FYI on PHP 5.5 we saw a lot of defunt rrdtool proceeses (1 for every image created in the browser). If you see this there are a couple of fixes/work-around:

1. Fix it in observium, open ./includes/rrdtool.inc.php and change  function rrdtool_pipe_close(&$rrd_process, &$rrd_pipes) to function rrdtool_pipe_close($rrd_process, &$rrd_pipes)
   
2. downgrade to PHP 5.4

Seems to be caused by https://bugs.php.net/bug.php?id=69014

Regards,

Gerwin Krist