Chapter 9. Data Input Methods

Name

Description

Update RRD File (Output

Check this box if you want Cacti to insert the return value from this field into the RRD

Only)

file. Obviously, this box needs to be checked for at least one output field per data input

source, but can be left blank to have Cacti store the value in the database instead.

When you are finished filling in all necessary fields, click the Create button to continue. You will be redirected back

to the data input method edit page. From here you can continue to add additional fields, or click Save on this screen

when finished.

9.2. Making Your Scripts Work With Cacti

The simplest way to extend Cacti's data gathering functionality is through external scripts. Cacti comes with a number

of scripts out of the box which are located in the

scripts/

directory. These scripts are used by the data input methods

that are present in a new installation of Cacti.

To have Cacti call an external script to gather data you must create a new data input method, making sure to specify

Script/Command for the Input Type field. See the previous section, Creating a Data Input Method

1

for more information

about how to create a data input method. To gather data using your data input method, Cacti simply executes the

shell command specified in the Input String field. Because of this, you can have Cacti run any shell command or call

any script which can be written in almost any language.

What Cacti is concerned with is the output of the script. When you define your data input method, you are required to

define one or more output fields. The number of output fields that you define here is important to your script's output.

For a data input method with only one output field, your script should output its value in the following format:

<

value_1

>

So if I wrote a script that outputs the number of running processes, its output might look like the following:

Example 9 1. Example script output using 1 field

67

Data input methods with more than one output field are handled a bit differently when writing scripts. Scripts that

output more than one value should be formatted like the following:

<

fieldname_1

>

:

<

value_1

> <

fieldname_2

>

:

<

value_2

>

...

<

fieldname_n

>

:

<

value_n

>

Lets say that I write a script that outputs the 1, 5, and 10 minute load average of a Unix machine. In Cacti, I name the

output fields '1min', '5min', and '10min', respectively. Based on these two things, the output of the script should look

like the following:

Example 9 2. Example script output using 3 fields

1min:0.40 5min:0.32 10min:0.01

One last thing to keep in mind when writing scripts for Cacti is that they will be executed as the user the data gatherer

runs as. Sometimes a script may work correctly when executed as root, but fails due to permissions problems when

executed as a less privileged user.

Notes

1. data_input_methods.html

15