Linux & service basics: logs, systemd/PM2, permissions, Nginx reverse proxy, DNS checks

PURPOSE

Diagnoses common Linux service issues using logs, systemd/PM2, file permissions, Nginx reverse proxy checks, and DNS sanity checks.

WHEN TO USE

• TRIGGERS:
  • Show me why this service is failing using logs, then give the exact fix commands.
  • Restart this app cleanly and confirm it is listening on the right port.
  • Fix the permissions on this folder so the service can read and write safely.
  • Set up Nginx reverse proxy for this port and verify DNS and TLS are sane.
  • Create a systemd service for this script and make it survive reboots.
• DO NOT USE WHEN…
  • You need kernel debugging or deep performance profiling.
  • You want to exploit systems or bypass access controls.

INPUTS

• REQUIRED:
  • Service type: systemd unit name or PM2 process name.