ossec-hids

OSSEC is an open-source host-based intrusion detection system that integrates log monitoring, file integrity verification, rootkit detection, and real-time active response. It monitors systems to identify unauthorized activity, brute-force attacks, and configuration changes. It runs as a background service and command-line utility across servers and agent endpoints.

From the repository: “OSSEC is an Open Source Host-based Intrusion Detection System that performs log analysis, file integrity checking, policy monitoring, rootkit detection, real-time alerting and active response.”