After installing mariadb, run mysql_secure_installation
According to the instructions ( https://mariadb.com/kb/en/mariadb/mysql_secure_installation/ ) you can choose which actions to do (the same I usually do by hand one by one, plus a few more), so it seems safe if you know what you are doing.
For the general instructions, should we suggest to run in unattended mode in default ClearOS installs?
"mysql_secure_installation --use-default" (according to https://dev.mysql.com/doc/refman/5.7/en/mysql-secure-installation.html ), if the mysql/mariadb is equal or newer to 5.7.4.
(Edited to raise priority from 3 to 2)