Changing the timezone of cacti graphs using rrdtool
I’ve recently come accross an interesting problem while trying to use a cacti install running on a server located in Europe in order to monitor, generate and export statistics to be read by people in Central America. Indeed, the generated graphs indicated CET time while the people for whom the graphs were interested expected UTC-6 time.
While there has been a support request in cacti for this particular feature and I’ve come across a patch for 0.8.6 on cacti forums, I haven’t found a solution that is integrated into cacti. So I went for an external graph generation script.
Cacti generates graphs by invoking rrdtool which itself relies on the value of the TZ environment variable to determine the offset that it must apply to variables stored inside the database. Indeed, the time stored in an rrd is UTC by default and an offset is applied during graph generation in order to transpose this to any local time according to the value of the TZ variable.
The script I’ve created simply uses the command line I got from cacti by turning graph debugging on in the graph management for the particular graph I wanted to export.
TZ="America/El_Salvador" /usr/bin/rrdtool graph - --imgformat=PNG --start=-86400 --end=-300 --title="My graph title" --base=1000 --height=120 --width=500 --alt-autoscale-max --lower-limit=0 --vertical-label="" --slope-mode --font TITLE:12: --font AXIS:8: --font LEGEND:10: --font UNIT:8: DEF:a="/var/lib/cacti/rra/my_file.rrd":somefield:AVERAGE AREA:a#AFECEDFF:"" > somefield_1.png
The TZ=”America/El_Salvador” part of the command line redefines the value of the TZ environment variable before executing rrdtool. This modification is only local to the process from which rrdtool is launched and does not affect the current shell. The TZ variable is part of the zoneinfo package, the full list of possible values for this variable can be found under the /usr/share/zoneinfo directory of any linux machine.
--start=-604800 --end=-1800 --start=-2678400 --end=-7200 --start=-33053184 --end=-86400
MAILTO=myusername */5 * * * * www-data /path/to/myscript.sh >/dev/null 2>&1
Using this trick, I can now generate graphs that make sense to the people they’re intended for without asking them to perform the conversion from UTC by themselves.
Tags: cacti, rrdtool, Ubuntu
Line two of graph_image.php — add this:
putenv(‘TZ=America/Los_Angeles’);
or whatever timezone you want, and tada! Works. Older cacti versions didn’t have this issue. Supported timezones:
http://www.php.net/manual/en/timezones.php
Much simpler approach. I only wanted to shift timezone on some of the graphs I export, thus the more complex approach. Thanks for this great tip!
This article is what I was looking for, I had the same issue since from Cacti server need to generate graphs in many diferent TZ (many countries). I am able to generate the png file (a graph with custom tz) as you mention in script (> somefield_1.png.) However I am not sure how can I integrate/update this file with the actual cacti tree in the user GUI??.