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Data Input Methods

Data input methods allow Cacti to retrieve data to insert into data sources and ultimately put on a graph. There are different ways for Cacti to retrieve data, the most popular being through an external script or from SNMP.

Creating a Data Input Method

To create a new data input method, select the Data Input Methods option under the Management heading. Once on that screen, click Add on the right. You will be presented with a few fields to populate on the following screen.

Table 9-1. Field Description: Data Input Methods

Name Description
Name Give the data query a name that you will use to identify it. This name will be used throughout Cacti to identify the data input method.
Input Type Select the type of data input method you are trying to create. Valid options here are 'Script Command', 'SNMP', 'SNMP Query', and 'Script Query'.
Input String This field is only used when the Input Type is set to 'Script Command'. It specifies the full path to the script including any per data source variables inside <>'s from the user. For instance, if you are passing an IP address to a script, your input string might look something like: /usr/bin/perl /path/to/ <ip> When the user creates a data source based on this data input method, they will be prompted for an IP address to pass onto the script.
Output String This field is only here for legacy purposes and will probably go away in a future version of Cacti.

When you are finished filling in all necessary fields, click the Create button to continue. You will be redirected back to the same page, but this time with two new boxes, Input Fields and Output Fields. The Input Fields box is used to define any fields that require information from the user. Any input fields referenced to in the input string must be defined here. The Output Fields box is used to define each field that you expect back from the script. All data input methods must have at least one output field defined, but may have more for a script.

Data Input Fields

To define a new field, click Add next to the input or output field boxes. You will be presented with some or all of the fields below depending on whether you are adding an input or output field.

Table 9-2. Field Description: Data Input Fields

Name Description
Field/Field Name Either select or type in the name of the field you want to define. No spaces or other non-alphanumeric characters (except '-' or '_') should be used in this field.
Friendly Name Enter a more descriptive name for this field which will be used for identification throughout Cacti.
Regular Expression Match (Input Only) If you want to enforce a certain regular expression pattern when the user enters a value for this field, enter it here. The regular expression must follow POSIX syntax as it will be passed to PHP's ereg() function.
Allow Empty Input (Input Only) Select whether you want to allow the user to leave the value of this field blank or not.
Special Type Code (Input Only) Sometimes Cacti needs to reference a field internally, but needs to rely on more than just the field name. For instance, if your field requires an IP address from the user, you can enter 'management_ip' here and Cacti will fill this field in with the current IP address of the selected host. Valid values for this field are: 'hostname', 'management_ip', 'snmp_community', 'snmp_username', 'snmp_password', and 'snmp_version'.
Update RRD File (Output Only) Check this box if you want Cacti to insert the return value from this field into the RRD 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.

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 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:


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


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.

Note: Spine requires, that multiple parameters are spit out by a single “print” statement. Do not print them in a loop!

Walkthrough: My First Data Input Method

Data Input Method returning a single value

Lets start with a simple script, that takes a hostname or IP address as input parameter, returning a single value. You may find this one as <path_cacti>/scripts/


# take care for tcp:hostname or TCP:ip@
$host = $ARGV[0];
$host =~ s/tcp:/$1/gis;

# old linux version use "icmp_seq"
# newer use "icmp_req" instead
open(PROCESS, "ping -c 1 $host | grep 'icmp_[s|r]eq' | grep time |");
$ping = <PROCESS>;
$ping =~ m/(.*time=)(.*) (ms|usec)/;

if ($2 == "") {
        print "U";              # avoid cacti errors, but do not fake rrdtool stats
}elsif ($3 eq "usec") {
        print $2/1000;  # re-calculate in units of "ms"
        print $2;

To define this script as a Data Input Method to cacti, please go to Data Input Methods and click Add. You should see:

Add a new Data Input Method

Please fill in Name, select Script/Command as Input Type and provide the command that should be used to retrieve the data. You may use <path_cacti> as a symbolical name for the path_to_your_cacti_installation. Those commands will be executed from crontab; so pay attention to providing full path to binaries if required (e.g. /usr/bin/perl instead of perl). Enter all Input Parameters in <> brackets. Click create to see:

Enter Data for new Data Input Method

Now lets define the Input Fields. Click Add as given above to see:

Add new Input Field

The DropDown Field [Input] contains one single value only. This is taken from the Input String <host> above. Fill Friendly Name to serve your needs. The Special Type Code allows you to provide parameters from the current Device to be queried. In this case, the hostname will be taken from the current device. Click create to see:

Data Input Method with first Input Parameter

At least, define the Output Fields. Again, click Add as described above:

Add new Output Field

Provide a short Field [Output] name and a more meaningful Friendly Name. As you will want to save those data, select Update RRD File. Create to see:

Final Data Input Method

Click Save and you're done.

