Setting up New Devices in Cricket
Cricket is designed to be flexible enough to be able to monitor
more than just router interfaces. The sample config tree that comes
with it will help you learn about its capabilities, but to monitor
other things, you'll need to write your own branches of the config
Read this document to learn how to get the most from Cricket, by
teaching it to gather data from all kinds of sources.
Creating Custom Target Types
Cricket gives you complete control over the contents and layout of
your RRD files. This means that if you are going to be doing any
serious target-type hacking, you need to understand the following
Now, with all those terms under your belt, you'll understand this
statement: Using the datasource, RRA, and targetType
dictionaries, you can completely control the kind, source, and
quantity of data you store. The RRA's in the sample-config reproduce
2.x's data format precisely, and that configuration has proven to
work well for most needs. If you are going to be using Cricket for the
jobs it comes ready to do, you'll simply need to copy the
sample-config tree and make minor changes to the targets it specifies.
Round Robin Array (RRA)
This is where data is stored in an RRD. There is one RRA for each
scale of data, for example 5 minute samples, 30 minute samples, and 2
hour samples. The same data is in each RRA, except it is sampled at a
different rate. If an RRA can hold 12 samples and it is updated every
5 minutes, then it holds data spanning back one hour. The 13th sample
will overwrite the 1st sample. Detailed information about RRD is
RRD Tool documentation and from the
A data source is one line on a graph, or
one column of data if you think of the RRD as a tabular
listing of data. One RRD can have many datasources in
it. All up them must be updated with new data at once. Not
all of them need to be graphed at once (see the information
about datasource "views" below).
A device that we are keeping stats on is a target. There
one RRD file on disk for every target. You can think of
each target as a leaf on the config tree.
The type of the target determines what kinds of data
sources and RRA's makes up the target. When Cricket goes to
update a target, it uses the target type to figure out what
data to fetch about the target, and how to fetch it.
Data Source Source (ds-source)
This is the rather unfortunate name for the attribute of a data source
that tells Cricket precisely where to fetch the data from, and which
data to fetch. Encoded in the ds-source is the retrieval method and a
description of the data we want.
If you need to customize Cricket to talk to other things, then you'll be
following the following general steps:
Create entries in the datasource dictionary that tell
Cricket how to fetch your new measurement. If you are using
SNMP, you'll probably want to add an entry to the OID
dictionary in the same subtree, to make your datasource entry
readable. For instance, say we wanted to use Cricket to talk via
SNMP to an agent running on a Unix machine, and fetch the load
average. We would add the OID for the load average to the OID
table, then add a new entry (named "load-average") to the
datasource dictionary that described this new datasource.
Create a targetType entry to tell Cricket what
datasources make up your new target-type. Assuming the RRA
definitions from the --default-- entry are right, you only
need to add set the "ds" tag for this entry. For the load average
example, we'd put "ds=load-average" into a targetType entry
Create a new target who's target-type tag is set to
the targetType you created in the last step. If you are using
SNMP to talk to the host, you need to make certain the
variable snmp-host is set (since it contributes to the snmp
variable, which in turn is required in SNMP ds-sources). You
could set the snmp-host tag explicitly for every tag, but that
would be a pain. Instead, you could choose your target names
to be hostnames, then use the auto-target-name to set
snmp-host correctly all the time, by adding a line like
snmp-host = %auto-target-name% to the --default-- entry for
that sub-tree. If you have a rare case in your system where
the target name is not the name you want to send SNMP packets
to, then you could override the default snmp-host by setting
snmp-host directly for that one target.
Run the collector on your new subtree, using the
"-loglevel debug" option. This will tell you exactly what
Cricket thinks things are set to when it tries to fetch your
data, as well as what exactly happened when it went to fetch
If you come up with an interesting configuration, please share it
with the Cricket community by subitting it to the
contrib site hosted by the nice folks at
If you need to add a new kind of data gathering subroutine, you'll
want to read the code to snmp.pm very carefully and make a
module like it to collect your data. It's not too hard, but it might
not be worth the effort -- consider using a simple Perl script to let
you fetch the data via the exec method. See the
http-performance sub-tree for an example of how to do this.
version 1.0.2, released 2000-05-19.
Copyright (C) 1998-2000 Jeff Allen. Cricket is released under
the GNU General Public License.