[mrtg] Timestamp problems - lost data

Steve Shipway s.shipway at auckland.ac.nz
Mon Apr 30 03:58:21 CEST 2007

The problem (as I'm sure you know) is that RRDTool will not allow you to
store data for a time previous to its last update timestamp.  IE, you
cant load this historical data into the archive retroactively.
Similarly, when you'd accidentally set the clock forward and stored some
incorrect data for a time in the future, and then set the clock back
correct again, rrdtool then refused to accept any more data until the
last used time had been reached (again).


The only way I can think of to fix this is a bit long-winded.


1) Get your *old* rrd file.  Use 'rrdtool dump' to dump it to XML

2) Get your *new* rrd file.  Also dump this to XML.

3) Write some code (perl?) that will generate a new XML file by reading
the OLD dump up until the specified time, and then read the new file.
Note that you will need to do this for all 4 RRAs.  Also, keep the *new*
file data for everything else (eg, current ds values).

4) Use rrdtool to load the XML file and generate a new .rrd file from it
using 'rrdtool restore'.

5) Back up your existing .rrd file, and swap in this newly created .rrd


This does work (I've done it here under different circumstances) but you
need to be careful.  Also, you need to script it all to run
automatically so it can finish within 5mins and thus you don't lose any
incoming data while the process runs.  Probably you'll want to test it
out on a minor rrd file first before running it on the whole lot.


You can use a similar method to erase incorrect data, move data in time,
or remove spikes.  


Hope this helps, and hope you know enough scripting to code it...





From: mrtg-bounces at lists.oetiker.ch
[mailto:mrtg-bounces at lists.oetiker.ch] On Behalf Of Charles V. Boehnlein
Sent: Saturday, 28 April 2007 05:51
To: mrtg at lists.oetiker.ch
Subject: [mrtg] Timestamp problems - lost data


The server we use for MRTG recently had its system time changed to an
incorrect time.

After changing the system time back to the correct time we continued to
get a "timestamp" error message and the graphs would not display.


How can we fix this problem?


We had to recreate the RRD databases and lost our old history. We saved
those files but don't see a way to import that data back into the
current RRD databases.


Sorry if this is a repeat request but I could not find a search feature
for the mailing list archives and a search on the MRTG web page did not
return any results for this problem.




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