Nagios is a popular open source monitoring solution that could monitor and report alerts of several components of an IT infrastructure including Windows and of course Linux machines. Basically Nagios can monitor:
- System resources (e.g. CPU load, disk usage, etc)
- Network services
- Environmental parameters (e.g. temperature probes)
In the more general case, Nagios can monitor every piece of collectible information (if a plug-in to collect that information has been written, else it is always possible to write your own plug-ins). The solution can also work on secured links (SSH...) and has a Web interface (V-Shell) through the system administrator can interact if he do not wish to use the command line.