01. Inspect DNS records
The dig utility queries DNS servers and displays information about domain name resolution.
dig example.com A
dig example.com AAAA
dig example.com MX
dig +short example.comTechnical knowledge base
Simple notes.
Complex systems.
A compact collection of practical references for networking, infrastructure, and system administration. Useful commands, common concepts, and troubleshooting tips.
Topics
01 / NETWORKING
DNS Fundamentals
Domain resolution, record types, TTL values, caching, and troubleshooting name resolution.
02 / SECURITY
TLS & Certificates
Understanding HTTPS, certificate chains, automated renewal, and secure connections.
03 / PROTOCOLS
HTTP Essentials
Request methods, response codes, headers, redirects, and connection behavior.
04 / OPERATIONS
System Diagnostics
Essential command-line utilities for checking services, connectivity, and system health.
Quick Reference
02. Check an HTTPS endpoint
Use curl to inspect response headers, verify connectivity, and troubleshoot HTTP behavior.
curl -I https://example.com
curl -v https://example.com
curl -L https://example.com03. Inspect a TLS certificate
OpenSSL can display certificate information from a remote TLS-enabled service.
openssl s_client \
-connect example.com:443 \
-servername example.com \
</dev/null04. Check listening ports
List TCP listeners and identify processes bound to local network ports.
ss -ltnp
ss -tulpn
systemctl status caddyAbout System Notes
System Notes is a lightweight technical reference focused on practical infrastructure knowledge. The goal is to keep useful information concise, readable, and easy to revisit.
No accounts. No tracking. Just technical notes.