mariadb-install-db was added in MariaDB 10.4.6. mariadb-install-db is a symlink to mysql_install_db, the client statically linked to the embedded server. In MariaDB 10.5 mariadb-install-db will be the main command and mysql_install_db will be a symlink to mariadb-install-db.

This is part of an effort to prefix all mariadb- commands with mariadb- instead of mysql-, while still keeping the old commands around to not break any existing scripts.

See mysql_install_db for details.