Networking / RFC

Checking HTTPS Certificate Expiration with PowerShell — Directly Using .NET SslStream

Use .NET TcpClient and SslStream from PowerShell to check the server certificate, expiration date, and remaining days of an HTTPS site.
2026.09.07
Networking / RFC
Linux / CLI / DevOps

Viewing JSON APIs on Ubuntu with curl + jq ― Extract Only the Required Fields in One Go

Combine curl and jq on Ubuntu to extract only the necessary fields from a JSON API response. We will use the GitHub public Repository API as an example.
2026.09.07
Linux / CLI / DevOps
VBA / Office

Extracting IDs, Emails, and IPs from Logs Using Only Excel — Using REGEXEXTRACT / REGEXREPLACE

Using REGEXEXTRACT / REGEXREPLACE in Microsoft 365 Excel to extract IDs and IPs from log strings and easily mask email addresses.
2026.09.07
VBA / Office
VBA / Office

What Does VBA DoEvents Actually Do? — Understanding Why Screens Freeze and How Event Processing Works

This article delves into why VBA's DoEvents can restore Excel's responsiveness, exploring event processing, reentrancy, and the differences from asynchronous processing. It is designed to prevent treating DoEvents as a universal asynchronous solution.
2026.09.07
VBA / Office
Networking / RFC

What Does an HTTPS Certificate Verify? — Viewing the Entry Point of a TLS Connection Through a Sequence Diagram

This article provides an in-depth, diagram-based explanation of what HTTPS server certificates are used to verify, covering TLS 1.3, certificate chains, service identity, and DNS name matching.
2026.09.07
Networking / RFC
Microsoft 365 / Azure

Where Are Microsoft Graph Access Tokens Used? — Organizing the Flow Up to API Calls with Diagrams

This article uses diagrams to explain where Microsoft Graph access tokens are acquired and how they are used as Bearer tokens, including the differences between delegated access and app-only access.
2026.09.06
Microsoft 365 / Azure
Linux / CLI / DevOps

What to Check When a Service Fails on Ubuntu — Tracing via systemctl and journalctl

Don't just stop at systemctl status when troubleshooting Ubuntu service failures. Follow a step-by-step investigation procedure through unit definitions, states, processes, and journals, preserving diagnostic info before restarting.
2026.09.06
Linux / CLI / DevOps
Microsoft 365 / Azure

Why Use TXT Records for Microsoft 365 Domain Verification? — Understanding the DNS Authentication Flow

When adding a custom domain in Microsoft 365, why does registering a TXT record prove domain management rights? We break this down based on the DNS workflow and current Microsoft Learn documentation.
2026.09.06
Microsoft 365 / Azure
AI & Machine Learning

Don’t Just sudo AI-Generated Commands — A 5-Step Pre-Execution Checklist

This guide outlines a 5-step checklist to verify the purpose, target, permissions, changes, and recovery methods before running Linux commands suggested by AI. Essential practical rules to read before typing sudo.
2026.09.06
AI & Machine Learning
PowerShell

Verifying If Two Files Are Truly Identical — Using SHA-256 in PowerShell

Calculate SHA-256 using PowerShell's Get-FileHash to check if two files have identical contents. Also explains differences from file sizes, behavior when a single character is changed, and verification against distribution hashes.
2026.09.06
PowerShell
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