LEARNz
A Learning is a course on one subject. The notes and howtos elsewhere on this site each answer one question; a Learning goes through a subject in order, with practice.
Every Learning is split into levels, and each level ends with a small check. There is no time limit: when you can do what the check asks, go on to the next level.
The Learnings
| Learning | Written | Levels | What you learn |
|---|---|---|---|
| SDD (Spec Driven Development) | 2026 | 6 | Working with a coding agent from a vague request to verified behavior: write a contract, plan one change, implement it and show the evidence. One small lab, walked first with Matt Pocock Skills as the baseline and then, if you like, with Spec Kit, OpenSpec, BMAD Method or Superpowers |
| Linux Namespaces | 2016-2017 (and 2026) | 5 | The isolation containers are built from, by hand: what each namespace separates, giving a process its own, connecting network namespaces with veth pairs, a bridge and Open vSwitch, and doing it without root through the user namespace |
| Linux Process Memory | 2017 | 3 | What the memory of a process is made of, how to read it from /proc, and what VSS, RSS, PSS and USS count |
| Xen on Debian 4 | 2007-2008 | 4 | Historical: a Xen host from the first dom0 in a virtual environment to a hardened physical server with a base image and service guests |
| Postfix Mail Server | 2007-2010 | 4 | Historical: from a basic installation over SASL and TLS to complete mail systems with filtering, delivery rules and reports |
How to read one
Start at the Learning's own page. It lists the levels, the articles in the order to read them, and what you need to set up.
Each Learning stands on its own. Its articles link to each other with Previous and Next, and back to the Learning's page.