[mrtg] Problem with nulls in RRD files

Steve Shipway s.shipway at auckland.ac.nz
Tue Jun 17 00:27:14 CEST 2008

If you can see the date and time on the .rrd files changing regularly, then this confirms that MRTG is running, and updating the RRD files.  Therefore, the problem is that nulls are being stored.

If nulls are being stored, there are a few possible causes:

1) The data really is null.  Maybe the device being monitored is down or unreachable, or your community string is wrong.  Check the output of MRTG when run interactively to look for error messages.
2) The data is out of bounds.  If you have MaxBytes or AbsMax set to a too-low value, then retrieved data may be seen as too large and so a null is stored.
3) When you do an rrdtool dump, look at the beginning for the PDP Status.  See what 'value' and 'unknown_sec' are, these show the last values retrieved.

BTW - try starting a new thread in the mailing list for a new question.  Also, there are MRTG/RRD/Routers2 support forums (fora?) available on http://www.steveshipway.org/forum


From: Mersberger, Robert [mailto:robert.mersberger at goldenliving.com]
Sent: Tuesday, 17 June 2008 10:13
To: Steve Shipway; Eric Hernandez; mrtg at lists.oetiker.ch
Subject: RE: [mrtg] graphing more than two values with mrtg/rrdtool

maybe this is not the place to ask this but, I need help.

I have just installed mrtg, rrdtool and rouers2.cgi on a fedora fc9  and seem to have all things functioning correctly except for updating the rrd_data files for the site I am polling.
If I do an ls -al of the rrd_data directory I can watch the date and time change with each run of my mrtg script.  if I dump one of the rrds I only seen nulls,

Can anyone help me this this?

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