title: PHP Sessions Expiring Unexpectedly
body: <p>I'm at a loss here.  I've got a specific group of users upstairs whose sessions seem to expire completely randomly.  It's not just when they leave the site sitting for a while, it can expire while they're browsing around.  For me and most of our users everything works just fine.  It's not a browser issue, we've got people in FF and all IE versions that both function correctly, and people in FF and IE that don't work.</p>
  
  <p>My <code>gc_maxlifetime</code> is at <code>43200</code> and the garbage collection is a crazy low <code>1/1000</code> (not that that should matter). Is it possible there's something else running on the server that's randomly deleting some of our sessions?  What should I check?  That still wouldn't explain why only this specific group seems to be affected.</p>
  
  <p>I have a few Session settings that are different from the default:</p>
  
  <pre><code>session.gc_maxlifetime = 43200
  session.gc_divisor = 1000
  session.save_path = /var/lib/php/session
  session.use_only_cookies = Off
  session.bug_compat_42 = Off
  </code></pre>
  
  <p>The first three I'm not worried about, but could the last two be causing this behavior?  I don't actually ever send cookies through the URL, so I have no good reason for having use_only_cookies off.  I have no guarantees that the misfits who made this app before I got here didn't exploit the <code>bug_compat_42</code> thing to set session variables, but again, I would expect an issue with that to be less random.</p>
  
  <p>Edit:</p>
  
  <p>On further investigation, I've found that the Session is not being destroyed at all, but the end-user is getting a new session ID.  The old session still exists intact on the server, but a new one is randomly started while they're browsing.</p>