Docker – Containers & Shells

Docker containers provide isolated environments for applications, but sometimes you need to interact with the container directly. Using shells, you can access a running container, execute commands, debug issues, and manage its environment effectively.

Accessing a Docker Container

To interact with a container, you can attach a shell session using docker exec or docker attach. This allows you to run commands inside the container as if you were logged into a standalone system.

Using docker exec

# Access container shell interactively
docker exec -it  /bin/bash

# Run a command directly inside the container
docker exec  ls /app

Using docker attach

# Attach to a running container's terminal
docker attach 

# Detach without stopping the container (Press Ctrl + P, Ctrl + Q)

Checking Running Processes

You can list all processes running inside a container using ps or Docker-specific commands:

# List processes inside container
docker exec -it  ps aux

# View container stats and resource usage
docker stats 

Copying Files In and Out of Containers

Docker provides commands to copy files between host and container environments:

# Copy file from host to container
docker cp ./localfile.txt :/app/localfile.txt

# Copy file from container to host
docker cp :/app/file.txt ./file.txt

Inspecting Container Environment

You can inspect the container’s configuration, environment variables, and network settings using:

# View environment variables
docker exec -it  printenv

# Inspect container details
docker inspect 

Best Practices When Using Shells

• Use docker exec instead of docker attach for safer interactive sessions.
• Do not make persistent changes inside containers; rebuild images for long-term changes.
• Use docker logs to check application output instead of constantly accessing shells.
• Keep containers minimal and secure; avoid installing unnecessary packages just for debugging.
• Detach safely from a container to avoid stopping it unintentionally.

Conclusion

Mastering Docker shells allows you to troubleshoot, debug, and manage running containers efficiently. This hands-on access is essential for developers and DevOps engineers to maintain containerized applications in production and development environments.