Docker Troubleshooting

A troubleshooting guide for common Docker problems.

Container Won't Start

# Check the logs
docker logs container_name

# Check the status
docker inspect container_name

# Run for debugging
docker run -it image_name sh

Build Fails

# Build with verbose output
docker build -t myapp . 2>&1 | tee build.log

# Build without cache
docker build --no-cache -t myapp .

# Check the Dockerfile
cat Dockerfile

Network Issues

# Check the network
docker network inspect bridge

# Check port mapping
docker port container_name

# Test the connection
docker exec container_name ping google.com

Volume Issues

# Check the volume
docker volume inspect volume_name

# Check the mount point
docker inspect container_name | grep Mounts

# Check permissions
docker exec container_name ls -la /path

Use Case: Troubleshooting

# Problem: Container crashes
docker logs api
# Error: EACCES: permission denied

# Solution: Fix the permissions
docker run --rm -v $(pwd):/app -w /app node:18 chown -R node:node /app

# Problem: Port conflict
docker run -d -p 80:80 nginx
# Error: Bind for 0.0.0.0:80 failed: port is already allocated

# Solution: Check which port is in use
lsof -i :80
# or use a different port
docker run -d -p 8080:80 nginx

Common Errors

"No space left on device"

# Cleanup
docker system prune -a --volumes

# Check disk usage
docker system df

"Cannot connect to Docker daemon"

# Start Docker
sudo systemctl start docker

# Check the status
sudo systemctl status docker

"Image not found"

# Check the image
docker images | grep myapp

# Rebuild
docker build -t myapp .

Everyday Use Case

Case: A developer runs into an error when running a container.

# Debug the container
docker run -it --rm myapp sh

# Check the environment
docker exec api env

# Check the network
docker network inspect bridge

Log Analysis

# Search for errors
docker logs api 2>&1 | grep -i error

# Export the logs
docker logs api > api.log 2>&1

# View the latest logs
docker logs --tail 100 api

Best Practices

Check the logs first: docker logs container_name
Use --rm: For debugging containers
Check resources: docker stats
Read the documentation: Docker docs for specific errors
Community: Stack Overflow, Docker forums

Conclusion

Troubleshooting Docker requires a systematic approach. Check the logs, inspect the container, and use debugging tools to resolve the problem.