title: git: Error: Another active Homebrew process is already in progress
body: <p>When I try to do anything with <code>Homebrew</code>, I get the following error and don't know how to resolve it.
  I run: <code>brew update</code></p>
  
  <p>I get the following error message:</p>
  
  <pre><code>/usr/local/Homebrew/Library/Homebrew/utils/lock.sh: line 19:/usr/local/var/homebrew/locks/update: Permission denied
      -e:1:in 'initialize': Bad file descriptor (Errno::EBADF)
          from -e:1:in 'new'
          from -e:1:in '&lt;main&gt;'
      Error: Another active Homebrew process is already in progress. 
      Please wait for it to finish or terminate it to continue.
  </code></pre>