Docker has become a cornerstone in the modern software development landscape. It empowers developers to package and run applications in a consistent and portable manner, irrespective of the underlying infrastructure. This guide serves as a gentle introduction to Docker, delving into the essential commands that will kickstart your journey into the world of containers. 1. Verifying Docker Installation:# The first step is to verify that is installed on your system. Run the following command: Docker sudo docker --version This command displays the installed Docker version. 2. Running the “Hello World” Application:# To experience the magic of Docker firsthand, let’s run the “hello-world” application: sudo docker run hello-world This command fetches the “hello-world” image from Docker Hub and executes it, displaying a simple message on your console. 3. Listing Running Containers:# Docker allows you to manage multiple containers simultaneously. To view a list of all running containers, use the following command: sudo docker ps This command displays a table with information about each running container, including its ID, image name, status, and ports. 4. Launching an Interactive Container:# One of Docker’s key features is the ability to run applications in an isolated environment. To experience this, let’s launch an interactive container based on the Ubuntu image: sudo docker run -it ubuntu bash This command not only starts the container but also provides you with a terminal inside the container, allowing you to execute commands and interact with the system as if it were a regular machine. 5. Searching for Images:# Docker Hub, a public registry, hosts a vast collection of images. You can search for images by name, description, or other criteria using the following command: sudo docker search ubuntu This command searches for images containing the keyword “ubuntu” and displays a list of relevant results. 6. Running a Command Inside a Container:# Often, you may want to run specific commands within a container. To achieve this, you can combine the run command with the -it flag and specify the desired command: sudo docker run -it ubuntu bash
sudo apt-get update This example updates the package list inside the Ubuntu container. 7. Diving Deeper with docker info:# For a comprehensive overview of your Docker environment, use the info command: sudo docker info This command provides detailed information about the Docker daemon, including its configuration, network settings, and storage options. 8. Exploring All Containers:# By default, docker ps only lists running containers. To view all containers, including those that have stopped, use the -a flag: sudo docker ps
sudo docker ps -a The first command displays only running containers, while the second command shows both running and stopped containers. 9. Alternative Listing Formats:# Docker provides various options for customizing the output of the docker ps command. The -l flag allows you to specify the desired format, such as JSON or table: sudo docker container ls
sudo docker container ls -a The container ls command is an alias for docker ps. The first command lists all running containers in a table format, while the second command, with the -a flag, lists all containers (running and stopped) in a table format. 10. Mastering Container Management:# Now that you’ve gained familiarity with basic commands let’s delve into container management, covering operations such as starting, stopping, removing, and restarting containers. 11. Initiating a Container:# To start a container, use the run command with the -it flag for an interactive session: sudo docker run -it centos bash This command starts a container based on the CentOS image and provides you with a terminal inside the container. 12. Halting a Container:# To stop a running container, use the stop command: sudo docker stop <container_id> Replace <container_id> with the ID of the container you want to stop. 13. Removing a Container:# Once you’re done with a container, you can remove it using the rm command: sudo docker rm <container_id> This command removes the specified container from your system. 14. Restarting a Container:# To restart a stopped container, use the restart command: sudo docker restart <container_id> This command restarts. 15. Running a CentOS Container:# sudo docker container run -it centos:7 bash sudo: Grants root privileges for container operations. Docker container run: Creates a new Docker container. -it: Allocates a pseudo-terminal (interactive shell) for interacting with the container. centos:7: Specifies the Docker image to use (CentOS version 7). bash: Launches a Bash shell within the container. 16. System Update:# sudo yum -y update sudo: Again, for root privileges (package management often requires them). Yum: I am the package manager for RPM-based systems like CentOS. -y: Automatically confirms any prompts during the update process (use with caution in production environments). Update: Updates system packages to their latest versions. 17. Listing Directory Contents:# ls -l ls: Lists files and directories. -l: Provides detailed information in a long format (including permissions, owner, group, size, and timestamps). 18. Creating a File:# echo "we are here" > example.org echo: Prints text to the terminal or a file. “we are here”: The text to be written. : Redirects the output to a file (creates example.org in this case) 19. Verifying File Creation:# ls -l Lists the directory contents again, showing the newly created example.org. 20. Viewing File Contents:# cat example.org cat: Displays the contents of a file. example.org: The file to display. 21. Exiting the Container:# exit Terminates the interactive shell session within the container. 22. Listing Running Containers:# sudo docker ps sudo: For root privileges. docker ps: Lists currently running Docker containers. 23. Listing All Containers (Including Stopped Ones):# sudo docker ps -a -a: Shows all containers, regardless of their running state. 24. Running Another Container:# sudo docker container run -it centos:7 bash Re-runs the container creation command from step 1. 25. Exiting the Second Container:# exit Terminates the shell session within the second container 26. Listing All Containers Again:# sudo docker ps -a Verifies both containers are listed. 27. Starting a Stopped Container:# sudo docker container start [containerid] start: Attempts to start a stopped container. [containerid]: Replace this with the actual ID of the container you want to start (obtainable from docker ps -a). 28. Verifying the Started Container:# sudo docker ps Checks if the previously stopped container is now listed as running. 29. Inspecting Processes Within a Container:# sudo docker container exec [containerid] ps -ef exec: Executes a command within a running container. [containerid]: The ID of the container to access. ps -ef: Lists all processes running inside the container (similar to ps -aux on Linux). 30. Interactive Access to the Container:# sudo docker container exec -it [containerid] bash -it: Allocates a pseudo-terminal for interactive interaction. Provides access to the Bash shell within the specified container, allowing you to execute further commands. 31. Verifying File Creation (Inside the Container):# ls -l Lists directory contents, showing example.org 32. Viewing File Contents (Inside the Container):# cat example.org Displays the contents of example.org created earlier. 33. Remember:# Replace [containerid] with the actual container ID in steps 13, 15, and 16. Use docker ps -a to view all containers, including stopped ones. Also published here.

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Docker Essentials: A Beginner's Guide to Containerization Commands

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