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!