionic stable"
# Install Docker
sudo apt update && sudo apt install docker-ce
# Start Docker service
sudo systemctl start docker
sudo systemctl enable docker

Windows & macOS

Install Docker Desktop for GUI-based management.

# Windows: Download Docker Desktop from docker.com
# macOS: Use Homebrew or download from docker.com
brew install --cask docker
# Or download directly from:
# https://www.docker.com/products/docker-desktop

Post-Installation Setup

Configure Docker for non-root usage and verify installation.

# Add user to docker group (Linux)
sudo usermod -aG docker $USER
# Log out and back in for group changes
# Verify Docker installation
docker --version
docker run hello-world

Docker Compose Installation

Install Docker Compose for multi-container applications.

# Linux: Install via curl
sudo curl -L
"https://github.com/docker/compose/releases/download
/v2.24.0/docker-compose-$(uname -s)-$(uname -m)" -o
/usr/local/bin/docker-compose
sudo chmod +x /usr/local/bin/docker-compose
# Verify installation
docker-compose --version
# Note: Docker Desktop includes Compose

Basic Docker Commands

System Information: docker version / docker system info

Check Docker installation and environment details.

# Display Docker version information
docker version
# Show system-wide Docker
information
docker system info
# Display help for Docker commands
docker help
docker <command> --help

Running Containers: docker run

Create and start a container from an image.

# Run a container interactively
docker run -it ubuntu:latest bash
# Run container in background
(detached)
docker run -d --name my-container
nginx
# Run with port mapping
docker run -p 8080:80 nginx
# Run with auto-removal after exit
docker run --rm hello-world

List Containers: docker ps

View running and stopped containers.

# List running containers
docker ps
# List all containers (including
stopped)
docker ps -a
# List container IDs only
docker ps -q
# Show latest created container
docker ps -l

Container Management

Container Lifecycle: start / stop / restart

Control container execution state.

# Stop a running container
docker stop container_name
# Start a stopped container
docker start container_name
# Restart a container
docker restart container_name
# Pause/unpause container processes
docker pause container_name
docker unpause container_name

Execute Commands: docker exec

Run commands inside running containers.

# Execute interactive bash shell
docker exec -it container_name bash
# Execute a single command
docker exec container_name ls -la
# Execute as different user
docker exec -u root container_name whoami
# Execute in specific directory
docker exec -w /app container_name pwd

Container Removal: docker rm

Remove containers from the system.

# Remove a stopped container
docker rm container_name
# Force remove a running container
docker rm -f container_name
# Remove multiple containers
docker rm container1 container2
# Remove all stopped containers
docker container prune

Container Logs: docker logs

View container output and debug issues.

# View container logs
docker logs container_name
# Follow logs in real-time
docker logs -f container_name
# Show only recent logs
docker logs --tail 50 container_name
# Show logs with timestamps
docker logs -t container_name

Image Management

Building Images: docker build

Create Docker images from Dockerfiles.

# Build image from current directory
docker build .
# Build and tag an image
docker build -t myapp:latest .
# Build with build arguments
docker build --build-arg VERSION=1.0 -t myapp .
# Build without using cache
docker build --no-cache -t myapp .

Image Inspection: docker images / docker inspect

List and examine Docker images.

# List all local images
docker images
# List images with specific filters
docker images nginx
# Show image details
docker inspect image_name
# View image build history
docker history image_name

Registry Operations: docker pull / docker push

Download and upload images to registries.

# Pull image from Docker Hub
docker pull nginx:latest
# Pull specific version
docker pull ubuntu:20.04
# Push image to registry
docker push myusername/myapp:latest
# Tag image before pushing
docker tag myapp:latest myusername/myapp:v1.0

Image Cleanup: docker rmi / docker image prune

Remove unused images to free disk space.

# Remove a specific image
docker rmi image_name
# Remove unused images
docker image prune
# Remove all unused images (not just dangling)
docker image prune -a
# Force remove image
docker rmi -f image_name

Dockerfile Basics

Essential Instructions

Core Dockerfile commands for building images.

# Base image
FROM ubuntu:20.04
# Set maintainer information
LABEL maintainer="user@example.com"
# Install packages
RUN apt-get update && apt-get install -y \
    python3 \
    python3-pip \
    && rm -rf /var/lib/apt/lists/*
# Copy files from host to container
COPY app.py /app/
# Set working directory
WORKDIR /app
# Expose port
EXPOSE 8000

Runtime Configuration

Configure how the container runs.

