Nicolas' Blog

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.

The next ubuntu release, 10.04 is planned to be released on April 29th 2010. While the date is closing by rapidly, the development process is right on its track.

With a first beta release mid-March which allowed to spot some nasty bugs of all kind, the community is now working towards a second beta. Beta 2 is already past “freeze”, the point at which any additional change to the core packages of the distribution is subject to a process known as “freeze exception” for which good motivations must exist and thorough review is performed  by the release managers to make sure nothing that works is affected by the proposed change.

Needless to say, Lucid Lynx beta 2 will be a much more stable version with many bugfixes when its released on April 8th.

Areas in which you can still help at this points are:

• installing beta 2 and reporting bugs which are not yet reported or adding information to the existing report that might help track it down
• participating in the translation process through the translators groups until April 22nd.

The next step is to get a release candidate version on the 22nd for a final release of Lucid Lynx 10.04 LTS on April 29th! Get involved!