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For some reason Collectd works fine on all my virtual servers, but on the dom0 of my Xen setup it keeps returning a value of NaN, I have checked the RRD files and it seems somehow all plugins are returning NaN values.

Now NaN meaning "Not a Number" I wonder why it's not getting numbers from its plugins. Any idea what this might be, I can only think it's Xen related as it only happens on the host, and not on the VMs


Worth noting, I have tested making collectd write to local rrd files, so not sending to a central server, and those RRD files also all contained NaN values.

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Have you ran snmpwalk on the host/OIDs to verify that whatever you're trying to get info from exists at that OID? – Kendall Jun 2 '11 at 22:34
What plugins are you using? Are you sending the data from collectd on dom0 to the same collectd server that the VMs are sending the data to? – sciurus Jun 2 '11 at 23:12
@sciurus Yes it's sending the data to the same host as all the VMs. and plugins, it just uses some of the default ones cpu, disk, interface, load, etc – Not Available Jun 3 '11 at 1:16
NaN is the result of a division by zero. Not sure that helps, but FYI :) – Halfgaar Jun 3 '11 at 10:30
@Halfgaar: That is true, but not the only cause of NaN. For example, if the plugin is requesting an OID that does not exist on that host, you'll get something along the lines of "No such service(?) exists at this OID". I don't remember the specific message. But, that will also give you a NaN value. – Kendall Jun 3 '11 at 17:01

Check the time on the dom0 host.

Chances are the clocks on your collectd collector and the dom0 system are out of sync.

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It also happens when not using a remote server but local RRD files, I have updated my question with this info, should've noted it. – Not Available Jun 11 '11 at 10:29
up vote 0 down vote accepted

Okay so the issue has apparently disappeared, the statistics are now being reported correctly, now I have recently done 2 things (If I recall correctly):

  • Updated the kernel to a newer version
  • Updated collectd

I think it might've been a kernel bug that was the culprit, anyway, it's working again now, thank you all for your time.

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