Q:
I've recently updated to Red Hat Enterprise Linux 4.5 and I see the error message "EDAC k8 MC0: extended error code: ECC chipkill x4 error" in /var/log/messages. What does the error mean?

A:
Error Detection And Correction (EDAC) support for AMD Opteron CPUs was included in Red Hat Enterprise Linux 4 Update 5. The messages, found in /var/log/messages, usually means that the system has a hardware problem, although this is not always the case. Its possible that there is a hardware problem which simply wasn't known about because EDAC wasn't enabled prior to upgrading to Update 5. Some basic hardware checks, as discussed in the knowledgebase article below, can be used to determine whether this is a hardware problem.
http://kbase.redhat.com/faq/FAQ_80_7727.shtm

Another common cause of the errors is a broken EDAC implementation; a BIOS update may fix the problem. If there are no BIOS updates available, or the BIOS update doesn't solve the problem the blacklist the edac modules which will prevent them from loading. This will stop the errors from showing, but should only be done when confident that the hardware is not actually faulty.

# echo k8_edac >> /etc/hotplug/blacklist
# echo edac_mc >> /etc/hotplug/blacklist
# modprobe -r k8_edac edac_mc

Refer: http://kbase.redhat.com/faq/FAQ_85_11163.shtm