How to start mariadb/mysql instances at boot?

I've got a file /etc/mysql/mysqld_multi_cls.cnf with everyting mariadb needs for multiple database instances. I can start these instances with the following command: sudo mariadbd-multi --defaults-file=/etc/mysql/mysqld_multi_cls.cnf start But I can't find a (neat) way to start these instances at boot. Adding the .cnf file in the /conf.d/ folder doesn't start the instance, unless I'm messing up unknowingly. The db is running on a Raspberry pi5, Raspberry Pi OS, which is Debian based. And I am quite unfamiliar/noob with Linux. After request, here is the .cnf file: # Configuration Settings for mysqld_multi , as well as separate instances. # [mysqld_multi] mysqld = /usr/bin/mariadbd-safe mysqladmin = /usr/bin/mariadb-admin [mysqld2] socket = /tmp/mysql.sock2 port = 3307 pid-file = /usr/local/mysql/mdb2/ansible-host1.pid2 datadir = /var/lib/mysql2 log-error = /var/log/mysql2/error.log log-bin = /var/log/mysql2/mdb2-mysql-bin.log server-id = 2 expire-logs-days = 72 sync_binlog = 1 innodb_flush_log_at_trx_commit = 1 innodb_flush_method = O_DIRECT binlog_format = mixed gtid_strict_mode = 1 [mysqld3] socket = /tmp/mysql.sock3 port = 3308 pid-file = /usr/local/mysql/mdb3/ansible-host1.pid3 datadir = /var/lib/mysql3 log-error = /var/log/mysql3/error.log log-bin = /var/log/mysql3/mdb3-mysql-bin.log server-id = 3 expire-logs-days = 64 sync_binlog = 1 innodb_flush_log_at_trx_commit = 1 innodb_flush_method = O_DIRECT binlog_format = mixed gtid_strict_mode = 1 [mysqld4] socket = /tmp/mysql.sock4 port = 3309 pid-file = /usr/local/mysql/mdb4/ansible-host1.pid4 datadir = /var/lib/mysql4 log-error = /var/log/mysql4/error.log log-bin = /var/log/mysql4/mdb4-mysql-bin.log server-id = 4 expire-logs-days = 64 sync_binlog = 1 innodb_flush_log_at_trx_commit = 1 innodb_flush_method = O_DIRECT binlog_format = mixed gtid_strict_mode = 1