title: sudo on Mac: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set
body: <p>I accidentally ‘ruined’ the filesystem’s permission structure by running <code>chown Andy:staff /usr/bin</code> on my Mac.
  Now <code>sudo</code>raises an error:
  <code>sudo: /usr/bin/sudo must be owned by uid 0 and have the setui bit set</code></p>
  <p>I tried the most popular method online: <code>chown root:root /usr/bin/sudo &amp;&amp; chmod 4755 /usr/bin/sudo</code>
  But the shell said that root is an illegal user group.
  I do NOT want to reinstall the OS, so is there a way to fix this? Can anybody help me? Thanks!</p>