[rrd-users] Help in constructing 2 second update graph

Simon Hobson linux at thehobsons.co.uk
Sat Dec 22 11:40:38 CET 2012

EHCanadian wrote:

>$RRDToolPath & ' create ' & $RRDDataPath & 'WiFiSignal.rrd --step 2
>DS:WiFiSignal:GAUGE:4:0:100 RRA:LAST:0.5:2:120

There's an error there to start with. You are consolidating two off, 2 second samples into each consolidated data point. Thus you are storing 8 minutes at 4 second resolution.

In the general case, you wouldn't normally want to use LAST as your consolidation function. Normally you would want to consolidate for MIN, MAX, and AVERAGE. However, in your case, since your consolidation should be a null function, you can get away with it.

>$RRDToolPath & ' graph ' & $RRDDataPath & 'WiFiSignal.png -E -G mono -R mono
>-a PNG -w 800 -h 600 --full-size-mode --start end-1minute --title="WiFi
>Signal 1 Min" --vertical-label="WiFi Signal Strength" DEF:WiFiSignalDef=' &
>StringReplace($RRDDataPath,'C:','C\:') & 'WiFiSignal.rrd:WiFiSignal:LAST

You haven't specified an end time, so you'll get an arbitrary graph ending at whatever "now" is when you run the command. That may or may not be what you want.

OK, so if this doesn't help, here is what you need to do.
1) Make a file with test data. Your inputs are variable and time-dependent, so nothing can be reproduced.
2) Make direct calls to RRDTool - ie leave out the programming environment specific stuff to start with.

So now you should have known data, and fixed commands. You can run the commands and see what happens. Because the data is fixed, you should know what to expect, and others can too.

If you are still stuck, post the data and commands here.

Once you have that working, you can "scriptify it" - if it then stops working, you have a knwon working point you can go back to.

Also, you may find Alex's tutorials helpful :

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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