If for whatever reason, you are stuck with the now EOL version of the CentOS operating system, you can no longer run yum upgrade successfully. Running yum upgrade in CentOS 6 will yield the following results:
Setting up Upgrade Process
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
Eg. Invalid release/repo/arch combination/
removing mirrorlist with no valid mirrors: /var/cache/yum/x86_64/6/base/mirrorlist.txt
Error: Cannot retrieve repository metadata (repomd.xml) for repository: base. Please verify its path and try again
Use the CentOS Vault repository :-
The CentOS Vault repositories have been around for a long time and allow you to stick to a specific CentOS x.y release even while newer ones are available. Now that there will be no newer 6.x, you can simply point your yum repository configuration to the latest 6.x that will ever be, which is 6.10.
To use the Vault repository, set up its repo configuration instead of the now defunct repositories configuration:
curl https://www.getpagespeed.com/files/centos6-eol.repo --output /etc/yum.repos.d/CentOS-Base.repo
