[rrd-users] Re: rrd graph x-axis shift caused by --step

Alex van den Bogaerdt alex at ergens.op.het.net
Fri Jun 16 13:09:46 MEST 2006

On Fri, Jun 16, 2006 at 12:50:55PM +0200, Stefan Finzel wrote:

> drawing one datapoint per day is shifting my graphs x axis by two hours 
> (correlated to my local time zone CEST?) using --step 86400 by rrdtool 
> create. There is no shift using --step 3600. Something obvious was 
> missed here?

> Data are created using the midnight timestamps of the local zone

Data is input using the local time zone but is immediately
normalized to fit in {n*86400} second time steps.  This comes
down to fit in UTC time.

If you say "--step 86400" you are asking rrdtool to have time slots
running from { (n-1)*86400 } to { n*86400 }.

> Dependent of the setting of --step the x-axis is /not shifted. Using 
> --step 3600 will enlarge my rrd files to keep the same time period, 
> won't it?

You have 24 times the amount of rates in your file so yes, your file
will be bigger.  It will be slightly less than 2400% of the file size
you get with step 86400.

> I am not able/allowed to modify the environement variable TZ as it's 
> setting is already used and required by the script.

You can have a separate TZ for rrdtool, just as I show here for date:

$ date;TZ="" date
Fri Jun 16 13:07:03 CEST 2006
Fri Jun 16 11:07:03 UTC 2006

and also:

$ TZ="" date;date
Fri Jun 16 13:07:03 CEST 2006
Fri Jun 16 11:07:03 UTC 2006

As you can see, this TZ is only for one command 

On unix and alike:

TZ="" rrdtool ...whatever...

on dos and alike you may need to call another script that
sets a new time zone: in stead of calling rrdtool directly,
call rrd_tz.bat and let this script set a new time zone before
it calls the real rrdtool

But what about summertime ?

Alex van den Bogaerdt

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