title: sudo apt-get install xvfb
body: <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  The following package was automatically installed and is no longer required:
    libruby1.8
  Use 'apt-get autoremove' to remove them.
  The following extra packages will be installed:
    xserver-common
  The following NEW packages will be installed:
    xvfb
  The following packages will be upgraded:
    xserver-common
  1 upgraded, 1 newly installed, 0 to remove and 308 not upgraded.
  1 not fully installed or removed.
  Need to get 0 B/899 kB of archives.
  After this operation, 2,068 kB of additional disk space will be used.
  Do you want to continue [Y/n]? Y
  Setting up apt (0.8.16~exp5ubuntu13.2) ...
  gpg: symbol lookup error: /usr/local/lib/libreadline.so.6: undefined symbol: UP
  gpg: symbol lookup error: /usr/local/lib/libreadline.so.6: undefined symbol: UP
  dpkg: error processing apt (--configure):
   subprocess installed post-installation script returned error exit status 127
  Errors were encountered while processing:
   apt
  E: Sub-process /usr/bin/dpkg returned an error code (1)
  </code></pre>
  
  <p>Why I cannot install xvfb?</p>