Troubleshooting and Diagnostics
This domain tests a structured approach to macOS faults: define the symptom, isolate the layer, gather evidence, change one variable, and verify the fix. Expect questions on startup modes, logs, disk checks, crashes, and when to preserve data before repair.
Method and tools
Start with scope: one user or all users, one network or all networks, one app or the whole system. Safe mode loads a minimal system and can reveal login-item or third-party software issues. Recovery provides Disk Utility, reinstall, and startup security options. On Apple silicon, hold the power button at startup to reach startup options; Intel Macs use different key combinations. log show and Console inspect unified logs, sysdiagnose collects a diagnostic bundle, Activity Monitor shows resource use, and diskutil or Disk Utility First Aid checks volumes. spindump helps with hangs.
Worked example
An app crashes immediately for one user but works for another. Reasoning: the fault is likely per-user preferences, permissions, or a login item, not a system-wide binary failure. Launch the app in a new test account; if it works, inspect the original user’s app preferences and caches. Collect a crash report or sysdiagnose before deleting data, and avoid erasing the whole disk as a first step.
Traps
- Resetting NVRAM or SMC is not a universal fix and is not the Apple silicon procedure.
- Deleting caches can remove evidence and is not a diagnosis.
- Safe mode is diagnostic, not a permanent configuration.
- Always verify a backup before destructive repair steps.
- A single-user app failure usually does not justify a full system reinstall.