[mrtg] Strange error when using UCD-DISKIO-MIB

Freddie Cash fjwcash at gmail.com
Thu Feb 19 17:28:14 CET 2009

On February 18, 2009 2:47 pm Freddie Cash wrote:
> I'm trying to monitor the disk I/O for a couple of servers, using MRTG.
> However, no matter what I try, it will not update the RRD file, and gives
> strange "unknown SNMP var" errors.
> However, using the exact same config file, but with snpo debugging
> enabled, the SNMP get works, but again without updating the RRD file.
> The config file I use for testing is below.

Further testing shows that if I set "Forks: 1" then I can run mrtg in debug 
mode (snpo) and the checks and RRD updates occur correctly.  If I set 
"Forks: 10" or higher, it fails (unknown SNMP var) ... even in debug mode.

Also, if I try to check all 48 drives in both servers via a single config 
file/mrtg run, then it fails.  If I split the config file to check the two 
servers one after the other in separate mrtg runs (24 drives each), then it 

Not sure what else to check.  For now, I've copied /usr/bin/mrtg to 
/usr/bin/mrtg.debug, enabled snpo debugging, and running that via cron to 
get disk I/O monitoring.  Not ideal in any way (especially since I can't 
query the 64-bit counters) ... but it mostly works for now.

fjwcash at gmail.com

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