Graph Any Data with Cacti!

Shawn Powers — Thu, 27 Apr 2017 11:51:16 +0000

For the past few years, I've been trying to understand how to make graphs using RRDtool (Round-Robin Database tool) after failing miserably to understand MRTG (Multi-Router Traffic Grapher) before that. The thing I like about RRDtool is that it's newer and supports a wider variety of data sources. It's still incredibly complicated though, and I've given up on learning how to use it on multiple occasions. That's when I discovered Cacti.

Cacti is not a new program. It's been around for a long time, and in its own way, it's a complicated beast itself. I finally really took the time to figure it out, however, and I realized that it's not too difficult to use. The cool part is that Cacti makes RRDtool manipulation incredibly convenient. It did take me the better part of a day to understand Cacti fully, so hopefully this article will save you some time.

The Goal

I want to create a graph that graphs something automatically and does it using a bash script as the input as opposed to SNMP or anything like that. I've been using bash for years, and I'm comfortable using the command line to procure data. In fact, for this project, I'm going to adapt a script I use for BirdTopia (my continual birdcam project for the past few years) that will pull a temperature from the command line. I want to pull the temperature from two different cities and graph them together. For this example, I use Petoskey, Michigan (where I live), and Houston, Texas (where Linux Journal headquarters are located).

Here's the script:


#!/bin/bash
curl -s "http://api.wunderground.com/weatherstation/
 ↪WXCurrentObXML.asp?ID=$1" \
| grep temp_f | sed 's/.//' | sed 's/.//' | sed
 ↪'s///' | sed 's/<\/temp_f>//'

It looks complex, but really it just downloads the API information from Weather Underground for the weather station given as an argument, and then uses sed (stream editor) to pare down the information to a simple number—specifically, the numerical degrees in Fahrenheit. If you prefer Celsius, I applaud your country for adopting the metric system, but sadly, my brain just can't relate Celsius to how warm the outdoor temperature feels.

One tricky part is figuring out what the proper weather station ID is for your city. I wish you could just use a ZIP code, but I've been unable to find a command-line weather API that will take a ZIP code. So if you're following along, just head over to Wunderground and load the page for your locale. Once there, click on the link shown in Figure 1 (your text will be different, but the location on the page should match). The next page will show the name of your local weather station. You can see mine in Figure 2.

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Graphing

Graph Any Data with Cacti!

The Goal