Linux: a Guide from the First Commands to System Administration

Linux is an open-source operating system kernel and the foundation of most servers, containers and cloud machines. For an administrator or DevOps engineer it is the everyday working environment: websites, databases, CI runners and Kubernetes nodes almost always run on Linux, and they are managed through the terminal.

This guide is a map of the topic. It collects the key concepts and the order in which they are easiest to learn. Each topic is covered in detail in a separate article.

What the topic consists of

• Basics — the kernel and distributions, the directory tree from the root /, system boot.
• Command line — navigation, files, packages, processes, search and text processing.
• Users and permissions — rwx, chmod, chown, sudo and the Permission denied error.
• Automation — bash scripts, variables, conditions, loops and cron.
• Services and logs — systemd, systemctl, journalctl.
• Networking and security — IP, DNS, ports, SSH, firewall.

Where to start

If Linux is new to you, start with the article on what Linux is: how the kernel differs from a distribution, where configuration files and logs live, and how the system boots. You can try everything safely in a virtual machine, WSL or a Docker container.

Next, keep the command cheat sheet at hand: it covers most of the daily work in the terminal. Then learn about permissions — this is the most common cause of errors for beginners, from a script that does not run to a 403 on a web server.

When the commands become familiar, move on to automation: your first bash script, error handling and scheduled runs with cron.

Key principles

• Everything is a file, and the whole tree starts at /.
• Work as an ordinary user, and use sudo for individual commands.
• Do not fix Permission denied with chmod 777 — give the right to the one who needs it.
• The answer to almost any question is in man, the logs and journalctl.
• If you repeat an action twice, write a script.

All the topics — from the file system to networking and security — are covered in practice in our Linux course.