[rrd-users] graphs with logarithmic Y-axis?

[Ofer Inbar]

I sent this to the Ganglia list, but it might be an RRD Tool issue.

  Ganglia is a system that uses daemons to store metrics about system
  performance in RRD files, and has a web interface that generates
  graphs from those metrics using rrdgraph.  It's written in PHP and
  the code passes command line options and graph definitions from
  variables to rrdgraph, though I don't haven't read all the code so I
  don't know how it works in detail.

I seem to have a problem adding -o or --logarithmic to graphs that
otherwise generate just fine; if I try that option no image is made.

 ..........

I've defined a lot of custom graphs to view our Ganglia data, because
most of the metrics we want to see are custom metrics.  I just add new
blocks to the if-else if... structure in graph.php, with new RRD graph
definitions, and plug those into our custom PHP Ganglia front page,
and it works quite well.

There's one set of custom metrics we'd like to view with a logarithmic
Y-axis.  rrdgraph's documentation says it can generate a graph with a
logarithmic Y-axis if you pass it the -o or --logarithmic option.  I
tried adding this to the $upper_limit or $extras variable in the block
defining the graph in question, but when I do that no graph gets
generated at all.

Has anyone succesfully modified graph.php to add graphs with
logarithmic Y-axis?  How'd you do it?

We're running:
  rrdtool 1.2.18
  Ganglia 3.0.1
  RedHat EL 4

  -- Cos