title: Change ownership of linux directory
body: <p>Hi I'm very new to Linux..</p>
  
  <p>Once I have changed ownership of <code>/usr</code> my <code>sudo</code> command failed working ..</p>
  
  <p>Once I changed ownership of <code>/var</code> some other things broke ..</p>
  
  <p>1: I just want to know which are folders where one should never change it's default ownership..</p>
  
  <p>2:   what if someone gets <code>permission_denied</code> for <code>/var</code> during installing some packages .. <code>chmod</code> or <code>chown</code> should be used ... </p>