#mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
#cd /etc/yum.repos.d/
#wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
#mv CentOS6-Base-163.repo CentOS-Base.repo
#yum clean all
#yum makecache
#yum update
在yum makecache支行，报一对错误：
http://mirrors.163.com/centos/6/addons/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found"
Trying other mirror.
http://mirror.centos.org/centos/6/addons/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found"
Trying other mirror.
我看了/etc/resolv.conf里面的几个DNS地址，都可以ping通，完全搞不明白要怎么办，求解答？
原因是，
http://mirrors.163.com/centos/6/addons/x86_64/repodata/repomd.xml
和
http://mirror.centos.org/centos/6/addons/x86_64/repodata/repomd.xml
确实不存在，可能被更新掉了。解决办法是，
找到可用的URL替换之，或者把相应的.repo文件中的项整个注释掉
。这里我采用后者。
例如，在CentOS-Base-163.repo中，注释掉整个addon项
#[addons]#name=CentOS-$releasever - Addons - 163.com#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons#baseurl=http://mirrors.163.com/centos/$releasever/addons/$basearch/#gpgcheck=1#pgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5