Drop database return "Error dropping database errno: 66" in MySQL

Consider:

DROP DATABASE db_name;
ERROR 1010 (HY000): Error dropping database (can't rmdir './db_name', errno: 66)

The problem is that I don't know where the file/directory is located - this file is missing in /usr/local/mysql/bin/...

How do I fix this issue?

mysql> drop database DB_NAME; 
ERROR 1010 (HY000): Error dropping database 
(can't rmdir './DB_NAME', errno: 66)

1. Find the database directory: mysql -e "select @@datadir" -> /usr/local/mysql/data/

2. Go to the DataBase folder: cd /usr/local/mysql/data/

3. Delete DB folder of the DB with the issue (in this case: sudo rm -rf DB_NAME)

If you are using XAMPP in OSX the data directory would be at

/Applications/XAMPP/xamppfiles/var/mysql