title: git push... fatal: Unable to create master.lock: File exists
body: <p>Help!  When I try to do a <code>git push origin master</code> now, I get:</p>
  
  <pre><code>fatal: Unable to create '/home/ubuntu/workspace/.git/refs/remotes/origin/master.lock': File exists.
  If no other git process is currently running, this probably means a
  git process crashed in this repository earlier. Make sure no other git
  process is running and remove the file manually to continue.
  </code></pre>
  
  <p>Of course, I've found other similar questions (e.g. <a href="https://stackoverflow.com/questions/9282632/git-index-lock-file-exists-when-i-try-to-commit-but-cannot-delete-the-file">here</a>), but the upvoted answers in there merely suggest deleting the offending file... but the file does not exist!</p>
  
  <p>I fear that this is happening after I recently tried to clear some space using the following:</p>
  
  <pre><code>$ sudo git reflog expire --all --expire=now
  $ sudo git gc --prune=now --aggressive
  </code></pre>
  
  <p>Could that be the cause?  Any suggestions for a fix?</p>