一、CentOS 8停止更新后，大家使用yum安装程序的时候，会报这个错误：
CentOS Linux 8 - AppStream Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
二、解决方法：
打开终端，输入 su 命令切换 root 用户登录，然后使用下面的命令更新源：
sed -i -e "s|mirrorlist=|#mirrorlist=|g" /etc/yum.repos.d/CentOS-*
sed -i -e "s|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g" /etc/yum.repos.d/CentOS-*
- mirrorlist appstream download metadata internalmirrorlist appstream download metadata mirrorlist appstream internal错误 appstream download metadata centos download metadata failed adv-os appstream mirrorlist appstream错误centos8数据 mirrorlist unknown resolve方法 mirrorlist yum removing centos6 centos mirrorlist removing mirrors