yum源更换为阿里云源

#首先备份/etc/yum.repos.d/CentOS-Base.repo
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
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#进入yum源配置文件所在文件夹
cd /etc/yum.repos.d/
​
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#下载阿里云的yum源配置文件，放入/etc/yum.repos.d/(操作前请做好相应备份)
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
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#清除旧缓存
yum clean all
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#运行yum makecache生成缓存
yum makecache