Here is my error;
Starting process with log file at /var/cpanel/logs/mysql_upgrade.20171216-091130/upgrade_mysql_with_status.log
Obtained version information from system.
Proceeding with MySQL/MariaDB upgrade despite the following: Normal: The selected MariaDB version (10.1) is more than one generation newer than the currently installed version. The upgrade process will iterate over each intervening version to ensure tables are upgraded appropriately. Critical: The update could not reach the MySQL server to check for the presence of pre-4.1-style MySQL passwords. This issue could also hinder mysql_upgrade's ability to run, which could potentially leave MySQL in an unusable state if you proceed.
Obtained version information from system.
(XID njr8zz) The system received an error from the “MySQL” database “mysql”: 23 (Out of resources when opening file './mysql/user.MYD' (Errcode: 24 - Too many open files))
Obtained version information from system.
Proceeding with MySQL/MariaDB upgrade despite the following: Normal: The selected MariaDB version (10.1) is more than one generation newer than the currently installed version. The upgrade process will iterate over each intervening version to ensure tables are upgraded appropriately. Critical: The update could not reach the MySQL server to check for the presence of pre-4.1-style MySQL passwords. This issue could also hinder mysql_upgrade's ability to run, which could potentially leave MySQL in an unusable state if you proceed.
How can this be fixed?
If you are running Cpanel 11.66 version then you can upgrade MariaDB to 10.2 otherwise 10.1 is the highest in 11.64 version of cpanel
so check the versions of cpanel you are running on the right top corner of WHM once you logged in with root and then move further.