我刚搬到另一个国家（纳米比亚到荷兰），由于某种原因 sudo apt-get update 停止工作并出现错误（我对 Ubuntu 很陌生）
Hit:1 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:2 http://repo.steampowered.com/steam precise InRelease
Get:3 http://na.archive.ubuntu.com/ubuntu xenial InRelease [4,618 B]
Err:3 http://na.archive.ubuntu.com/ubuntu xenial InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Hit:4 https://cli-assets.heroku.com/branches/stable/apt ./ InRelease
Get:5 http://na.archive.ubuntu.com/ubuntu xenial-updates InRelease [4,618 B]
Err:5 http://na.archive.ubuntu.com/ubuntu xenial-updates InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Hit:6 https://download.sublimetext.com apt/stable/ InRelease
Get:7 http://na.archive.ubuntu.com/ubuntu xenial-backports InRelease [4,618 B]
Err:7 http://na.archive.ubuntu.com/ubuntu xenial-backports InRelease
Clearsigned file isn't valid, got …apt ×1