Thanks guys for all the suggestions. None of it changed the situation but I'm beginning to think that it might have to do with SNMP not accepting word names in MRTG, or more specifically some kind of language encoding issue. This is because of the following reasons 1. It's been pointed that out that MRTG need to be started with the options env LANG=C because it won't work properly if LANG is UTF8 2. On some options I try in MRTG, the log shows some error about Wide characters returned from SNMP, and I see a chinese character, which obviously shouldn't be a return value. 3. Addressing SNMP variables by name does not work in MRTG, but works from command line. e.g. something like ssRawCpuLoad is fine in command line, but does not work in MRTG config file, only the dot-numeric equivalent would return some kind of data in MRTG. 4. The problem started AFTER I rebooted the system after the update, so the reboot might have possibly allowed some settings to take effect with regards to the server's encoding. Maybe Centos 5.3 went from an EN_US language default to UTF8 default? If this is indeed the case, how would I possible change the interface/shell language settings back to the English one, since I don't typically need to input non-English characters nor view them in shell? I've added a LANG='en_US' and export LANG line in /etc/profile but it doesn't seem to be doing anything. Do I need a reboot for it to work like I am guessing based on #4 above? Thanks!