I just updated MariaDB to 5.5.40 and noticed that on CentOS 7, the files download from DirectAdmin is specific for CentOS 6 which is actually works fine on CentOS 7. (Something like -> MariaDB-5.5.40-centos6-x86_64-shared.rpm)
However, I found that MariaDB also released files for CentOS 7 here...