Use dig to compare authoritative DNS records with public resolver cache after DNS changes.
Use journalctl to Debug a Failed systemd Service
When a Linux service fails under systemd, the fastest first move is usually not digging through random files in /var/log. Ask systemd what happened, then
Debug HTTP Redirects and Timing with curl
Use curl to follow redirects, inspect the final URL, measure DNS/TLS/TTFB timing, and spot redirect loops or slow origin responses.
Testing Memory Allocation
This nice routine is for testing PHP’s memory limits by increasingly allocating 50 more megabytes at a time. Each pass is setting the memory limit with an