Create the Data Template

Now you want to tell cacti, how to store the data retrieved from this script. Please go to Data Templates and click Add. You should see:

Add new Data Template

Fill in the Data Templates Name with a reasonable text. This name will be used to find this Template among others. Then, please fill in the Data Source Name. This is the name given to the host-specific Data Source. The variable |host_description| is taken from the actual Device. This is to distinguish data sources for different devices. The Data Input Method is a DropDown containing all known scripts and the like. Select the Data Input Method you just created. The Associated RRA's is filled by default. At the moment there's no need to change this. The lower part of the screen looks like:

First Part of Data for new Data Template

The Internal Data Source Name may be defined at your wish. There's no need to use the same name as the Output Field of the Data Input Method, but it may look nicer. Click create to see:

Internal Data Source Name for new Data Template

Notice the new DropDown Output Field. As there is only one Output Field defined by our Data Input Method, you'll see only this. Here's how to connect the Data Source Name (used in the rrd file) to the Output Field of the Script. Click Save and you're done.

Create the Graph Template

Now you want to tell cacti, how to present the data retrieved from this script. Please go to Graph Templates and click Add. You should see:

Add new Graph Template

Fill in Name and Title. The variable |host_description| will again be filled from the Device's definition when generating the Graph. Keep the rest as is and Create. See:

Newly Created Graph Template

Now click Add to select the first item to be shown on the Graphs:

Enter First Graph Item

Select the correct Data Source from the DropDown, fill in a color of your liking and select AREA as a Graph Item Type. You want to fill in a Text Format that will be shown underneath the Graph as a legend. Again, Create:

Define First Graph Item

Notice, that not only an entry was made under Graph Template Items, but under Graph Item Inputs as well. Don't bother with that now. Lets fill some more nice legends, see:

Fill Legend for Graph Template

Notice, that the Data Source is filled in automagically. Select LEGEND as Graph Item Type (it is not really a Graph Item Type in rrdtool-speak, but a nice time-saver), and click Create to see:

Graph Template with Legend

Wow! Three items filled with one action! You may want to define a Vertical Label at the very bottom of the screen and Save.

Apply the Graph Template to a Host

Now go to the Devices and select the one of your choice. See the Associated Graph Templates in the middle of this page:

Devices AssDataQuery

Select your newly created Graph template from the Add Graph Template DropDown. Click Add to see:

Added Graph Template

The Template is added and shown as Not Being Graphed. On the top of the page you'll find the Create Graphs for this Host link. Click this to see:

Creating Graph for new Graph Template

Check the box that belongs to the new template and Create. See the results:

Newly Created Graph for this Host

This will automatically

  • create the needed Graph Description from the Graph Template. As you may notice from the success message, this Graph takes the hosts name in it: router - Test ping (router is the hosts name of this example).
  • create the needed Data Sources Description from the Data Template. Again, you will find the Hosts name replaced for |host_description|
  • create the needed rrd file with definitions from the Data Template. The name of this file is derived from the Host and the Data Template in conjunction with an auto-incrementing number.
  • create an entry to the poller_table to instruct cacti to gather data on each polling cycle

You'll have to wait at least for two polling cycles to find data in the Graph. Find your Graph by going to Graph Management, filtering for your host and selecting the appropriate Graph (there are other methods as well). This may look like:

New Graph after little time of polling

Walkthrough: Script with more Output Parameters

The script will be implemented in perl (as I have no profound knowledge of php). As such, it should execute on most platforms.

#!/usr/bin/perl -w

# --------------------------------------------------
# ARGV[0] = &lt;hostname&gt;     required
# ARGV[1] = &lt;snmp port&gt;    required
# ARGV[2] = &lt;community&gt;    required
# ARGV[3] = &lt;version&gt;      required
# --------------------------------------------------
use Net::SNMP;

# verify input parameters
my $in_hostname         = $ARGV[0] if defined $ARGV[0];
my $in_port             = $ARGV[1] if defined $ARGV[1];
my $in_community        = $ARGV[2] if defined $ARGV[2];
my $in_version          = $ARGV[3] if defined $ARGV[3];

