title: apt update error: The repository 'http://us.archive.ubuntu.com/ubuntu saucy Release' does not have a Release file
body: <p>I run "sudo apt -y update" on my Ubuntu 16.04 server, but I got the following error:</p>
  
  <pre><code># apt -y update                    
  Reading package lists... Done                                                                                                       
  E: The repository 'http://us.archive.ubuntu.com/ubuntu saucy Release' does not have a Release file.
  N: Updating from such a repository can't be done securely, and is therefore disabled by default.
  N: See apt-secure(8) manpage for repository creation and user configuration details.
  E: The repository 'http://us.archive.ubuntu.com/ubuntu saucy-updates Release' does not have a Release file.
  N: Updating from such a repository can't be done securely, and is therefore disabled by default.
  N: See apt-secure(8) manpage for repository creation and user configuration details.
  root@yuyue-HP-Pro-3380-MT:/var/lib/apt# apt -y update
  Get:1 http://cn.archive.ubuntu.com/ubuntu xenial InRelease [132 B]
  Err:1 http://cn.archive.ubuntu.com/ubuntu xenial InRelease                                                                          
    Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
  Get:2 http://cn.archive.ubuntu.com/ubuntu xenial-updates InRelease [132 B]                                                          
  Err:2 http://cn.archive.ubuntu.com/ubuntu xenial-updates InRelease                                                                  
    Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
  Get:3 http://cn.archive.ubuntu.com/ubuntu xenial-backports InRelease [132 B]                                                        
  Err:3 http://cn.archive.ubuntu.com/ubuntu xenial-backports InRelease                                                                
    Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
  Ign:4 http://us.archive.ubuntu.com/ubuntu saucy InRelease                                                                           
  Hit:5 http://security.ubuntu.com/ubuntu xenial-security InRelease
  Ign:6 http://us.archive.ubuntu.com/ubuntu saucy-updates InRelease
  Err:7 http://us.archive.ubuntu.com/ubuntu saucy Release
    404  Not Found [IP: 2001:67c:1562::16 80]
  Err:8 http://us.archive.ubuntu.com/ubuntu saucy-updates Release
    404  Not Found [IP: 2001:67c:1562::16 80]
  Reading package lists... Done
  E: The repository 'http://us.archive.ubuntu.com/ubuntu saucy Release' does not have a Release file.
  N: Updating from such a repository can't be done securely, and is therefore disabled by default.
  N: See apt-secure(8) manpage for repository creation and user configuration details.
  E: The repository 'http://us.archive.ubuntu.com/ubuntu saucy-updates Release' does not have a Release file.
  N: Updating from such a repository can't be done securely, and is therefore disabled by default.
  N: See apt-secure(8) manpage for repository creation and user configuration details.
  </code></pre>
  
  <p>What could the reason be? How can I fix this problem? Thank you!</p>