Linux and operating systems

Time

17–24 weeks

Before this

Foundations of computer science

Leads to

Linux system administrator, Security engineer, DevOps engineer, SOC analyst

Anyone heading into security, DevOps or cloud. Most servers, security tools and attacks live on these systems.

1. Stage 1: The Linux command line , 3–4 weeks

   What to learn

   • Moving around the file system
   • Files, users and permissions
   • Pipes and redirection
   • grep, find, sed and awk
   • Installing software with a package manager

   Free resources

   • The Linux Command Line Book, William Shotts
   • OverTheWire: Bandit Practice, OverTheWire

   Build: Finish the first 20 levels of OverTheWire Bandit and keep notes on every command you learned.

   Move on when: You can do everyday work in a terminal without a mouse and read a man page to learn a new command.

2. Stage 2: How operating systems work , 4–6 weeks

   What to learn

   • Processes and threads
   • Memory and virtual memory
   • File systems
   • System calls
   • How a computer boots

   Free resources

   • Operating Systems: Three Easy Pieces Book, Remzi and Andrea Arpaci-Dusseau (University of Wisconsin)
   • The Missing Semester of Your CS Education Course, MIT

   Build: Write a tiny shell in C or Python that runs commands, supports pipes, and handles Ctrl+C.

   Move on when: You can explain what happens, step by step, when you run a program.

3. Stage 3: Running a Linux server , 4–6 weeks

   What to learn

   • Users, groups and sudo
   • Services with systemd
   • Logs and journalctl
   • SSH keys
   • Scheduled jobs and backups

   Free resources

   • Ubuntu Server documentation Docs, Canonical
   • ArchWiki Docs, Arch Linux community

   Build: Set up a Linux server in a virtual machine that serves a web page, logs in only with SSH keys, and backs itself up every night.

   Move on when: You can find out why a service failed from its logs and fix it.

4. Stage 4: Windows and PowerShell , 3–4 weeks

   What to learn

   • PowerShell basics
   • Windows services and the registry
   • Event logs
   • Active Directory: users, groups and domains
   • Group Policy

   Free resources

   • PowerShell documentation Docs, Microsoft
   • Active Directory Domain Services overview Docs, Microsoft

   Build: Build a small Windows lab with one domain controller and one client, and write a PowerShell script that lists every user and their last sign-in.

   Move on when: You can explain how a Windows domain sign-in works and where it is logged.

5. Stage 5: Scripting and hardening , 3–4 weeks

   What to learn

   • Bash scripting
   • Automating tasks with Python
   • Firewalls on the host
   • CIS Benchmarks
   • Auditing a system for weak settings

   Free resources

   • CIS Benchmarks Docs, Center for Internet Security
   • Lynis Tool, CISOfy

   Build: Audit your server with Lynis, fix the most important findings, and write a script that checks they stay fixed.

   Move on when: You can harden a fresh server and prove what you changed.

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