It's not officially possible to migrate from MySQL 8.0 to MariaDB 10.3 in cPanel, since the two versions on a storage level are by no means compatible.
If you however require to change from MySQL 8.0 to MariaDB 10.3, this guide explains how to do it.
Note: Please keep in mind, this is by no means supported by cPanel. Attempting this is at your own risk.
Since the underlying file format differs between MySQL 8.0 and MariaDB 10.3, it requires that you back up all your databases, since they have to be restored after the MariaDB installation.
1: Perform a backup of your databases
To perform a backup of your databases, however, we want to skip a few databases, namely mysql, sys, information_schema and performance_schema, and then we dump it. We'll use a script from stackoverflow below (slightly modified):
Your databases are now stored in
2: Uninstall MySQL packages
Next we'll uninstall MySQL 8.0 packages, it can be done quite simply with yum:
Simply press
Now we also remove the /var/lib/mysql:
3: Change the mysql-version in cpanel.config
We now want to change from MySQL 8.0 to MariaDB 10.3 in the
4: Install MariaDB 10.3
We can simply use whmapi1 to start an "upgrade":
It will return an upgrade_id, such as mysql_upgrade.20200731-204729
We can use this to check the progress:
You'll eventually see:
While you can execute
5: Reset the MySQL root password
Some functions will not really work correctly without resetting the MySQL root password, I don't know the exact reason, but resetting the password makes all functions work again:
6: Restore databases
Restoring the databases will be as simple as running:
However, this will only restore the databases, not the users and the grants for the users. We'll do this next!
7: Restore user grants
cPanel keeps users (including password hashes) and grants in some map files, we can use these files to restore the grants for all our users:
And we're done 
If you however require to change from MySQL 8.0 to MariaDB 10.3, this guide explains how to do it.
Note: Please keep in mind, this is by no means supported by cPanel. Attempting this is at your own risk.
Since the underlying file format differs between MySQL 8.0 and MariaDB 10.3, it requires that you back up all your databases, since they have to be restored after the MariaDB installation.
1: Perform a backup of your databases
To perform a backup of your databases, however, we want to skip a few databases, namely mysql, sys, information_schema and performance_schema, and then we dump it. We'll use a script from stackoverflow below (slightly modified):
Bash:
mysql -ANe "SELECT schema_name FROM information_schema.schemata WHERE schema_name NOT IN ('mysql','information_schema','performance_schema', 'sys')" > databases.txt
DBLIST=""
for DB in `cat databases.txt` ; do DBLIST="${DBLIST} ${DB}" ; done
MYSQLDUMP_OPTIONS="--routines --triggers --single-transaction"
mysqldump ${MYSQLDUMP_OPTIONS} --databases ${DBLIST} > all-dbs.sqlall-dbs.sql2: Uninstall MySQL packages
Next we'll uninstall MySQL 8.0 packages, it can be done quite simply with yum:
Bash:
yum remove mysql-community-*y to confirm the uninstall.Now we also remove the /var/lib/mysql:
Bash:
rm -rf /var/lib/mysqlWe now want to change from MySQL 8.0 to MariaDB 10.3 in the
cpanel.config file.
Bash:
sed -i 's/mysql-version=8.0/mysql-version=10.3/g' /var/cpanel/cpanel.configWe can simply use whmapi1 to start an "upgrade":
Bash:
whmapi1 start_background_mysql_upgrade version=10.3We can use this to check the progress:
Bash:
tail -f /var/cpanel/logs/mysql_upgrade.20200731-204729/unattended_background_upgrade.log
Code:
mysql restarted successfully.
MariaDB upgrade completed successfullymysql and it will give you the MariaDB prompt, there's a few functions that doesn't work, we'll do that by resetting the password.5: Reset the MySQL root password
Some functions will not really work correctly without resetting the MySQL root password, I don't know the exact reason, but resetting the password makes all functions work again:
Bash:
whmapi1 set_local_mysql_root_password password=superSecurePasswordRestoring the databases will be as simple as running:
Bash:
mysql < all-dbs.sql7: Restore user grants
cPanel keeps users (including password hashes) and grants in some map files, we can use these files to restore the grants for all our users:
Bash:
for user in $(ls /var/cpanel/users); do echo $user; /usr/local/cpanel/bin/restoregrants --db=mysql --cpuser=$user --all; done