Thx but.. for unknown reason after the upgrade to 5.7 the mysql.user table contains mysql user only ... then if happen the solution is:
After upgrade restore the mysql user table from a previous backup;
run mysql_upgrade;
try to log mysql as a user root, if you cant use the skip-grant-tables...
In a plesk Onix after MySQL upgrade to 5.7.18 going to the admin panel I see the error:
ERROR: Zend_Db_Adapter_Exception: SQLSTATE[HY000] [1045] Access denied for user 'admin'@'localhost' (using password: YES)
Additionally, an exception has occurred while trying to report this error...