work-around to get memcached going on the wiki
It appears that sometimes the folder /run/memcached/ is not created (for memcached.pid to live in) after a restart. the symptom is that users may not login to the wiki, with the error being a "session error."
There seems to be a problem with your login session; this action has been canceled as a precaution against session hijacking. Go back to the previous page, reload that page and then try again.
For the record, the work-around to get things going is
sudo chown memcached:memcached /run/memcached sudo systemctl restart memcached
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