Linux Systemd & Service Errors: Failed to start, Unit not found, dependency cycles
Working reference for the 10 most common Linux systemd service errors. Failed to start (with journalctl -xeu diagnosis), Unit not found (daemon-reload after custom-unit drop), control process exited non-zero, Start request repeated too quickly (StartLimitBurst), Dependency cycle, Unit is masked, bad ExecStart values, false 'running' status without health checks, permission denied on low ports (CAP_NET_BIND_SERVICE), daemon-reload required after edits. Cross-links to the User & Service Management command reference.