How to create a container database in Oracle 12c

Create an initialization file in your $ORACLE_HOME/dbs folder:

enable_pluggable_database=true
processes=300
control_files="/u02/oradata/cdbveg/control01.ctl","/u03/oradata/cdbveg/control02.ctl"
audit_file_dest="/u01/oracle/admin/cdbveg/adump"
audit_trail=DB
compatible=12.1.0.2
db_block_size=8192
db_domain=""
db_name="cdbveg"
db_recovery_file_dest_size=429496729600
db_recovery_file_dest="/u04/fra"
diagnostic_dest=/u01/oracle
dispatchers="(PROTOCOL=TCP) (SERVICE=cdbvegXDB)"
local_listener = "(ADDRESS = (PROTOCOL=TCP)(HOST=myserver.mydomain.com)(PORT=1521))"
open_cursors=300
remote_login_passwordfile=EXCLUSIVE
undo_tablespace=UNDOTBS1
# use ASMM (Automatic shared memory managaement)
sga_target=2G
sga_max_size=2G
pga_aggregate_target=128M
# Disable AMM (Automatic Memory Managament)
memory_target=0
memory_max_target=0

Create the necessarry directories:

mkdir -p /u02/oradata/cdbveg
mkdir -p /u03/oradata/cdbveg
mkdir -p /u01/oracle/admin/cdbveg/adump
mkdir -p /u02/oradata/cdbveg/seed

Set your environment variables correcly, in my case they were:

export ORACLE_SID=cdbveg
export ORACLE_BASE=/u01/oracle
export ORACLE_HOME=/u01/oracle/product/12102

Start an instance:

sqlplus / as sysdba 
statup nomount

Create your container database:

create database cdbveg
user sys identified by MySecretPasswd
user system identified by MySecretPasswd
logfile group 1(
 '/u02/oradata/cdbveg/red01a.log',
 '/u03/oradata/cdbveg/red01b.log'
) size 128M,
group 2 (
 '/u02/oradata/cdbveg/red02a.log',
 '/u03/oradata/cdbveg/red02b.log'
) size 128M
character set al32utf8 national character set al16utf16
extent management local datafile '/u02/oradata/cdbveg/system01.dbf' size 256M autoextend on next 16M maxsize unlimited
sysaux datafile '/u02/oradata/cdbveg/sysaux01.dbf' size 128M autoextend on next 16M maxsize unlimited
default temporary tablespace temp tempfile '/u02/oradata/cdbveg/temp.dbf' size 256M
undo tablespace undotbs1 datafile '/u02/oradata/cdbveg/undotbs01.dbf' size 256M
enable pluggable database
seed
file_name_convert = ('/u02/oradata/cdbveg','/u02/oradata/cdbveg/seed')
system datafiles size 128M autoextend on next 8M maxsize 2048M
sysaux datafiles size 64M
USER_DATA tablespace users datafile '/u02/oradata/cdbveg/seed/users.dbf' size 128M reuse autoextend on next 32M maxsize unlimited;

The above statement will create a container database, and a seed database which will follow the specifications listed under the keyword "seed" in the create-statement above.
The /u02/oradata/cdbveg/seed directory will contain the datafiles used for future creations of PDBs based on the seed template.
In addition to the mandatory system and sysaux tablespaces, I add a tablespace for user data, too.

Finally, run the necessary scripts:

sqlplus / as sysdba 

SQL> @?/rdbms/admin/catalog.sql
SQL> @?/rdbms/admin/catblock.sql
SQL> @?/rdbms/admin/catproc.sql

SQL> alter session set "_ORACLE_SCRIPT"=false;

SQL> @?/rdbms/admin/catoctk.sql
SQL> @?/rdbms/admin/owminst.plb
SQL> @?/sqlplus/admin/pupbld.sql

Verify creation:

select name,con_id,dbid,open_mode from v$containers

NAME                     CON_ID       DBID OPEN_MODE
-------------------- ---------- ---------- ------------------------------
CDB$ROOT                      1 3469467854 READ WRITE
PDB$SEED                      2  682995139 READ ONLY