centos7 执行yum命令 报错 已加载插件：fastestmirror, langpacks Loading mirror speeds from cached hostfile Could n

一、问题

已加载插件：fastestmirror, langpacks Loading mirror speeds from cached hostfile Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was 14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的错误"

二、原因

无法访问外网，需要更换访问的镜像源

三、解决方案

1、备份yum源

sudo cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.back

sudo cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.back

2、下载阿里云的 yum 源文件并替换本地 yum 源文件

# 下载 yum 源
sudo curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
# 清理缓存
sudo yum clean all
# 生成新的缓存
sudo yum makecache
# 更新yum
sudo yum update