Saw error DBT-06006 when we tried to create a database by Database Configuration Assistant (DBCA).
[FATAL] [DBT-06006] Unable to create directory: (/oradata/ORCLCDB/).
CAUSE: Proper permissions are not granted to create the directory or there is no space left in the volume.
DBT-06006 means that the subdirectory you want to use for a database cannot be create at this moment, it could be a permission problem or the root directory does not exist.
In this case, we haven't created the root direcectory /oradata, so oracle was unable to create the subdirectory /oradata/ORCLCDB/ for this database to put data files.
To solve DBT-06006, we should make the directory /oradata before creating the database.
If there already has a base directory for data files, you may check the ownership and permission of the directory. Usually, it's owned by oracle and permission should be 775.
There's a complete procedure of installing and creating oracle database 19c on Linux, it may provide some help.