How to set slow query log in MariaDB my.cnf?
You said you added this

log_slow_queries = 1
long_query_time = 1
log-slow-queries = /var/log/mysql/slow_query.log
log_queries_not_using_indexes


That's the old way MySQL 5.0 sets the slow query log.

To activate the slow query log for MySQL 5.6 and MariaDB, you must use the following


slow_query_log
slow_query_log_file


Therefore, you need this in my.cnf

slow_query_log = 1
long_query_time = 1
slow_query_log_file = /var/log/mysql/slow_query.log
log_queries_not_using_indexes