ubuntu server命令行下自动选择最快的源

ubuntu桌面选择图形界面很简单，设置下就行，但是安装了ubuntu server字符界面就要自己来配置了

在sources.llist中加入

deb mirror://mirrors.ubuntu.com/mirrors.txt bionic main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-backports main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-proposed main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-security main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-updates main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt bionic main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt bionic-backports main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt bionic-proposed main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt bionic-security main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt bionic-updates main restricted universe multiverse

其中bionic是版本代号，替换成当前使用的版本