[rrd-users] rrdtool without accurate time

Joel Lindsay joel at waveteq.com
Thu Nov 30 23:30:40 MET 2006

I have no clock on my embedded system so am having problem using rrdtool 
correctly.  I can add a fake date and therefore enter info into the RRD but 
2 problems exist.

1) A reboot changes the date back to the start and then can't add to the rrd 
database until time elapses past the last uptime
2)  I can't get x-axis to use relative numbers instead of absolute.

I could recreate the database everytime I boot and this could work OK but 
only keep records from last reboot.  Or I could try setting the date based 
on the last entry in the rrd + 1 minute and then continue adding new values 
after reboot (assume always up so no downtime)  This wouldn't be perfect but 
would work.

For the graph though, I would like my x-axis to show the last hour, day or 
week but with relative times instead of absolute time, since the absolute 
times stored in the database are not right anyway.  At present, my labels 
show the absolute time, and shift the gridlines to correspond.

For example - Right now if I do a last hour (with labels at 15 minutes) 
graph I see the gridlines shift and labels show up as 00 15 30 45, shifted 
to correspond to the fake time in the database.  Instead, I would like to 
have labels that say -60 -45 -30 -15 0, where -60 is always at the x axis 
intersecting with the y axis and 0 is always at the far right of graph (no 

Is this possible?  Can anyone give me some tips to do this right?  Can I use 
relative time for my graph labels?

I am using rrd-tool 1.0.45 because I couldn't get newer versions to cross 
compile with the arm ixp-4xx processor due to ieee floating point configure 


Joel Lindsay, B.Eng
Project Engineer
Waveteq Communications
(250) 766-9229
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