title: MySQL: Package 'mysql-server' has no installation candidate
body: <p>This error is being shown whenever I want to install any software via command line.
  Even if i try to install softwares which I know are present at the source from where I am downloading.</p>
  
  <p>Below is the full error message i am getting :</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Package mysql-server is not available, but is referred to by another package.
  This may mean that the package is missing, has been obsoleted, or
  is only available from another source
  
  E: Package 'mysql-server' has no installation candidate
  </code></pre>