Yum repository mirror for old CentOS' versions
Answer:
Most CentOS' mirrors don't host full mirror of Yum repository for all versions of CentOS. If you are using older version of CentOS, you might one-day found the yum update is broken since the mirror no longer contains the files you needed.
In this case, you can modify the file /etc/yum.repos.d/CentOS-Base.repo and change all paths point to the following:
..
baseurl=http://vault.centos.org/...
..Then do a yum update to reflect the changes.
