I’ve been scratching my head over this. Adminer runs fine on the many Ubuntu systems I’ve installed it on (with the exception of one), but everytime I use Centos, I get this error. Turns out, it’s a permissions issue. If you are getting this error related to Adminer or other php programs that use a CSRF token, check your php sessions folder. If you are not sure, put in a php file, and it will list your sessions location. Usually something like /var/lib/php/session. Make sure that folder exists, and that the group is set the same as your web server. So if that’s Nginx on Ubuntu that would be www-data. Centos it would be nginx. Apache, apache, and so forth. Then change the group and the location for your system and run the following:
chgrp www-data /var/lib/php/session
Adminer should be happy now.