# Set environment variables
ENV PYTHON_ENV=production
ENV PORT=8000
# Create user for security
RUN useradd -m appuser
USER appuser
# Define startup command
CMD ["python3", "app.py"]
# Or use ENTRYPOINT for fixed commands
ENTRYPOINT ["python3"]
CMD ["app.py"]
# Set health check
HEALTHCHECK --interval=30s --timeout=3s \
  CMD curl -f http://localhost:8000/ || exit 1

Docker Compose

Basic Compose Commands: docker-compose up / docker-compose down

Start and stop multi-container applications.

# Start services in foreground
docker-compose up
# Start services in background
docker-compose up -d
# Build and start services
docker-compose up --build
# Stop and remove services
docker-compose down
# Stop and remove with volumes
docker-compose down -v

Service Management

Control individual services within Compose applications.

# List running services
docker-compose ps
# View service logs
docker-compose logs service_name
# Follow logs for all services
docker-compose logs -f
# Restart a specific service
docker-compose restart service_name

Sample docker-compose.yml

Example multi-service application configuration.

version: '3.8'
services:
  web:
    build: .
    ports:
      - "8000:8000"
    environment:
      -
DATABASE_URL=postgresql://user:pass@db:5432/myapp
    depends_on:
      - db
    volumes:
      - .:/app

  db:
    image: postgres:13
    environment:
      POSTGRES_DB: myapp
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
    volumes:
      - db_data:/var/lib/postgresql/data
volumes:
  db_data:

Networking & Volumes

Container Networking

Connect containers and expose services.

# List networks
docker network ls
# Create a custom network
docker network create mynetwork
# Run container on specific network
docker run --network mynetwork nginx
# Connect running container to network
docker network connect mynetwork container_name
# Inspect network details
docker network inspect mynetwork

Port Mapping

Expose container ports to the host system.

# Map single port
docker run -p 8080:80 nginx

# Map multiple ports
docker run -p 8080:80 -p 8443:443 nginx
# Map to specific host interface
docker run -p 127.0.0.1:8080:80 nginx
# Expose all ports defined in image
docker run -P nginx

Data Volumes: docker volume

Persist and share data between containers.

# Create a named volume
docker volume create myvolume
# List all volumes
docker volume ls
# Inspect volume details
docker volume inspect myvolume
# Remove volume
docker volume rm myvolume
# Remove unused volumes
docker volume prune

Volume Mounting

Mount volumes and host directories in containers.

# Mount named volume
docker run -v myvolume:/data nginx
# Mount host directory (bind mount)
docker run -v /host/path:/container/path nginx
# Mount current directory
docker run -v $(pwd):/app nginx
# Read-only mount
docker run -v /host/path:/container/path:ro nginx

Container Inspection & Debugging

Container Details: docker inspect

Get detailed information about containers and images.

# Inspect container configuration
docker inspect container_name
# Get specific information using format
docker inspect --format='{{.State.Status}}'
container_name
# Get IP address
docker inspect --format='{{.NetworkSettings.IPAddress}}'
container_name
# Get mounted volumes
docker inspect --format='{{.Mounts}}' container_name

Resource Monitoring

Monitor container resource usage and performance.

# Show running processes in container
docker top container_name
# Display live resource usage statistics
docker stats
# Show stats for specific container
docker stats container_name
# Monitor events in real-time
docker events

File Operations: docker cp

Copy files between containers and host system.

# Copy file from container to host
docker cp container_name:/path/to/file ./
# Copy file from host to container
docker cp ./file container_name:/path/to/destination
# Copy directory
docker cp ./directory
container_name:/path/to/destination/
# Copy with archive mode to preserve permissions
docker cp -a ./directory container_name:/path/

Troubleshooting

Debug container issues and connectivity problems.

# Check container exit code
docker inspect --format='{{.State.ExitCode}}'
container_name
# View container processes
docker exec container_name ps aux
# Test network connectivity
docker exec container_name ping google.com
# Check disk usage
docker exec container_name df -h

Registry & Authentication

Docker Hub Operations: docker login / docker search

Authenticate and interact with Docker Hub.

