title: Ubuntu 12.04 apt-get update GPG error
body: <p>my goal is upgrading Ubuntu 12.04 LTS to 14.04 LTS. I don't have running a surface, because it's only used as a issue tracking server. At first i wanted to update the current system.</p>
  
  <p>After <code>sudo apt-get update</code> i get this:</p>
  
  <pre><code>OK   http://archive.canonical.com precise Release.gpg
  OK   http://archive.canonical.com precise Release
  Hole:1 http://archive.ubuntu.com precise Release.gpg [198 B]
  OK   http://archive.canonical.com precise/partner Sources
  OK   http://archive.canonical.com precise/partner amd64 Packages
  Hole:2 http://archive.ubuntu.com precise-updates Release.gpg [198 B]
  OK   http://archive.canonical.com precise/partner i386 Packages
  Ign http://archive.canonical.com precise/partner TranslationIndex
  Hole:3 http://archive.ubuntu.com precise-security Release.gpg [198 B]
  OK   http://archive.ubuntu.com precise Release
  Ign http://archive.ubuntu.com precise Release
  Hole:4 http://archive.ubuntu.com precise-updates Release [49,6 kB]
  Ign http://archive.ubuntu.com precise-updates Release
  Hole:5 http://archive.ubuntu.com precise-security Release [49,6 kB]
  Ign http://archive.ubuntu.com precise-security Release
  W: GPG-Fehler: http://archive.ubuntu.com precise Release: Die folgenden Signaturen waren ungültig: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key &lt;ftpmaster@ubuntu.com&gt;
  W: GPG-Fehler: http://archive.ubuntu.com precise-updates Release: Die folgenden Signaturen waren ungültig: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key &lt;ftpmaster@ubuntu.com&gt;
  E: GPG-Fehler: http://archive.ubuntu.com precise-security Release: Die folgenden Signaturen waren ungültig: NODATA 2
  </code></pre>
  
  <p>After that i tried</p>
  
  <pre><code>sudo rm /var/lib/apt/lists/* -vf
  sudo apt-get update &amp;&amp; sudo apt-get upgrade
  </code></pre>
  
  <p>because i thought the error results in a wrong entry in my sources.list, but the course didn't change.</p>
  
  <p>Then i tried to get the key with</p>
  
  <pre><code>gpg --keyserver keyserver.ubuntu.com --recv 40976EAF437D05B5
  </code></pre>
  
  <p>which resulted in</p>
  
  <pre><code>gpg: requesting key 437D05B5 from hkp server keyserver.ubuntu.com
  gpgkeys: key 40976EAF437D05B5 not found on keyserver
  gpg: no valid OpenPGP data found.
  gpg: Total number processed: 0
  </code></pre>
  
  <p>At this point i don't know what to do anymore, hoping for your help!</p>
  
  <p>Greetings,
  vach</p>