dmwasielewski

Diagnostic Checks Reference

2 min read

Diagnostic Checks Reference

Summary

This note is a quick reminder of common diagnostic checks that support troubleshooting across systems and services.

Example first-pass sequence

When the issue is still unclear, a short sequence like this usually gives a better starting point than guessing:

# scope and context
whoami
hostnamectl
date
 
# service state
systemctl status SERVICE_NAME
 
# recent evidence
journalctl -u SERVICE_NAME -n 50 --no-pager
 
# network assumptions
ip addr
ip route
nslookup example.internal
curl -I http://HOST_OR_SERVICE

For Windows or Microsoft-heavy paths, keep the same structure:

Get-Date
whoami
Get-Service -Name Spooler
Get-WinEvent -LogName System -MaxEvents 20
Test-NetConnection -ComputerName HOSTNAME -Port 443

When to use this note

  • when you need a fast first-pass checklist before changing anything
  • when you want to narrow scope before diving into a domain-specific guide
  • when you know the problem category only loosely and need a structured starting point

Scope checks

CheckPurpose
affected user or host countdecide whether issue is isolated or broad
compare working vs failing casenarrow scope fast
recent change awarenesscheck whether something changed before the symptom

System and service checks

CheckPurpose
service statusconfirm whether service is running
recent logsadd evidence and timing
config statecheck whether expected settings are present

Minimum evidence set

Before changing anything, try to collect at least:

  • what is failing
  • who or what is affected
  • when it started
  • one service-state check
  • one log or event check
  • one path or connectivity check if network is involved

Network and path checks

CheckPurpose
IP and route stateconfirm basic path assumptions
DNS resolutionseparate name issues from connectivity
port or app reachabilitydistinguish service issue from path issue

Notes

  • this note is intentionally broad and lightweight
  • the point is to support structured thinking, not replace domain-specific commands
  • detailed commands still belong in Linux, Networking, Security, or Microsoft sections where appropriate
  • a good first-pass diagnostic note should still include a few repeatable commands, not only abstract reminders

Common mistakes

  • skipping scope checks and going straight to fixes
  • assuming one successful test proves the full path is healthy
  • collecting too little evidence before changing configuration

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