If you need to reinstall MariaDB on DirectAdmin server. Here is how you can do it.

Dump MySQL tables

First, make sure to dump all existing databases

cd /usr/local/directadmin/custombuild/
./build update
./build mysql_backup

You should have sufficient free disk space for it and it might take a while to dump big databases. You should never skip this step.

Copy MySQL config file 

If you have customized the file /etc/my.cnf you will need to copy it to a safe place:

\cp -p /etc/my.cnf /etc/my.cnf~poralix

Remove existing MariaDB

On CentOS and CloudLinux servers run the following command:

rpm -qa | grep mariadb -i | xargs rpm -e --noscripts

Here you might need to kill a running copy of a SQL-server.

Rename /var/lib/mysql/

Later after you re-install the SQL-server you can remove the old data directory, but now it would be better to rename folder.

\mv /var/lib/mysql /var/lib/mysql.moved

Re-install /etc/my.cnf

It you have a customized version of settings for SQL-server it is the right time to install it.

\cp -p /etc/my.cnf~poralix  /etc/my.cnf

Re-install MariaDB:

Now we do a fresh installation of a SQL-server:

cd /usr/local/directadmin/custombuild/
./build update
./build mysql

As soon as the installation complete we need to set a password.

Set root's password

By default when installing MariaDB, there might be empty root's password, so we need to set it. It can be done with a help of mysql_secure_installation:

mysql_secure_installation

Follow the steps, and answer Yes, when asked whether or not you want to set a password.

Recover mysql database

First we recover mysql database to restore all users accounts:

cd /usr/local/directadmin/custombuild/mysql_backups
mysql mysql -p < mysql.sql

Enter the root's password when asked.

Restart SQL-server:

systemctl restart mysqld

Restore other databases

And now we can restore all databases:

cd /usr/local/directadmin/custombuild/mysql_backups
wget http://files1.directadmin.com/services/all/mysql/restore_sql_files.sh
chmod 755 restore_sql_files.sh
./restore_sql_files.sh

That's it.

https://help.poralix.com/articles/how-to-reinstall-mariadb-on-directdamin-server