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📝 Block A Exam — Intuition#

"A → B transition signal: can you narrow down why a service won't come up, in three commands, without opening the docs?"

Gate: End of Block A (after A6, before B1) · Prerequisite: A1–A6 acceptance criteria passed

ℹ️ Run all bash labs/... commands from the 22-Learning-Path/ root (same path as the acceptance criteria in the modules).

This exam doesn't teach a new topic; it's proof of what you've learned. It has two parts: written concept questions and a hands-on applied task. The criterion isn't "I know it" — it's whether the command runs, the output is correct, and you can write your reasoning. Every question traces back to a module's acceptance criterion (right-hand column); this exam doesn't invent a new criterion, it gathers the existing acceptance criteria into a single session.

📌 How to take it: Close the module documents. Write/run the answers first, then compare against your own module. A copied answer won't get you into B — in B1 you'll be alone in front of a real broken system.

1️⃣ Concept questions (written)#

Write each one in your own words. The "correct" answer is in the module; write yours first.

# Question Traceability (module → acceptance criterion)
1 Explain the 640 permission in octal and rwx form; what can each of the three classes (owner/group/others) do? Tie this to the "least privilege" principle. A1 → permission + user/group criterion
2 What are the two different meanings of "disk full" (df -h vs df -i)? Which one is inode exhaustion? A1 → df -h/df -i criterion
3 What's the difference between "connection refused" and "connection timed out"? What does each point to, and at which layer? A2 → refused/timeout criterion
4 Why is a service listening on 127.0.0.1:80 "unreachable from outside"? What's the difference with 0.0.0.0? A2 → 127.0.0.1/0.0.0.0 criterion
5 What do the HTTP status code classes (2xx/3xx/4xx/5xx) tell you? Whose responsibility is 4xx versus 5xx? A3 → status code criterion
6 For a TLS certificate, what does each of expired / name-mismatch / chain errors mean? A3 → certificate criterion
7 Why does the "never rebase shared history" golden rule exist? How does history differ between merge and rebase? A4 → merge/rebase criterion
8 What does each of the three flags in set -euo pipefail prevent, individually? Give one example for each. A5 → set -euo pipefail criterion

Passing: Write at least 7 of the 8 questions, without looking at the module, technically correct and in your own words. Not a memorized definition — an answer with a why.

2️⃣ Applied task — "the service that won't come up"#

This task combines A1–A6 into a single scenario and is the A→B signal itself.

Task A — Diagnose the broken service (core): Solve the K00 — systemd won't come up broken lab. README.md only gives the symptom; you'll find the cause.

  • bash labs/broken/K00-systemd-ayaga-kalkmiyor/verify.sh passes with zero errors
  • You wrote the root cause and the diagnostic flow (symptom → narrowing → root cause → fix → verification)
  • You used at most hint-1/hint-2; if you opened hint-3/solution.md, this doesn't count as a pass this time

Task B — Prove the manual deploy is up: Use the A6/L06 setup.

  • systemctl is-enabled app → enabled and systemctl is-active app → active
  • curl -s http://127.0.0.1/health returns 200 + the expected body via nginx
  • You showed that in ss -tlnp output, app listens only on 127.0.0.1, nginx on 0.0.0.0:80

Task C — Layer narrowing (timed): Write the first three commands you used while finding the fault in Task A, and why each one came in that order. Soft target (not mandatory): time yourself and get to the right layer in a few minutes without opening docs — not speed, the right order matters.

🚫 Don't lose this exam to yourself#

Anti-pattern Why it's bad Right
Opening solution.md to "solve" K00 You never exercised your diagnostic muscle Start from the symptom, open hints gradually
Saying "I got it" and moving on Subjective; it won't hold up in B1 Show command output + written reasoning
Silencing a permission problem with chmod 777 Hides the problem, breaks least privilege Grant only the single missing bit
Guessing "it's DNS" No evidence; the exact opposite of Block B Show which layer it is with dig/ss/curl
Skipping Task C Narrowing discipline is the actual thing being measured Write the three commands and the reasoning for their order

✅ Did you pass?#

If all three are true, you're ready for Block B: - [ ] Concept: at least 7 of 8 correct + reasoned - [ ] Application: K00 verify.sh green (hints ≤2) and A6 reboot-safe proof - [ ] Narrowing: you narrowed a fault down to the right layer with three commands, without opening docs

If you didn't pass, there's nothing to be ashamed of — go back to whichever module the question/task you got stuck on belongs to. E.g., if you couldn't find the layer in Task A, go to A2; if you got stuck on TLS, go to A3. The exam isn't here to send you back, it's here to tell you where to go back to.

⏭️ Up next#

If you passed: B1 — Reading Logs. If you didn't pass: go back to the module you got stuck on, pass the acceptance criteria again.

"If you can't narrow down why a service isn't working in three commands, making it observable (Block B) is premature."