NOTE: You need an instance of the memcached server running in order to carry out this test. The instructions here assume it is running on localhost on the default port. This test requires access to temporarily modify Moodle code. 1. In server settings, edit config.php to add the following (after or instead of any existing session handler code): $CFG->session_handler_class = '\core\session\memcache'; $CFG->session_memcache_save_path = '127.0.0.1:11211,localhost:11211'; $CFG->session_memcache_acquire_lock_timeout = 120; Note that this has a list of 2 memcache servers which are actually both the same server. If you have 2 real servers feel free to use different ones, but the same one twice is enough to demonstrate the bug. 2. Visit your Moodle and log in. Click around for a couple of pages (e.g. in the admin screens). EXPECTED: You remain logged in (the session is working). 3. Edit the config.php to change the line to: $CFG->session_memcache_save_path = 'tcp://127.0.0.1:11211,tcp://localhost:11211'; This is the 'raw' format which some people might mistakenly use. 4. Visit Moodle again. EXPECTED: You should get a session configuration error. If you have debugging on, you'll see the explanation that you need to not include tcp:// in the variable.