[rrd-users] --alt-autoscale question

Steve Shipway s.shipway at auckland.ac.nz
Mon May 12 00:04:37 CEST 2014

> /usr/bin/rrdtool grap - --width=500 --height=100 --start 139979062
> label "" --title "lab_e102 / Check lab temperature" --alt-autoscale
> However, the lower limit on the y-axis will never be adjusted and always
> remain zero in the plot.

The graph you attach appears to show a Y-axis lower limit of less than zero
(see the gap at the bottom).  Maybe something like -1.   The autoscale is
clearly starting around the data value, but something is expanding it down
to -1 or thereabouts.  Unless you can supply us with the complete RRDTool
graph command line for comparison it makes it very difficult to identify the
reason -- possibly you have an additional line on the graph or something
we're not aware of.

> /usr/bin/rrdtool grap - --width=500 --height=100 --start 139979062
> label "" --title "lab_e102 / Check lab temperature" -l 21.0 -r
> will give me a scale that starts at 21.0 Celsius as expected. What am I
> here? I am attaching a picture of the graph generated with
> but I am not sure it will make it to the list. The plot has values for min
> max included, and they are correct, so --alt-autoscale should work.

In this example, you force a lower limit of 21 and use -r (rigid) to lock it
from expanding, so you get what you asked for (though it is hardcoded and
not automatically adjusted).  The upper limit will still expand to whatever
your data maximum is.

If you omit the -r, do you get a graph like you want, or does it go back to
zero or less?  If the former, it might indicate a problem in the
alt-autoscale code, but I would expect you'd get the latter indicating that
it is the autoexpansion of the Y-range caused by some additional graph lines
or data that you have not  shown.


Steve Shipway
s.shipway at auckland.ac.nz

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