Diagnose a fault you did not choose, one method step at a time

short · 50 min · Objective 4.1

Task

Have a fault injected into lin-b's web service without knowing which one, then work it through the troubleshooting method in order -- identify, theorise, test, plan, implement, verify, document -- writing each step down as you go, with the time. The record is the product: it shows whether you reached the cause by method or by luck.

Steps

  1. Inject the fault: run the chosen line from injected.txt with bash lab/method/injected.txt, without reading it.
  2. Identify the problem: from the client, describe the exact symptom, and on lin-b gather the service status, recent log lines and recent changes. Write them under a heading ## 1 identify in lab/method/record.md, with the time.
  3. Write ## 2 theory with at least two possible causes, simplest first, then ## 3 test with the command that confirmed or ruled out each.
  4. Write ## 4 plan with the fix and its rollback, then carry it out and write ## 5 implement.
  5. Write ## 6 verify with the client-side check that shows the service works, and ## 7 document with the cause in one line beginning cause:.
  6. Only now read lab/method/injected.txt and record in lab/method/match.txt whether your cause line matches it.

Verify

These checks run in a POSIX shell: Terminal on macOS or Linux, and on Windows Git Bash (it comes with Git for Windows) or WSL. A stock Windows PowerShell or Command Prompt has no awk or grep, so there the first line fails.

grep -Ec '^## [1-7] (identify|theory|test|plan|implement|verify|document)' lab/method/record.md
grep -E '^## [1-7] ' lab/method/record.md | awk '{print $2}' | paste -sd' ' -
grep -c '^cause:' lab/method/record.md
grep -Eic 'match|yes|correct' lab/method/match.txt
wc -l < lab/method/faults.txt

All seven steps are present and in order 1 to 7, there is exactly one cause line, and it matches the injected fault. Repeat the lab with a different random fault until you have diagnosed three; a record that jumps from identify straight to implement is the habit the exam's scenario questions are designed to catch.

Notes

Time the first and last entries. How long identification took compared with the fix itself is usually the most instructive number in the record: most time goes to finding the cause, which is why the method front-loads gathering information.

This is an independent study companion for CompTIA Server+ SK0-005 and is not produced by or endorsed by CompTIA.