recentsessionlocks debugging clashes with readonly sessions

1) Configure readonly sessions: $CFG->enable_read_only_sessions = true; 2) As part of this you will need to configure MUC to store session caches in a place outside the session, ie make the default Session store 'file'. E.g. Go to admin > plugins > caching > configuration and scroll to the bottom. Click 'edit mappings' Change sesssion to 'default file store for application caches' 3) Also configure session lock debugging: $CFG->debugsessionlock = 100; 4) Tail the error logs in a new terminal window: sudo tail -f /var/log/apache2/error.log 5) Visit the dashboard and some other random pages to fill the recent session lock list 6) copy attached php file  MDL-68983 -recentsessionlocks.php to your site root and visit / MDL-68983 -recentsessionlocks.php 7) Confirm there are NOT any errors in the logs like this: The following SESSION params were either added, or were updated. SESSION key: recentsessionlocks