Cacti’s Realtime plugin graphs fine no RRAs written

cactirrdtool

Got a Cacti instance (CactiEZ with cacti 088a) where I successfully graph with number of bespoke data template and corresponding graph template.
Theres one specific however case where the RRAs are simply not written out. The OID is correct. with Realtime It graphs correctly but when looking at the graph anywhere else on Cacti (tree/graph management/editing a host/debug mode on the graph) RRDTool "says" ERROR: opening [..] No such file or directory

/usr/bin/rrdtool graph - \
--imgformat=PNG \
--start=-86400 \
--end=-60 \
--title='HOSTDESCRIPT - Volts' \
--base=1000 \
--height=120 \
--width=500 \
--alt-autoscale-max \
--lower-limit='0' \
--vertical-label='Volts' \
--slope-mode \
--font TITLE:10: \
--font AXIS:8: \
--font LEGEND:8: \
--font UNIT:8: \
DEF:a="/var/www/html/rra/correctfilename.rrd":'lib_100_v':LAST \
--watermark "bla" \
LINE1:a#4444FFFF:""  \
GPRINT:a:LAST:"Last\:%8.2lf%s"  \
GPRINT:a:AVERAGE:"Average\:%8.2lf%s"  \
GPRINT:a:MIN:"Min\:%8.2lf%s"  \
GPRINT:a:MAX:"Max\:%8.2lf%s\n"

So:
Why fail on only one template (which works btw on an older 087c cacti but I've checked and eyeballed the template for 3 days!).
Why would Realtime plugin graph it perfectly?

More importantly – whats the difference between the way normal graphing and polling use of templates and how Realtime uses templates? As I think the difference would point to the cause of the issue.

Best Answer

Realtime doesn't use the standard Cacti rra files. It effectively has it's own poller, and it's own temporary RRDtool files with finer detail settings, to support the faster polling. You can see those files in the realtime-cache folder which you would have set up when installing Realtime.

I'd see what happens if you use that command from a shell (replace that first '-' with 'temp.png' or you will get raw PNG data sent to stdout). If rrdtool does produce a PNG then you know that side is OK.

Also check the cacti.log for the DS ID number (the number in the end of the rrd filename) - usually you'll get some information in there if it's trying to write the file.

The Cacti manual's debugging page is actually pretty good for following through what is going on - there are a lot of moving parts, and it's not all obvious!

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