Small and medium-sized organizations require effective security monitoring but often face limitations in cost, infrastructure, and technical resources. This work introduces CyberSentinel, a modular security toolkit designed to detect and respond to common threats in Linux environments. The system combines six functions: network reconnaissance monitoring, system-log analysis, file-integrity checking, process and endpoint monitoring, firewall management, and intrusion detection. A Bash- based controller coordinates these functions and combines their results into a single security report, while a lightweight web interface presents the detected events in a readable form. The toolkit uses freely available security utilities, reducing the need for costly commercial security platforms. Evaluation was performed in a three-machine isolated laboratory using ten simulated attack scenarios. Detailed testing covered port-scan detection, firewall protection with automated IP blocking, and communication between the detection modules and dashboard. All ten test scenarios were identified successfully. Log monitoring and file-integrity checking provided particularly useful alerts after their detection thresholds were adjusted. The experimental results indicate that CyberSentinel offers a practical approach for basic threat monitoring and response where security resources are limited.

T.Yuvanraj, Dr.S.Nandhini, "CyberSentinel A Modular Linux-Native Threat Detection and Response Toolkit Using Open-Source Command-Line Tools" International Journal of Computer Science and Engineering Development, V1(4): Page(01-08) September - October 2026. ISSN: 3139-0862. www.ijcsed.com. Published by Scientific and Academic Research Publishing.