yum更新，docker安装

备份

cd /etc/yum.repos.d/

mkdir repo_bak

mv *.repo repo_bak/

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安装wget(若已安装了wget，则跳过此步

wget -V

yum install wget -y

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下载新的CentOS-Base.repo 到/etc/yum.repos.d/

wget http://mirrors.aliyun.com/repo/Centos-7.repo

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yum clean all 清除缓存，运行 yum makecache 生成新的缓存

yum clean all

yum makecache

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安装EPEL（Extra Packages for Enterprise Linux ）源

yum install -y epel-release

再次运行yum clean all 清除缓存，运行 yum makecache 生成新的缓存

查看启用的yum源和所有的yum源

yum repolist enabled

yum repolist all

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更新yum

yum -y update

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https://www.cnblogs.com/qgc1995/archive/2018/08/29/9553572.html