# usage notes
if (
        ( ! defined $in_hostname ) ||
        ( ! defined $in_port ) ||
        ( ! defined $in_community ) ||
        ( ! defined $in_version )
        ) {
        print   "usage:\n\n
                $0 &lt;host&gt; &lt;port&gt; &lt;community&gt; &lt;version&gt;\n\n";

# list all OIDs to be queried
my $udpInDatagrams      = ".";
my $udpOutDatagrams     = ".";

# get information via SNMP
# create session object
my ($session, $error) = Net::SNMP->session(
                        -hostname      => $in_hostname,
                        -port          => $in_port,
                        -version       => $in_version,
                        -community     => $in_community,
                        # please add more parameters if there's a need for them:
                        #   [-localaddr     => $localaddr,]
                        #   [-localport     => $localport,]
                        #   [-nonblocking   => $boolean,]
                        #   [-domain        => $domain,]
                        #   [-timeout       => $seconds,]
                        #   [-retries       => $count,]
                        #   [-maxmsgsize    => $octets,]
                        #   [-translate     => $translate,]
                        #   [-debug         => $bitmask,]
                        #   [-username      => $username,]    # v3
                        #   [-authkey       => $authkey,]     # v3
                        #   [-authpassword  => $authpasswd,]  # v3
                        #   [-authprotocol  => $authproto,]   # v3
                        #   [-privkey       => $privkey,]     # v3
                        #   [-privpassword  => $privpasswd,]  # v3
                        #   [-privprotocol  => $privproto,]   # v3

# on error: exit
if (!defined($session)) {
        printf("ERROR: %s.\n", $error);
        exit 1;

# perform get requests for all wanted OIDs
my $result = $session->get_request(
                         -varbindlist      => [$udpInDatagrams, $udpOutDatagrams]

# on error: exit
if (!defined($result)) {
        printf("ERROR: %s.\n", $session->error);
        exit 1;

# print results
printf("udpInDatagrams:%s udpOutDatagrams:%s", # <<< cacti requires this format!


It should produce following output, when executed from command line:

[prompt]> perl localhost 161 public 1
udpInDatagrams:10121 udpOutDatagrams:11102

Where “public” may be replaced by your community string. Of course, the numbers will vary.

The Data Input Method

To define this script as a Data Input Method to cacti, please go to Data Input Methods and click Add.


You should see:


Enter the name of the new Data Input Method, select Script/Command and type in the command to call the script. Please use the full path to the command interpreter. Instead of entering the specific parameters, type <symbolic variable name> for each parameter the script needs. Save:


Now Add each of the input parameters in the Input Fields section, one after the other. All of them are listed in sequence, starting with <host>:








We've used some of cacti builtin parameters. When applied to a host, those variables will be replaced by the hosts actual settings. Then, this command will be stored in the poller_command table. Now Save your work to see


After having entered all Input Fields, let's now turn to the Output Fields, respectively. Add the first one, udpInDatagrams:


Now udpOutDatagrams:


Be careful to avoid typos. The strings entered here must exactly match those spitted out by the script. Double check Output Fields! Now, results should be like


Finally Save and be proud!


The Data Template

The previous step explained how to call the script that retrieves the data. Now it's time to tell cacti, how to store them in rrd files. You will need a single Data Template only, even if two different output fields will be stored. rrd files are able to store more than one output fields; rrdtool's name for those is data source. So we will create

  1. one single Data Template representing one rrd file
  2. two output fields/data sources

The first step is quite the same as Create the Data Template for a simple Data Input Method. For sure, we provide a different name, Example - UDP Packets. Now, let's enter the first data source. Again, its like above. But we now provide the name of udpInPackets, enter a Maximum value of 100,000 and select the Data Source Type of COUNTER.

Data Template - Two DS, Step1

Then save and find

Data Template - Two DS, Step2

Add the second data source by hitting New and provide data for udpOutPackets. Pay attention to select the correct Output Field defined by the Data Input Method.

Data Template - Two DS, Step3

Please pay attention, as Maximum Value for second and following data sources defaults to 100! In most cases, this value won't fit. To deactivate maximum checking, enter 0, else the desired number. Do not forget to select the correct Data Source Type and the Output Field.

The Graph Template

Again, most of this task was already described at Create the Graph Template of the previous chapter. You will define the Graph Template's global data just as in that example. But now, you will want to add both data sources to the graph. Just copy the steps for data source time twice, one for udpInPackets and for udpOutPackets. Add a Legend for both and you're happy.

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