在Windows系统中开启Linux子系统功能，安装Debian，安装完成后设置用户密码，然后使用用户密码sudo su到root用户，passwd设置root密码。然后使用apt update检查更新。这个时候发现检查很慢。
所以就想到了更换软件源。cd到/etc/apt/sources.list
deb http://deb.debian.org/debian stretch main
deb http://deb.debian.org/debian stretch-updates main
deb http://security.debian.org/debian-security/ stretch/updates main
deb http://ftp.debian.org/debian stretch-backports main
草（中日双语），怪不得这么慢，感情用的是官方源。
使用vim更改sources.list的内容
deb http://mirrors.aliyun.com/debian stretch main contrib non-free
deb http://mirrors.aliyun.com/debian stretch-proposed-updates main contrib non-free
deb http://mirrors.aliyun.com/debian stretch-updates main contrib non-free
deb-src http://mirrors.aliyun.com/debian stretch main contrib non-free
deb-src http://mirrors.aliyun.com/debian stretch-proposed-updates main contrib non-free
deb-src http://mirrors.aliyun.com/debian stretch-updates main contrib non-free
deb http://mirrors.aliyun.com/debian-security/ stretch/updates main non-free contrib
deb-src http://mirrors.aliyun.com/debian-security/ stretch/updates main non-free contrib
deb http://mirrors.aliyuncs.com/debian stretch main contrib non-free
deb http://mirrors.aliyuncs.com/debian stretch-proposed-updates main contrib non-free
deb http://mirrors.aliyuncs.com/debian stretch-updates main contrib non-free
deb-src http://mirrors.aliyuncs.com/debian stretch main contrib non-free
deb-src http://mirrors.aliyuncs.com/debian stretch-proposed-updates main contrib non-free
deb-src http://mirrors.aliyuncs.com/debian stretch-updates main contrib non-free
deb http://mirrors.aliyuncs.com/debian-security/ stretch/updates main non-free contrib
deb-src http://mirrors.aliyuncs.com/debian-security/ stretch/updates main non-free contrib
之后
apt clean all
apt update #检查更新
apt upgrade #更新已安装的软件包
顺带一提，Windows下的Linux子系统目录在C:\Users\~\AppData\Local\Packages\根据Debian或Ubuntu系统的不同此级目录会有不同\LocalState\rootfs
参考资料：https://yq.aliyun.com/articles/533974?tdsourcetag=s_pctim_aiomsg
