1. rm -rf /etc / yum.repos.d /*
    2. curl -o /etc /yum. repos.d/CentoS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repoyum clean all
    3. yum repolist all
    4. yum -y install epel-release
    5. yum -y install bash-completion vim tree net-tools bind-utils