第一步：确认你的系统版本
cat /etc/redhat-release 2
第二步：备份并替换 repo 文件
备份原有 repo
mkdir -p /etc/yum.repos.d/backup
mv /etc/yum.repos.d/*.repo /etc/yum.repos.d/backup/ 2>/dev/null || true
创建专用于 CentOS 7.6.1810 的 repo
cat > /etc/yum.repos.d/CentOS-Base.repo <<EOF
base
name=CentOS-7.6 - Base
baseurl=https://mirrors.aliyun.com/centos-vault/7.6.1810/os/\\$basearch/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/RPM-GPG-KEY-CentOS-7
enabled=1
updates
name=CentOS-7.6 - Updates
baseurl=https://mirrors.aliyun.com/centos-vault/7.6.1810/updates/\\$basearch/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/RPM-GPG-KEY-CentOS-7
enabled=1
extras
name=CentOS-7.6 - Extras
baseurl=https://mirrors.aliyun.com/centos-vault/7.6.1810/extras/\\$basearch/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/RPM-GPG-KEY-CentOS-7
enabled=1
centosplus
name=CentOS-7.6 - Plus
baseurl=https://mirrors.aliyun.com/centos-vault/7.6.1810/centosplus/\\$basearch/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/RPM-GPG-KEY-CentOS-7
enabled=0
EOF
第三步：清理缓存并测试
yum clean all
rm -rf /var/cache/yum
yum makecache
yum list installed | head -5 # 查看是否能读取包列表
yum install -y wget # 测试安装