Lab 4 — OS & Networking: Trace, Debug, and Read the Substrate

[Nik-ari-ai]

Goal

Use ss, dig, tcpdump, curl -v, and journalctl to understand what happens when a POST /notes flies across the network into QuickNotes.

Changes

• submissions/lab4.md — Task 1 (packet trace + 5 debug commands + 502 reflection), Task 2 (outside-in debug + blameless postmortem), Bonus (TLS 1.3 handshake decode)
• submissions/lab4-trace.txt — tcpdump capture of one POST /notes

Testing

• Real tcpdump capture on lo: TCP handshake, POST /notes, 201 Created, FIN close
• Broken deploy reproduced (bind: address already in use), chain walked, repaired
• TLS proxy handshake captured and decoded (ClientHello/ServerHello/cert chain, TLS 1.3)

Checklist

• Title is a clear sentence (≤ 70 chars)
• Commits are signed (git log --show-signature)
• submissions/lab4.md updated