RRDGRAPH_DATA(1) rrdtool RRDGRAPH_DATA(1)
rrdgraph_data - preparing data for graphing in rrdtool graph
These three instructions extract data values out of the RRD files,
optionally altering them (think, for example, of a bytes to bits con
version). If so desired, you can also define variables containing use
ful information such as maximum, minimum etcetera. Two of the instruc
tions use a language called RPN which is described in its own manual
Variable names (vname) must be made up strings of the following charac
ters "A-Z, a-z, 0-9, -,_" and a maximum length of 255 characters.
When picking variable names, make sure you do not choose a name that is
already taken by an RPN operator. A save bet it to use lowercase or
mixedcase names for variables since operators will always be in upper
This command fetches data from an RRD file. The virtual name vname can
then be used throughout the rest of the script. By default, an RRA
which contains the correct consolidated data at an appropriate resolu
tion will be chosen. The resolution can be overridden with the --step
option. The resolution can again be overridden by specifying the step
size. The time span of this data is the same as for the graph by
default, you can override this by specifying start and end. Remember
to escape colons in the time specification!
If the resolution of the data is higher than the resolution of the
graph, the data will be further consolidated. This may result in a
graph that spans slightly more time than requested. Ideally each point
in the graph should correspond with one CDP from an RRA. For instance,
if your RRD has an RRA with a resolution of 1800 seconds per CDP, you
should create an image with width 400 and time span 400*1800 seconds
(use appropriate start and end times, such as "--start
If consolidation needs to be done, the CF of the RRA specified in the
DEF itself will be used to reduce the data density. This behaviour can
be changed using ":reduce=". This optional parameter specifies the
CF to use during the data reduction phase.
This command returns a value and/or a time according to the RPN state
ments used. The resulting vname will, depending on the functions used,
have a value and a time component. When you use this vname in another
RPN expression, you are effectively inserting its value just as if you
had put a number at that place. The variable can also be used in the
various graph and print elements.
Note that currently only agregation functions work in VDEF rpn expres
sions. Patches to change this are welcome.
This command creates a new set of data points (in memory only, not in
the RRD file) out of one or more other data series. The RPN instruc
tions are used to evaluate a mathematical function on each data point.
The resulting vname can then be used further on in the script, just as
if it were generated by a DEF instruction.
rrdgraph gives an overview of how rrdtool graph works. rrdgraph_data
describes DEF,CDEF and VDEF in detail. rrdgraph_rpn describes the RPN
language used in the ?DEF statements. rrdgraph_graph page describes
all of the graph and print functions.
Make sure to read rrdgraph_examples for tips&tricks.
Program by Tobias Oetiker
This manual page by Alex van den Bogaerdt
1.2.15 2006-07-14 RRDGRAPH_DATA(1)
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This page was generated Thu Apr 30 17:05:22 2009