[rrd-users] Adding an element to a graph

Alex van den Bogaerdt alex at ergens.op.het.net
Thu Mar 1 18:20:49 CET 2007

On Thu, Mar 01, 2007 at 11:12:17AM -0500, Cole Tuininga wrote:

> I'm dynamically building an rrdgraph call after my program hunts
> around for several rrd files to aggregate from.  The problem is that
> the requested data won't always have any rrd files, but I still want
> to have it available as an item in the graph.
> My thought was to create a placeholder CDEF - something like
> CDEF:placeholder=0
> or, if necessary
> CDEF:placeholder=0,0,+
> So that I can do a:
> LINE:placeholder#0000FF:Blah
> However, these don't seem to work.  It's not enough to simply add in
> an "extra" item to the legend without graphing the data - this may be
> the only item.  In that scenario, no graph would be generated, so
> there would be no legend to add to.  :)

Provided that your CDEF works, why would a graph not be created if you
use LINE ?

If you have a graphing element (LINE, AREA) then a graph is created. If
that's not happening and if you don't see error messages, you are throwing
thse error messages away.

Alex van den Bogaerdt

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