http://mirrors.163.com/centos/6/os/i386/repodata/repomd.xml: [Errno 14] PYCURL ERROR 6 - "Couldn't resolve host 'mirrors.163.com'"

Trying other mirror.

Error: Cannot retrieve repository metadata (repomd.xml) for repository: base. Please verify its path and try again

实际上是DNS问题

vi /etc/resolv.conf
nameserver 221.130.33.52
nameserver 168.95.1.1

yum update
解决