What is Munin?
Munin is a networked resource monitoring tool that can help analyze resource trends and "what just happened to kill our performance?" problems. It is designed to be very plug and play. A default installation provides a lot of graphs with almost no work.
In Norse mythology Hugin and Munin are the ravens of the god king Odin. They flew all over Midgard for him, seeing and remembering, and later telling him. "Munin" means "memory".
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Complicated does not mean efficient ; easy isn't superficial.
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Easy to install
Follow the instructions and install & configure munin in less than 10 minutes
Real-time alerts
Munin polls your servers once every 5 minutes. Don't wait any longer to be notified when something goes wrong
Scalable
Monitor all-scales installations, from your home Raspberry Pi up to a 100 nodes cluster
Flexible
Munin will cleverly choose from 500 available plugins to monitor every service running on your server
Extensible
Write your own plugins in the language of your choice to supervise whatever you want
Maintained
Munin's first version was released in 2002 and it has kept evolving since
How does it work?
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 an 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 has a master/node architecture in which the master connects to all the nodes at regular intervals and asks them for data. It then stores the data in RRD files, and (if needed) updates the graphs. One of the main goals has been ease of creating new plugins (graphs).
Plugins
Plugins are small, standalone executables. They are easy to write, and can be written in any language. You can find many user contributed plugins in the contrib repository or easily write your own ones.
Read more on Munin Guide