(1) when installing or updating the software by Yum, you maybe come across the unexpected exit from the Yum tools and then report some errors which indicate some incorrect Yum sources! It maybe result from some obsolete Yum sources,so you'd better delete these problematic sources from /etc/yum.conf or /etc/yum.repos.d/ .
(2)pub－key,some Yum sources need to authorize and you should find pub－key which belongs to the source and import the pub-key: rpm －－import pub－key