System Monitoring

Be Proactive!

Don't you want to take a proactive stance and always know the current status of all your network servers, devices and resources?

Wouldn't it be better to be able to predict issues and possibly fix them before they affect your users - thereby keeping your reputation as a system administrator?

Well, that is partly what system monitoring is all about - Helping to keep you on top of the current status all of your systems and servers.

In addition to giving you tools to help you be more proactive in the short term, network monitors can also log and graph many aspects of your systems and servers, providing you with a visual history. This can be very useful for long-term planning for things like file storage, memory, or bandwidth upgrades.

This type of history can also aid in troubleshooting issues such as network bandwidth or CPU utilization increases that seem to occur during certain times of the day.

Types of Network Monitoring Tools

There are MANY network monitoring systems available. What you choose depends on the type of monitoring you are looking for. Some monitoring tools simply poll devices or servers and graph the data collected, while others not only have the ability to graph much of your systems' information, but they can also send email or SMS alerts when certain conditions are met or thresholds are passed.

At Reverse Polarity LLC, we have been installing and supporting several open-source network monitoring tools for over ten years now. In many cases, a combination of passive graphing and active monitoring solutions turns out to be a good fit for many of our clients.

For example, we often combine a graphing tool such as MRTG or Cacti to simply graph the network traffic/bandwidth at key points in a network, along side an network monitor and alerting solution such as Xymon to monitor all aspects of our clients' servers and to send alerts when necessary.

Open-Source Monitoring Tools We Support

Below is a partial list of the open-source network monitoring tools that we install and support. Take a look at each of them and see if they might be a good fit your network environment to help you gain a proactive stance against unknown server and network problems.


Xymon (pronounced just like "Simon" and formerly known as "Hobbit Monitor") - is an open-source tool for monitoring servers, applications and networks. It collects information about the health of your computers, the applications running on them, and the network connectivity between them. All of this information is presented in a set of simple, intuitive web pages that are updated frequently to reflect changes in the status of your systems.

Xymon is capable of monitoring a vast set of network services, e.g. mail-servers, web-servers (both plain HTTP and encrypted HTTPS), local server application logs, resource utilization and much more.

Much of the information is processed and stored in RRD files, which then form the basis for providing trend graphs showing, for example:

  • CPU Load
  • Server memory usage
  • Drive space utilization
  • How webserver response-times vary over time
  • And much, much, more

Xymon's can easily be extended to monitor, graph and alert for just about anything thanks to its ability to run external, custom scripts. These scripts just need to return some information to Xymon in an acceptible format for Xymon to begin monitoring, and graphing the data.

As a matter of fact, Bill Arlofski (Reverse Polarity LLC) has written a custom Xymon server-side script to monitor temperature readings from a ControlByWeb 4-temperature/2-relay temperature module. Take a look HERE to see it!

For more information about Xymon take a look at the Xymon's web page on Sourceforge

The easiest way to understand what Xymon does is to see it in action. Click HERE to see a live view of Xymon monitoring its author's home network.


MRTG monitors and graphs your network traffic. The Multi Router Traffic Grapher is an open-source tool that polls your network routers and switches via SNMP and gathers information regarding packets sent and received. The data is then graphed and presented to you on HTML pages. MRTG is capable of monitoring and graphing much more than switches and routers, and can be used to monitor just about anything including disk space, system load, temperature etc by using external scripts.


Cacti is another open-source network graphing tool that is easily configured via an intuitive web interface. It allows you to graph statistics of your network devices and servers via SNMP (Simple Network Management Protocol), or from data collected from plug-in scripts.

Cacti also includes a "User Management" feature which allows you to manage who can see which graphs, or who has access to configure Cacti.


Wireshark is an open-source network packet capturing tool and is also the world's foremost network protocol analyzer. We use Wireshark to sample our clients' network traffic and to help us pinpoint where problems might be occurring. Problems such as machines infected with viruses, or other malware are often quickly and easily isolated with a tool such as Wireshark.


Snort - Intrusion Detection System. The Snort website describes Snort as an open source network intrusion detection system, capable of performing real-time traffic analysis and packet logging on IP networks. It can perform protocol analysis, content searching/matching and can be used to detect a variety of attacks and probes, such as buffer overflows, stealth port scans, CGI attacks, SMB probes, OS fingerprinting attempts, and much more.


Awstats is an advanced open-source web log analyzer and statistics utility that generates easy to read, informative, graphical representation of site hits, visits, bandwidth and more!