[mrtg] Explicit OID not populating logs correctly

[Joshua Wright]

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I'm trying to log data from an explicit OID to track the number of
packets that fail transmission on a wireless access point.

Using Net-SNMP, I'm able to extract information from this counter type
and I see the value increment:

$ snmpget -c public 172.16.0.92 .1.2.840.10036.2.2.1.3.1
iso.2.840.10036.2.2.1.3.1 = Counter32: 83484
$ sleep 120
$ snmpget -c public 172.16.0.92 .1.2.840.10036.2.2.1.3.1
iso.2.840.10036.2.2.1.3.1 = Counter32: 83488

I put together a simple mrtg.cfg to collect information about this MIB
entry:

$ cat mrtg.cfg
WorkDir: /home/jwright/failedtx
Target[172.16.0.92_1]:
.1.2.840.10036.2.2.1.3.1&PseudoZero:public at 172.16.0.92
Title[172.16.0.92_1]: dot11FailedCount - excessive retries that failed to TX
MaxBytes[172.16.0.92_1]: 4096000

And I am able to reference this file and collect the MIB data:

$ /usr/local/mrtg-2/bin/mrtg mrtg.cfg
Rateup WARNING: /usr/local/mrtg-2/bin/rateup could not read the primary
log file for 172.16.0.92_1
Rateup WARNING: /usr/local/mrtg-2/bin/rateup The backup log file for
172.16.0.92_1 was invalid as well
Rateup WARNING: /usr/local/mrtg-2/bin/rateup Can't remove
172.16.0.92_1.old updating log file
Rateup WARNING: /usr/local/mrtg-2/bin/rateup Can't rename
172.16.0.92_1.log to 172.16.0.92_1.old updating log file
$ /usr/local/mrtg-2/bin/mrtg mrtg.cfg
Rateup WARNING: /usr/local/mrtg-2/bin/rateup Can't remove
172.16.0.92_1.old updating log file
$ /usr/local/mrtg-2/bin/mrtg mrtg.cfg
$


My problem is that the log file doesn't appear to be collecting the
information properly.  Each time I run "mrtg", the .log file is updated,
but no previous statistics are collected.  For example:

$ head 172.16.0.92_1.log
1126832868 83493 0
1126832868 0 0 0 0
1126832866 0 0 0 0
1126832700 0 0 0 0
1126832400 0 0 0 0
1126832100 0 0 0 0
1126831800 0 0 0 0
1126831500 0 0 0 0
1126831200 0 0 0 0
1126830900 0 0 0 0
$ sleep 300 ; /usr/local/mrtg-2/bin/mrtg mrtg.cfg
$ /usr/local/mrtg-2/bin/mrtg mrtg.cfg
$ head 172.16.0.92_1.log
1126833288 83505 0
1126833288 0 0 0 0
1126833277 0 0 0 0
1126833000 0 0 0 0
1126832700 0 0 0 0
1126832400 0 0 0 0
1126832100 0 0 0 0
1126831800 0 0 0 0
1126831500 0 0 0 0
1126831200 0 0 0 0
$

For some reason, mrtg is replacing the previous logging entry instead of
retaining the historical statistics.  Did I not configure my mrtg.cfg
file appropriately to collect information from this MIB entry?

Thanks!

- -Josh
- --
- -Joshua Wright
jwright at hasborg.com

2005-2006 pgpkey: http://802.11ninja.net/pgpkey.htm
fingerprint: F00E 7A42 8375 0C55 964F E5A4 4D2F 22F6 3658 A4BF

Today I stumbled across the world's largest hotspot.  The SSID is "linksys".
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