备份原有的CentOS-Base.repo备份为CentOS-Base.repo.bak
进入cd /etc/yum.repos.d
mv CentOS-Base.repo CentOS-Base.repo.bak
删除文件 CentOS-Base.repo
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.163.com/.help/CentOS7-Base-163.repo
yum clean all
yum makecache
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