title: Extract gnutls library files of tar.xz and tar.lz for ubuntu 10.04 LTS
body: <p>I am very new to linux platform and I want to extract gnutls for ubuntu. If I do,</p>
  
  <pre><code>$ls
  </code></pre>
  
  <p>then, it will show these files below.</p>
  
  <pre><code>gnutls-3.2.1.tar.lz
  gnutls-3.2.1.tar.lz.sig
  gnutls-3.2.1.tar.xz
  gnutls-3.2.1.tar.xz.sig
  </code></pre>
  
  <p>When I give command,</p>
  
  <pre><code>$ tar -xvf gnutls-3.2.1.tar.xz
  </code></pre>
  
  <p>I get output,</p>
  
  <pre><code>tar: xz: Cannot exec: No such file or directory
  tar: Error is not recoverable: exiting now
  tar: Child returned status 2
  tar: Exiting with failure status due to previous errors
  </code></pre>
  
  <p>I want to extract these files.</p>
  
  <ol>
  <li>Why there are two types of formats given? - xz and lz</li>
  <li>Why there are signature files? - .sig
  How to verify it? I tried to verification by <code>gpgv &lt;filename&gt;.sig</code> command, it says public key   is not found.</li>
  <li>I need a separate utility package? I saw one, 'xz-utils_4.999' but it is <strong>beta</strong>. 
  <a href="http://manpages.ubuntu.com/manpages/lucid/man1/xz.1.html" rel="noreferrer">http://manpages.ubuntu.com/manpages/lucid/man1/xz.1.html</a></li>
  <li>Any other stable utility package? From where and how can I download it?</li>
  </ol>