一：將現有的yum源解除安裝

# rpm -qa yum

# rpm -qa | grep yum | xargs rpm -e --nodeps #這一步一定要執行，而且要將所有的元件解除安裝掉，如果解除安裝不乾淨，後面安裝會有問題

# rpm -qa yum

二、從centos官網上下載和yum有關的rpm包

contos7:

 # wget http://mirror.centos.org/centos/7/os/x86_64/Packages/yum-3.4.3-150.el7.centos.noarch.rpm  # wget http://mirror.centos.org/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm  # wget http://mirror.centos.org/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-40.el7.noarch.rpm   

contos6:

http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-3.2.29-81.el6.centos.noarch.rpm http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-metadata-parser-1.1.2-16.el6.x86_64.rpm http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm  

我的是6.5，但這個rpm包軟體裡面有，分別是：

yum-3.2.29-40.el6.centos.noarch.rpm

yum-metadata-parser-1.1.2-16.el6.x86_64.rpm

yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm

三：安裝

#  rpm -ivh yum-* #安裝

# rpm -qa yum #檢視是否已經安裝上

1: 

 #  rm -f /etc/yum.repos.d/*  

contos7:

# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo 

contos6:

#wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo 

# yum clean all