Monitorix is a free, Open Source monitoring tool that can be used to monitor as many services and system resources as possible. Unlike other monitoring tools, it is very simple to install, configure and monitor the systems. Initially, it was developed to support only the RPM based systems such as Red Hat, CentOS etc., but, later it is expanded its support to other distributions like Debian/Ubuntu, and BSD systems such as FreeBSD, NetBSD, and OpenBSD.
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Monitorix – An Open Source, Lightweight System Monitoring Tool For Linux (Unixmen)