17. Monit
Monit is a small Open Source utility for managing and monitoring a single Unix system. Monit conducts automatic maintenance and repair and can execute meaningful causal actions in error situations.
The non free M/Monit allows to manage all your Monit servers. M/Monit expand on Monit’s capabilities and provides monitoring and management of all your Monit enabled hosts via a modern, clean and well designed user interface which also works on mobile devices.
18. MRTG
The Multi Router Traffic Grapher, or MRTG is being used to graph and monitor SNMP network devices and draw pretty pictures showing how much traffic has passed through each interface. MRTG is written in perl and works on Unix/Linux as well as Windows and even Netware systems.
MRTG uses the Simple Network Management Protocol (SNMP) to send requests with two object identifiers (OIDs) to a device. The device, which must be SNMP-enabled, will have a management information base (MIB) to look up the OIDs specified.
After collecting the information it will send back the raw data encapsulated in an SNMP protocol. MRTG records this data in a log on the client along with previously recorded data for the device. The software then creates an HTML document from the logs, containing a list of graphs detailing traffic for the selected devices in the server.
19. Munin
Munin the monitoring tool surveys all your computers and remembers what it saw. It presents all the information in graphs through a web interface. Its emphasis is on plug and play capabilities. After completing a installation a high number of monitoring plugins will be playing with no more effort.
Using Munin you can easily monitor the performance of your computers, networks, SANs, applications, weather measurements and whatever comes to mind. It makes it easy to determine “what’s different today” when a performance problem crops up. It makes it easy to see how you’re doing capacity-wise on any resources.
Munin uses the excellent ​RRDTool (written by Tobi Oetiker) and the framework is written in Perl, while plugins may be written in any language.
Munin Installation and Configuration Guide
https://munin-monitoring.org
20. Nagios Core
Nagios offers monitoring and alerting services for servers, switches, applications, and services. It alerts the users when things go wrong and alerts them a second time when the problem has been resolved.
NRPE Nagios Remote Plugin Executor (NRPE) is a Nagios agent that allows remote system monitoring using scripts that are hosted on the remote systems. It allows for monitoring of resources such as disk usage, system load or the number of users currently logged in. Nagios periodically polls the agent on remote system using the check_nrpe plugin.
