DEV Community

Alex Spinov
Alex Spinov

Posted on

9 Docker Commands That Save Hours (But Nobody Teaches You)

#beginners #docker #devops #tutorial

Most developers know docker run and docker-compose up. Here are 9 Docker commands that save hours but nobody teaches you.

1. docker system df — See What's Eating Your Disk 

docker system df
Enter fullscreen mode Exit fullscreen mode 
TYPE            TOTAL   ACTIVE  SIZE    RECLAIMABLE
Images          47      3       12.4GB  11.2GB (90%)
Containers      12      1       2.3GB   2.1GB (91%)
Local Volumes   8       2       4.1GB   3.8GB (92%)
Build Cache     0       0       0B      0B
Enter fullscreen mode Exit fullscreen mode

90% of your Docker disk usage is reclaimable. You're wasting gigabytes.

2. docker system prune -a — Reclaim Everything 

docker system prune -a --volumes
Enter fullscreen mode Exit fullscreen mode

This removes:

  • All stopped containers
  • All unused networks
  • All unused images (not just dangling)
  • All unused volumes

I freed 38GB on my dev machine. Check yours.

3. docker stats — Real-Time Resource Monitor 

docker stats --format "table {{.Name}}  {{.CPUPerc}}    {{.MemUsage}}"
Enter fullscreen mode Exit fullscreen mode 
NAME          CPU %    MEM USAGE / LIMIT
postgres      0.15%    125MiB / 8GiB
redis         0.08%    12MiB / 8GiB
web-app       2.34%    456MiB / 8GiB
Enter fullscreen mode Exit fullscreen mode

Better than htop for finding container memory leaks.

4. docker exec with Environment Variables 

docker exec -e DEBUG=true -e LOG_LEVEL=verbose my-container python3 debug.py
Enter fullscreen mode Exit fullscreen mode

Inject env vars into a running container without restarting. Perfect for debugging production issues.

5. docker cp — Copy Files In/Out of Containers 

# Copy logs out of a container
docker cp my-container:/var/log/app.log ./app.log

# Copy config into a container
docker cp ./config.yml my-container:/etc/app/config.yml
Enter fullscreen mode Exit fullscreen mode

No volume mount needed. Works on running or stopped containers.

6. docker diff — See What Changed Inside a Container 

docker diff my-container
Enter fullscreen mode Exit fullscreen mode 
C /var/log
A /var/log/app.log
C /tmp
A /tmp/cache.db
D /etc/old-config.yml
Enter fullscreen mode Exit fullscreen mode

A = added, C = changed, D = deleted. Instant forensics.

7. docker history — Understand Image Layers 

docker history --no-trunc --format "{{.Size}}   {{.CreatedBy}}" my-image | head -10
Enter fullscreen mode Exit fullscreen mode

Find which Dockerfile instruction made your image 2GB. Usually it's COPY . . including node_modules.

8. docker compose up --build --force-recreate 

docker compose up --build --force-recreate --remove-orphans -d
Enter fullscreen mode Exit fullscreen mode

The nuclear option: rebuilds images, recreates containers, removes orphans. Use when "works on my machine" meets "doesn't work in Docker."

9. docker logs with Timestamps and Follow 

docker logs --since 5m --follow --timestamps my-container 2>&1 | grep ERROR
Enter fullscreen mode Exit fullscreen mode

Tail logs from the last 5 minutes, with timestamps, filtered to errors. Better than scrolling through 10,000 lines.

Bonus: One-Liner Health Check 

docker ps --format '{{.Names}}: {{.Status}}' | grep -v "healthy"
Enter fullscreen mode Exit fullscreen mode

Instantly find unhealthy containers.

I share practical developer tools and CLI tricks weekly. Follow for more time-saving commands.

Need automated infrastructure monitoring or web scraping? Email me at spinov001@gmail.com

Top comments (0)