Chapter 13. How To

13.1. Graph a Single SNMP OID

When dealing with SNMP enabled devices, there are often times when you want to graph the value of a single OID.

This tutorial explains how to do this in Cacti. It also assumes that you have the "SNMP   Generic OID Template"

graph template, which is now included in Cacti as of version 0.8.5. If you do not see this template listed under Graph

Templates, download the template from the Cacti website in XML form and import it using the Import Templates menu

item.

To start the process of creating a new graph for your OID, click the New Graphs menu item and select the host that

contains the target OID from the dropdown. Under the Graph Templates box, you will see a dropdown on the last line

that reads (Select a graph type to create). From this dropdown, choose "SNMP   Generic OID Template" and click the

Create button at the bottom of the page.

You will be presented with several fields that will require input before the new graph can be created. They are de 

scribed in more detail below.

Table 13 1. Field Description: SNMP   Generic OID Template

Name

Description

(Graph) Title

The title that is to be used for the new graph. It is generally a good idea to keep

|host_description| in the title, as to make the graph easier to identify later.

(Graph) Vertical Label

The text that will be printed along the y axis of the graph. It is generally used to

describe units, such as 'bytes' or 'percent'.

(Graph Items) Legend Color The color that will be used to reprent the data on the graph.

(Graph Items) Legend Text

The text that will be used to describe the data on the graph legend.

(Data Source) Name

The title that is to be used for the new data source. It is generally a good idea to keep

|host_description| in the title, as to make the data source easier to identify later.

(Data Source) Maximum

The maximum value that will be accepted from the OID. Make sure you choose a value

Value [snmp_oid]

that is reasonable for the data you are trying to graph because anything larger than the

maximum will be ignored. If you are graphing a percentage, you should use '100' as

the value should never exceed this.

(Data Source) Data Source

How the data from the OID should be stored by RRDTool and interpreted on the

Type [snmp_oid]

graph. If the value of the OID represents the actual data, you should use GAUGE for

this field. If the OID value is a constantly incrimenting number, you should use

COUNTER for this field. The two remaining field values, DERIVE and ABSOLUTE can

be ignored in most situations.

(Custom Data) OID

The actual SNMP OID to graph. It is typically a good idea to enter the number OID

here as opposed to using MIB names. For instance, to get the number of open files on a

Netware server, you would use ".1.3.6.1.4.1.23.2.28.2.7.0" as the OID.

When finished filling in values for these fields, click the Create button. Your new graph can now be accessed through

the Graph Management page or the Graphs tab inside of Cacti.

13.2. Simplest Method of Going from Script to Graph (Walkthrough)

Written by Kevin der Kinderen, http://kdeuja.com/~kevin/

This HOWTO walks you through the simplest steps of graphing the output of a single value from a script. As a

new user of cacti, I had a difficult time understanding how to graph anything that wasn't canned with the original

load. After a lot of playing around, I came up with these procedures which can be built upon for more sophisticated

collections and graphs.

I do not use templates in this HOWTO. Templates provide a significant advantage if you are graphing the output for

multiple instances or creating graphs for multiple hosts. They help to maintain consistency and simplify setup.

The example here is not realistic, but can be used and expanded upon as a model for creating your own graphs.

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