更新yum爲國內yum源

su - root

cd /etc/yum.repos.d

mv /etc/yum.repos.d/

mv CentOS-Base.repo CentOS-Base.repo.bak

wget http://mirrors.sohu.com/help/CentOS-Base-sohu.repo

或者

wget http://mirrors.163.com/.help/CentOS6-Base-163.repo

mv CentOS-Base-sohu.repo CentOS-Base.repo

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*

更新完yum源後，建議更新一下，使操作立即生效

yum makecache

在執行最後一步，即yum makecache的時候，遇到錯誤：

Loaded plugins: fastestmirror

Repository base is listed more than once in the configuration

Repository updates is listed more than once in the configuration

Repository extras is listed more than once in the configuration

Repository centosplus is listed more than once in the configuration

Repository contrib is listed more than once in the configuration

Loading mirror speeds from cached hostfile

* addons: mirrors.163.com

* base: mirror.metrocast.net

* extras: mirror.beyondhosting.net

* fasttrack: centos.vipernetworksystems.com

* updates: centos.vipernetworksystems.com

http://mirrors.163.com/centos/6/addons/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404"

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"

Trying other mirror.

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

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 確實不存在，可能被更新掉了。解決辦法是，找到可用的URL替換之，或者把相應的.repo文件中的項整個註釋掉。這裏我採用後者。

例如，在CentOS-Base-163.repo中，註釋掉整個addon項

#[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

在CentOS-Base-sohu.repo中註釋掉下面的內容

#[addons]

#name=CentOS-$releasever - Addons - sohu.com

#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons

#baseurl=http://mirrors.sohu.com/centos/$releasever/addons/$basearch/

#gpgcheck=1

#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5CentOS-Base-sohu.repo

然後，再執行yum makecache。之後，yum就可以找到我要安裝的包了

yum upgrade

建議：不需要更新yum源，centos自己會找最近的yum安裝