RRDTool - Not a valid vname - bash

Question

I am using RRDTool to manage and graph my Performance Data.
Currently, I am calling RRDTool from a bash script, but I get an Error, which I can not fix.
My Bash Script looks like this:
# Call RRDTool and save the output
output=$(rrdtool graph --width 4000 \
DEF:data=/usr/local/pnp4nagios/var/perfdata/FM/win_tcpu.rrd:proc:AVERAGE \
VDEF:slope=data,LSLSLOPE \
PRINT:slope:'%lf')
echo "Output: " $output
I am trying to solve for m in y = m*x + b with this simple example.
My Performance Data looks something like this:
<NAGIOS>
<DATASOURCE>
<TEMPLATE>nrpe_win_tcpu</TEMPLATE>
<RRDFILE>/usr/local/pnp4nagios/var/perfdata/FM/win_tcpu.rrd</RRDFILE>
<RRD_STORAGE_TYPE>SINGLE</RRD_STORAGE_TYPE>
<RRD_HEARTBEAT>8460</RRD_HEARTBEAT>
<IS_MULTI>0</IS_MULTI>
<DS>1</DS>
<NAME>proc</NAME>
...
</DATASOURCE>
...
As you can see the file name is correct and the DataSource Name is also correct.
My Problem is that the DEF does not seem to work. I get the following Error Message:
ERROR: Not a valid vname: data in line VDEF:slope=data,LSLSLOPE
When trying to access the data saved in Variable data like this, just to check if the problem is in my VDEF line:
LINE1:data#0000FF:"data" \
I get the following Error:
ERROR: parameter 'data' does not represent a number in line LINE1:data#0000FF:data
This clarifies that the problem is somewhere in the DEF line but I have no clue why this is happening.
Does anybody have an idea why I get these error messages and how to fix this problem?
Any help appreciated. Thanks in advance.

Answer 1

I found the problem. It was only a really dumb mistake I made.
I was calling:
rrdtool graph --width 4000 \
DEF:data=/usr/local/pnp4nagios/var/perfdata/FM/win_tcpu.rrd:proc:AVERAGE \
VDEF:slope=data,LSLSLOPE \
...
Looking in the usage description of RRDTool graph again, showed me this:
rrdtool graph filename [-s|--start seconds] [-e|--end seconds] ...
I was simply missing a filename. When calling it like mentioned above RRDTool interpreted my DEF line as a filename. This would cause an error when writing the result to this file, but RRDTool exits with an error on the VDEF line, since data was never defined.
Thanks for all the comments. I just wanted to clarify some things I tested:
- The variable Name data does not cause any problems
- It is totally working to have a DS with name 1 and you could also access it in a CDEF and so on
Thanks for the help!

Answer 2

You can't do a line of a VDEF - it's a value, and is only valid with an aggregation function.
From: http://oss.oetiker.ch/rrdtool/doc/rrdgraph_rpn.en.html LSLSLOPE is valid.
You should be able to graph data though, e.g.
LINE1:data#00CC00:data
That you can't - and get 'does not represent a number' makes me wonder what's in you data source. I would suggest you have a look at xport to dump the RRD and see what's in there.
You might well be not getting enough input data to build a CDP within your RRD, and so they're all UNKNOWN or NaN.
(Invalid VNAME does make me wonder though - have you tried changing it to something other than data - which seems like it could be a reserved word.)