MRTG lang=C why and howto

In my previous post on MRTG, I showed how to plot various sensor and network traffic readings so that they can be easily visualized. In modern systems one can however run into another problem: in UTF-8 enviroments, MRTG starts to complain: 

~#:echo $LANG 

en_us.UTF-8 

~#:mrtg 

ERROR: Mrtg will most likely not work propperly when the environment
variable LANG is set to UTF-8. Please run mrtg in an environment
where this is not the case:

env LANG=C /usr/bin/mrtg

So we shall use the command line given above. However, simply setting LANG=C turns out not be enough, and we get further error messages with previously working mrtg.cfg file such as follows: 

~#:env LANG=C /bin/mrtg /etc/mrtg/mrtg.cfg --logging /var/log/mrtg.log 

...

2010-11-26 16:05:22 -- SNMPGET Problem for hrSystemUptime.0 sysName on public@localhost
 at /bin/mrtg line 658
2010-11-26 16:05:22 -- 2010-11-26 16:05:12: ERROR: Target[localhost.cpu0][_IN_] ' $target->[1]{$mode} ' did not eval into defined data
2010-11-26 16:05:22 -- 2010-11-26 16:05:12: ERROR: Target[localhost.cpu0][_OUT_] ' $target->[1]{$mode} ' did not eval into defined data
2010-11-26 16:05:32 -- SNMP Error: 

no response received

The problem turns out to be that the textual SNMP targets do not work anymore, and the numeric OIDs such as .1.3.6.1.2.1.25.3.3.1.2.768 have to be put in mrtg.cfg. Not only this is inconvenient, the proper numeric values have to be found as well. In order to do so, the snmptranslate tool can be used:

~#: snmptranslate HOST-RESOURCES-MIB::hrProcessorLoad.768 -On

.1.3.6.1.2.1.25.3.3.1.2.768

Here the main point is the -On switch, which translates the name of the OID to the corresponding numerical value. All textual targets in mrtg.cfg must be replaced using the output of this tool. This includes the previously discussed lm-sensors outputs as well. Here is an example for CPU usage:

# commented old one

#Target[localhost.cpu0]: hrProcessorLoad.768&hrProcessorLoad.768:public@localhost
#new one follows

Target[localhost.cpu0]:.1.3.6.1.2.1.25.3.3.1.2.768&.1.3.6.1.2.1.25.3.3.1.2.768:public@localhost 

and then MRTG works again!

Lm-sensors in net-snmp

Readout of integrated motherboard sensors was already a topic here, for VIA Epia boards and for WD Mybook World Edition as well. Such data is good to have visualized, so plotting it using MRTG was discussed too. This tool and its fundamental, net-snmp was designed to visualize network traffic data, so for sensor readings, an external script had to be constructed, which was quite inconvenient.

There is however a better way, briefly mentioned by lm-sensors.org, for which net-snmp has to be installed from source (download here, install instructions here) and has to be configured with the following options:

~$: cd net-snmp

~$: ./configure --with-mib-modules="ucd-snmp/lmsensorsMib" --with-ldflags="-lsensors" 

~$: make

~$: sudo make install

If installation was successful, lm-sensor readouts can be accessed via snmp, the same way as if they were polled by the command-line sensors tool:

~#: sensors

coretemp-isa-0000
Adapter: ISA adapter
Core 0:      +33.0 °C  (high = +78.0 °C, crit = +100.0 °C) 

coretemp-isa-0001
Adapter: ISA adapter
Core 1:      +32.0 °C  (high = +78.0 °C, crit = +100.0 °C) 

~#: snmpwalk -v 2c -c public localhost Sensors

LM-SENSORS-MIB::lmTempSensorsIndex.1 = INTEGER: 1
LM-SENSORS-MIB::lmTempSensorsIndex.2 = INTEGER: 2
LM-SENSORS-MIB::lmTempSensorsDevice.1 = STRING: Core 0
LM-SENSORS-MIB::lmTempSensorsDevice.2 = STRING: Core 1
LM-SENSORS-MIB::lmTempSensorsValue.1 = Gauge32: 33000
LM-SENSORS-MIB::lmTempSensorsValue.2 = Gauge32: 32000

Sadly, only CPU core temperatures can be read out for ICH8/ICH9 chipsets at the moment, still it is now way easier to integrate lm-sensor readings to net-snmp based logging and plotting tools such as MRTG.