id: 112C
title: Troubleshooting.
date: 2025-01-18

Troubleshooting.

Nine rules of debugging are:rW6

  1. Understand the system: read about it, learn its tools.
  2. Make it fail: identify success and failure cases, look for patterns in intermittent failures, record all of the steps.
  3. Quit thinking and look: only guessing should be about where to add more visibility.
  4. Divide and conquer: cut down the problem space progressively, zooming into the cause.
  5. Change one thing at a time: don’t fix until the cause is clear, try comparing the current state to the last known good state.
  6. Keep and audit trail: write all changes down, assess for cause and effect.
  7. Check the plug: start at the beginning, identify and verify all assumptions.
  8. Get a fresh view: rubber duck, talk to experts, listen to experience, discuss symptoms rather than conclusions.
  9. If you didn’t fix it, it ain’t fixed: verify fixes truly work, know that things can’t just start working, find the root causes.
  1. ↩

    David Wheeler, “David A. Wheeler’s Review of ‘Debugging’ by David J. Agans,” March 2, 2004, https://dwheeler.com/essays/debugging-agans.html. (See notes.)