title: Installing R from CRAN Ubuntu repository: No Public Key Error
body: <p>I am on R version 2.13 and would like to update to a newer version in order to use some packages that depend on R>= 2.14. </p>
  
  <p>I have the line to my sources.list file as found described <a href="http://cran.r-project.org/bin/linux/ubuntu/" rel="noreferrer">here</a>.  I then navigate to the terminal and type:</p>
  
  <pre><code>sudo apt-get update
  </code></pre>
  
  <p>and get the following error when trying to update R on the CRAN mirror closest to me:</p>
  
  <blockquote>
    <p>Reading package lists... Done</p>
    
    <p>W: GPG error: <a href="http://lib.stat.cmu.edu" rel="noreferrer">http://lib.stat.cmu.edu</a> oneiric/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 51716619E084DAB9</p>
  </blockquote>
  
  <p>Any idea how to debug this error?</p>