CentOS[6-8]更换阿里云yum及epel源

### yum源

备份官方yum源

cd /etc/yum.repo.d && mkdir repo.bak && mv ./*.repo ./repo.bak

更新阿里云yum源

CentOS 6

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-6.repo
或者
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
或者
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo

CentOS 8

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-8.repo
或者
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-8.repo

### epel源

更新阿里云epel源

CentOS6

wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo

CentOS7

wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo

CentOS8

yum install -y https://mirrors.aliyun.com/epel/epel-release-latest-8.noarch.rpm
sed -i 's|^#baseurl=https://download.fedoraproject.org/pub|baseurl=https://mirrors.aliyun.com|' /etc/yum.repos.d/epel*
sed -i 's|^metalink|#metalink|' /etc/yum.repos.d/epel*

### 更新缓存

yum clean all
yum makecache