所以我在我的大学网络上，这要求我在开始使用互联网之前登录浏览器。我成功地这样做了，但是在干净安装 Ubuntu 时，当我尝试这样做时sudo apt update，我得到以下输出：
$ sudo apt update
Get:1 http://in.archive.ubuntu.com/ubuntu xenial InRelease [2,847 B]
Err:1 http://in.archive.ubuntu.com/ubuntu xenial InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:2 http://security.ubuntu.com/ubuntu xenial-security InRelease [2,854 B]
Err:2 http://security.ubuntu.com/ubuntu xenial-security InRelease
...
Get:3 http://in.archive.ubuntu.com/ubuntu xenial-updates InRelease [2,855 B]
Err:3 http://in.archive.ubuntu.com/ubuntu xenial-updates InRelease
...
Get:4 http://in.archive.ubuntu.com/ubuntu xenial-backports InRelease [2,857 B]
Err:4 http://in.archive.ubuntu.com/ubuntu xenial-backports InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
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