📚 Learning and exploring Linux.

This repository is for me to explore Linux. That's a wide scope of technology! Because I develop on macOS, I need a test bed for exploring Linux. I'll do this by exploring Linux in a Docker container by way of remote development in VS Code using a "Dev Container".

I'll choose the Debian Linux distribution to experiment with for two reasons. First, it's a common distribution to build containerized workloads like web servers on top of, and I've used it for many of my own workloads. Secondly, Debian is in the middle of the spectrum between small distributions like Arch and large distributions that can be used on the desktop like Ubuntu. It seems like an effective representative.

There are some miscellaneous things I'd like to learn about Linux (or even more broadly Unix-based systems and computing tools) like SSH (again, not a Linux-specific thing), systemd, file permissions, Unix domain sockets, and more.

NOTE:

This was developed on macOS and for my own personal use.

Follow these instructions to follow along with the learning journey presented by this codebase.

1. Start Docker
   • You should have Docker Desktop (or an alternative, like Colima) installed and running.
2. Open this project in VS Code
3. Attach VS Code to the dev container
   • VS Code will prompt you with a notification to reopen the project in a dev container. Click the "Reopen in Container" button.
4. Show the Debian version
   • Issue the following command in the VS Code integrated terminal.

   • lsb_release -a

   • Altogether, it should look like this.

   • vscode ➜ /workspaces/linux-playground $ lsb_release -a
     No LSB modules are available.
     Distributor ID: Debian
     Description:    Debian GNU/Linux 12 (bookworm)
     Release:        12
     Codename:       bookworm
     

   • Or, look at the version in the /etc/debian_version file. It should look like this.

   • vscode ➜ /workspaces/linux-playground $ cat /etc/debian_version 
     12.11
     

5. Start a Docker container

   • ./ssh-container-start.sh

   • This is a "Docker-in-Docker" scenario. We are going to use this container to explore SSH.
6. Check the status of the container

   • docker container ls

   • This is a command you will use frequently to see what containers are up, what ports are forwarded, what are the IDs of the containers, etc. You might know about the older command that does the same thing: docker ps.
7. Attach to the container

   • ./ssh-container-attach.sh

   • Start experimenting. When you want to detach from this container and return to the dev container, you need to type a special string of characters. Read the detailed note in ssh-container-attach.sh. Now, you have a substantial two-system Linux development and exploration environment that you can freely explore!
8. Restart the SSH service in the container
   • For some reason, the SSH service needs to be restarted. If I don't restart it then I have trouble ssh'ing into the container and I get a kex_exchange_identification: read: Connection reset by peer error. Use the following command to restart the SSH server (root is needed).

   • docker exec --user root ssh-server service ssh restart

9. SSH into the container

   • ssh -o StrictHostKeyChecking=accept-new -p 2345 myuser@localhost

   • It will prompt you for a password. Refer to the Dockerfile and to the note about the "bootstrap" design problem. Think about this design problem. Are the ergonomics of Dockerfiles awkward? Yes, in my opinion, they are. This is, in part, just the nature of Unix/Linux, the overall ecosystem, distributed computing, and security schemes.
   • Success, you are in a shell session in the container thanks to SSH!

I have to continually learn and re-learn the basics of SSH because I don't use it frequently. I don't do much system administration type work. It's tedious to relearn the basics from scratch so I would prefer to encode some knowledge in this notes section and in the runnable examples in this codebase.

General clean ups, TODOs and things I wish to implement for this project:

• DONE Start an SSH server. Connect to it from another container. Connect to it from my Mac host.

  • DONE start another container. I got that working but it's slow because it has to download the whole image but that's strange because I already have the image locally because it's the same one powering the dev container. I think I want to try a side-car "dev container"? UPDATE: no you can't do multi-container stuff without Docker Compose and I'm not interested in coupling my dev workflow to VS Code + Dev Containers + Docker Compose. That's too hat on hat. I'm going to do Docker-in-Docker (which is also a little hat-on-hat but at least I get control back). UPDATE: ok this works but there's an interesting snag with attaching/detaching from the container. A workaround is detailed in the ssh-container-attach.sh script.
  • DONE Maybe use password-based authentication? Public/private key would be better.
  • DONE (install openssh-server with apt) Debian (at least the Docker container) is pre-installed with ssh - OpenSSH remote login client. How should I install SSH server software?
  • SKIP Configure key-based authentication. Use ssh-copy-id.

• DONE (I installed the OpenSSH server) Install a package, or series of packages using the package manager(what is it apt-get? I always get them confused). UPDATE: Ok I read some docs and I was interesting in using tasksel or aptitude because are the highest level interactive tools for package management but they were not installed on the system. This was a little surprising. I would be curious to know more about these tools; are they effectively never used by the community? I'll just stick to apt which is for interactive usage. Contrast this with apt-get which is for scripts. So I tried apt update to make sure my copy of the list of packages and then apt search openssh which revealed many things, including

  openssh-server/stable 1:8.4p1-5+deb11u1 arm64 secure shell (SSH) server, for secure access from remote machines

• Consider unbundling some of the demo from VSCode/DevContainers/SSH/Linux. I think want to root the VSCode and DevContainers stuff in my vscode-playground. My interest in SSH right now is mostly in the context of remote dev environment so not sure there is enough content for linux-playground or an ssh-playground (definitely not).

• Debian Wiki: SSH
• Debian Manual: The Debian GNU/Linux FAQ ... Chapter 8. The Debian package management tools
• Debian Manual: Debian Reference ... Chapter 2. Debian package management