How to solve - ORA-00205 I'm trying to create a multitenant database, but I get ORA-00205

I made a directory for datafiles:

[oracle@localhost oradata]$ mkdir -p TESTCDB/data/TESTCDB


I made an initTESTCDB.ora file:

db_name='TESTCDB'
enable_pluggable_database=true
audit_trail='db'
control_files='/u01/app/oracle/oradata/TESTCDB/data/TESTCDB/control01.ctl'
db_block_size=8192
db_domain='' 
memory_target=629145600
memory_max_target=629145600
open_cursors=300
processes=300 
remote_login_passwordfile='EXCLUSIVE'
undo_tablespace='UNDOTBS1'


I set environment variables 

[petar.testDB ~] vi .profile_TESTCDB
#!/bin/sh
umask 022
ORACLE_SID=TESTCDB; export ORACLE_SID
ORACLE_HOME='/u01/app/oracle/product/12.2/db_1'; export ORACLE_HOME
export PATH=$ORACLE_HOME/bin:$PATH


Now, I try to startup database in mount mode and I get this error:

SYS&gt; startup mount
ORACLE instance started.

Total System Global Area  297795584 bytes
Fixed Size          8791960 bytes
Variable Size         234883176 bytes
Database Buffers       50331648 bytes
Redo Buffers            3788800 bytes
ORA-00205: error in identifying control file, check alert log for more info


Thanks in advance.
Petar
Creating a Database with the CREATE DATABASE Statement

If you want to create a database like that, then follow the steps listed on the above link.

Your next step should be Step 8: Start the Instance.

You have not created your the database yet, you do not have a controlfile, so you can not mount it. Startup the instance with nomount, then create the database with CREATE DATABASE.