[rrd-users] only getting nan values

Simon Hobson linux at thehobsons.co.uk
Thu May 26 12:20:39 CEST 2016

Jim Sher <rrdtool at blyzz.com> wrote:

> I'm using cron to run a script every 5 minutes to get some values and update the RRD files and then draw the graphs.
> My script to populate the RRAs in the RRD:
> But when I view the graphs (all of them are like the one below), all the values are not numbers (nan).

Two common problems :

1) How long did you let your collection script run for ? One update is *NOT* sufficient to create any known values in the database.

2) Post the commands used to create the RRD files. A common mistake is to make heartbeat only 300s and update "every 5 minutes". "Every 5 minutes" often isn't "every 300s", especially when using "N" as the timestamp. If two updates are 301s apart, a heartbeat of 300s means "unknown" data will be stored.

Try "rrdtool fetch" to see what's stored in the database - it's easier than trying to work out if it's the data or the graphing that's causing the problem.

For reference, see http://rrdtool.vandenbogaerdt.nl
In particular, "Rates, normalizing and consolidating" should make things a lot clearer.

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