ced4568andClaude Sonnet 5
e007bcf000
Adds all 6 ROOT 02 modules (Linux system administration, storage & filesystems, the Networking Mental Model, Linux network inspection, DNS & HTTP, Linux troubleshooting) — 37 activities, each with a real lesson, demonstration/guided exercise, knowledge check, hands-on Lab, and reflection. The Networking Mental Model module (M3) gets deliberately extra depth per its "critical module" designation, with no lab by design — conceptual mastery via knowledge check and guided exercise, matching root-05-m00's own precedent. Adds 6 new hands-on Linux/networking scenarios plus 2 MCQs: linux-service-inspection (inspects the platform's own real nginx without touching it — a genuinely safe, real service-inspection target that avoids ever risking the Lab's own connectivity), linux-service-lifecycle (start/ verify/stop a fully controllable service), linux-storage-inspection, linux-network-inspection (ip/ss/getent/curl, each framed as answering one specific diagnostic question), linux-dns-http-diagnosis (a genuine DNS-resolves-but-wrong-port failure, diagnosed and fixed), and linux-troubleshooting-framework (a real missing-config-file failure, resolved via the RootNode Observe/Evidence/Hypothesis/Test/Repair/Validate/Prevent framework). All tested end-to-end via the real scenario-validation API, including negative tests confirming they fail when unsolved. Wires rootnode-linux-networking-assessment (2 required + 4 random-draw scenarios) using the existing Phase 3B assessment engine. Co-Authored-By: Claude Sonnet 5 <[email protected]>
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Demonstration: Three Failures That Sound Similar But Aren't
OBSERVE
All three of these LOOK like "it didn't work" — but each one rules out and rules in completely different layers.
$ curl http://this-name-does-not-resolve.invalid/
curl: (6) Could not resolve host: this-name-does-not-resolve.invalid
HYPOTHESIS
Which layer does THIS failure point at — DNS, routing, the port, or the application itself?
INSPECT
"Could not resolve host" happens BEFORE any network connection is even attempted — it's purely a DNS failure. No IP was ever found to connect to.
CHANGE
Now a different failure, against a name that DOES resolve:
$ curl http://localhost:9999/
curl: (7) Failed to connect to localhost port 9999: Connection refused
DNS/name resolution already succeeded here (localhost always resolves). "Connection refused"
means a TCP packet reached the destination and was ACTIVELY rejected — almost always because
nothing is listening on that port.
VERIFY
A third signature, distinct from both:
$ curl http://10.255.255.1:80/
curl: (28) Failed to connect to 10.255.255.1 port 80: Connection timed out
No response at all, not even a rejection — usually means the destination is unreachable (no route, or blocked silently), not that something is running but declining you.
Instructor Notes
Demo goal: Get students to viscerally distinguish these three error MESSAGES as three different diagnostic starting points, not interchangeable "it's broken" signals.
Approximate timing: 10 minutes live.
Common mistake to watch for: treating every connection failure as "the network is down" — each of these three messages should immediately narrow which layer to investigate next, per Module 5's troubleshooting exercise.