vmcore-dmesg : Missing the log_buf symbol

Hello, I have generated a vmcore file using kdump and are now supposed to analyze it. First would be getting the dmesg logs from the core dump. This should be done with: vmcore-dmesg vmcore This however does not seem to work as there is the error: Missing the log_buf symbol Could someone know how to get around this error? Any help would be much appreciated. Cheers, David.