title: can't install mongodb on ubuntu 16.10
body: <p>I'm trying to install mongodb by following this <a href="https://docs.mongodb.com/manual/tutorial/install-mongodb-on-ubuntu/" rel="nofollow noreferrer" title="manual">manual</a> (i'm using ubuntu 16.10) I've successfully installed mongodb before but I got an error  so i uninstalled mongodb.</p>
  
  <p>When I try to install it again i got this error when i enter <code>sudo apt-get install -y mongodb-org</code> on my terminal:</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  The following additional packages will be installed:
    mongodb-org-mongos mongodb-org-server mongodb-org-shell mongodb-org-tools
  The following NEW packages will be installed:
    mongodb-org mongodb-org-mongos mongodb-org-server mongodb-org-shell
    mongodb-org-tools
  0 upgraded, 5 newly installed, 0 to remove and 255 not upgraded.
  Need to get 66,7 MB of archives.
  After this operation, 269 MB of additional disk space will be used.
  WARNING: The following packages cannot be authenticated!
    mongodb-org-shell mongodb-org-server mongodb-org-mongos mongodb-org-tools
    mongodb-org
  E: There were unauthenticated packages and -y was used without --allow-unauthenticated
  </code></pre>