mod_rrd_graph with raspberrypi

[mbretschn]

Hello,

i configured my nginx with mod_rrd_graph. It partially works, because i got a typical rrdgraph png.
Unfortunately without data, same command works when started on cmd. No errors found in error.log.

Where should i look for fixing this?

RRDtool 1.4.8, nginx/1.13.12, Raspbian GNU/Linux 8 (jessie)