Linux & DevOps Troubleshooting Blog
Practical guides for Linux engineers — NGINX debugging, process troubleshooting, CIS hardening, and production incident response.
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79 posts · page 1 of 9
NGINX 502 Bad Gateway Under Load: Root Causes and Fixes
NGINX 502 errors under load are almost never a simple app crash. This guide covers the real root causes — connection backlog overflow, keepalive misconfiguration, ephemeral port exhaustion — with diagnostic commands and config fixes from production incidents.
Log Analysis for Security Investigations: Windows Event Logs and Web Server Access Logs
A practical guide to log analysis for security investigations — Windows Event Viewer, critical Event IDs, Apache access log parsing, and the Linux command-line tools that make manual log analysis fast and effective.
Diamond Model of Intrusion Analysis: 4 Core Components Explained (2026)
A technical breakdown of the Diamond Model of Intrusion Analysis — adversary, victim, capability, and infrastructure — with real attack examples, meta-features, and how it compares to the Cyber Kill Chain and MITRE ATT&CK.
Cyber Kill Chain: All 7 Phases Explained with Real Attack Examples (2026)
A technical deep-dive into the Cyber Kill Chain — all 7 phases mapped with real attacker techniques, detection indicators, and defensive controls. Includes a full real-world attack walkthrough and Kill Chain vs MITRE ATT&CK comparison.
How to Trace Route in Linux: traceroute Examples
Use traceroute in Linux to diagnose network path issues — read hop output, interpret timeouts, use TCP mode to bypass firewalls, and identify where packets are being dropped.
Too Many Open Files Linux: Fix Guide
Fix 'too many open files' errors on Linux — increase file descriptor limits for processes and system-wide, diagnose FD leaks, and configure permanent limits for production services.
How to Test TCP Connection in Linux: nc, curl, telnet
Test TCP connections in Linux using nc, curl, telnet, and /dev/tcp — verify port reachability, measure response time, and debug connection failures with real examples.
systemctl Service Not Starting: Complete Fix Guide
Fix systemctl service not starting — diagnose failed units, read exit codes, resolve dependency errors, and fix the most common reasons a Linux service won't start.
systemctl Restart Service Not Working: Fix Guide
Fix systemctl restart not working — diagnose failed units, read journal logs, handle dependency failures, and resolve the most common systemd service restart failures.