# Login to Docker Hub
docker login
# Login to specific registry
docker login registry.example.com
# Search for images on Docker Hub
docker search nginx
# Search with filter
docker search --filter stars=100 nginx

Image Tagging & Publishing

Prepare and publish images to registries.

# Tag image for registry
docker tag myapp:latest username/myapp:v1.0
docker tag myapp:latest
registry.example.com/myapp:latest
# Push to Docker Hub
docker push username/myapp:v1.0
# Push to private registry
docker push registry.example.com/myapp:latest

Private Registry

Work with private Docker registries.

# Pull from private registry
docker pull registry.company.com/myapp:latest
# Run private registry locally
docker run -d -p 5000:5000 --name registry registry:2
# Push to local registry
docker tag myapp localhost:5000/myapp
docker push localhost:5000/myapp

Image Security

Verify image integrity and security.

# Enable Docker Content Trust
export DOCKER_CONTENT_TRUST=1
# Sign and push image
docker push username/myapp:signed
# Verify image signatures
docker trust inspect username/myapp:signed
# Scan images for vulnerabilities
docker scan myapp:latest

System Cleanup & Maintenance

System Cleanup: docker system prune

Remove unused Docker resources to free disk space.

# Remove unused containers, networks, images
docker system prune
# Include unused volumes in cleanup
docker system prune -a --volumes
# Remove everything (use with caution)
docker system prune -a -f
# Show space usage
docker system df

Targeted Cleanup

Remove specific types of unused resources.

# Remove stopped containers
docker container prune
# Remove unused images
docker image prune -a
# Remove unused volumes
docker volume prune
# Remove unused networks
docker network prune

Bulk Operations

Perform operations on multiple containers/images.

# Stop all running containers
docker stop $(docker ps -q)
# Remove all containers
docker rm $(docker ps -aq)
# Remove all images
docker rmi $(docker images -q)
# Remove dangling images only
docker rmi $(docker images -f "dangling=true" -q)

Resource Limits

Control container resource consumption.

# Limit memory usage
docker run --memory=512m nginx
# Limit CPU usage
docker run --cpus="1.5" nginx
# Limit both CPU and memory
docker run --memory=1g --cpus="2.0" nginx
# Set restart policy
docker run --restart=always nginx

Docker Configuration & Settings

Daemon Configuration

Configure the Docker daemon for production use.

# Edit daemon configuration
sudo nano
/etc/docker/daemon.json
# Example configuration:
{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  },
  "storage-driver": "overlay2"
}
# Restart Docker service
sudo systemctl restart docker

Environment Variables

Configure Docker client behavior with environment variables.

# Set Docker host
export
DOCKER_HOST=tcp://remote-
docker:2376
# Enable TLS verification
export DOCKER_TLS_VERIFY=1
export
DOCKER_CERT_PATH=/path/to/c
erts
# Set default registry
export
DOCKER_REGISTRY=registry.co
mpany.com
# Debug output
export DOCKER_BUILDKIT=1

Performance Tuning

Optimize Docker for better performance.

# Enable experimental features
echo '{"experimental": true}' |
sudo tee
/etc/docker/daemon.json
# Set storage driver options
{
  "storage-driver": "overlay2",
  "storage-opts": [

"overlay2.override_kernel_check
=true"
  ]
}
# Configure logging
{
  "log-driver": "syslog",
  "log-opts": {"syslog-address":
"udp://logs.company.com:514"}
}

Best Practices

Security Best Practices

Keep your containers secure and production-ready.

# Run as non-root user in Dockerfile
RUN groupadd -r appuser && useradd -r -g appuser
appuser
USER appuser
# Use specific image tags, not 'latest'
FROM node:16.20.0-alpine
# Use read-only filesystems when possible
docker run --read-only nginx

Performance Optimization

Optimize containers for speed and resource efficiency.

# Use multi-stage builds to reduce image size
FROM node:16 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
FROM node:16-alpine
WORKDIR /app
COPY --from=builder /app/node_modules
./node_modules
COPY . .
CMD ["node", "server.js"]

Relevant Links

• Kubernetes Cheatsheet
• Linux Cheatsheet
• Shell Cheatsheet
• DevOps Cheatsheet
• Ansible Cheatsheet
• Git Cheatsheet
• Red Hat Enterprise Linux Cheatsheet
• Python Cheatsheet