ubuntu 16.04版本出现安装或者更新软件时网址链接error的问题

Get:1 http://mirrors.sohu.com/ubuntu xenial InRelease [8 B]
Err:1 http://mirrors.sohu.com/ubuntu xenial InRelease
  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:2 http://mirrors.sohu.com/ubuntu xenial-updates InRelease [8 B]
Err:2 http://mirrors.sohu.com/ubuntu xenial-updates InRelease
  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:3 http://mirrors.sohu.com/ubuntu xenial-backports InRelease [8 B]
Err:3 http://mirrors.sohu.com/ubuntu xenial-backports InRelease
  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:4 http://mirrors.sohu.com/ubuntu xenial-security InRelease [8 B]
Err:4 http://mirrors.sohu.com/ubuntu xenial-security InRelease
  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Fetched 32 B in 0s (156 B/s) 
Reading package lists... Done
E: Failed to fetch http://mirrors.sohu.com/ubuntu/dists/xenial/InRelease  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Failed to fetch http://mirrors.sohu.com/ubuntu/dists/xenial-updates/InRelease  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Failed to fetch http://mirrors.sohu.com/ubuntu/dists/xenial-backports/InRelease  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Failed to fetch http://mirrors.sohu.com/ubuntu/dists/xenial-security/InRelease  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Some index files failed to download. They have been ignored, or old ones used instead.

解决方法如下：

1. 打开系统设置，双击软件与更新；

　　

2. 修改Download from为Main Server ,然后点击关闭，弹出密码输入框，输入密码后确定弹出提示框，选择reload按钮。

3. 返回命令窗口，执行命令：sudo apt-get update或者sudo apt-get install ****;

执行成功。