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Now that the listener is stopped, log in to SQL*Plus as the SYSTEM user using the orcl service name to determine whether you can still connect to the database.

$ sqlplus system@orcl

$ lsnrctl start

$ lsnrctl status

A CDB includes the following components:

Root: The root, named CDB$ROOT, stores Oracle-supplied metadata and common users. An example of metadata is the source code for Oracle-supplied PL/SQL packages. A common user is a database user known in every container. A CDB has exactly one root.
Seed: The seed, named PDB$SEED, is a template that you can use to create new PDBs. You cannot add objects to or modify objects in the seed. A CDB has exactly one seed.
PDBs: A PDB appears to users and applications as if it were a non-CDB. For example, a PDB can contain the data and code required to support a specific application. A PDB is fully backward compatible with Oracle Database releases before Oracle Database 12c.

Each of these components is called a container. Therefore, the root is a container, the seed is a container, and each PDB is a container. Each container has a unique container ID and name within a CDB.

Environment variables

ORACLE_OWNER= oracle

ORACLE_HOME= /scratch/u01/app/oracle/product/19.0.0/dbhome_1

Open a terminal window, execute the oraenv command to set the environment variables and connect to the database orcl.
$ . oraenv

ORACLE_SID = [oracle] ? orcl

The Oracle base has been set to /scratch/u01/app/oracle

Check if the database is a non container database.
select name, cdb, con_id from v$database;

Issue the SQL statement that returns the port that is configured for EM Express.
select instance_name, status, con_id from v$instance;

If a port number is not returned by this statement, then you must manually configure an HTTPS port for this CDB, as described in “Configuring the HTTPs Port”.
select dbms_xdb_config.gethttpsport() from dual;

Display the PDBs

select con_id, name, open_mode from v$pdbs;

ALTER SESSION SET CONTAINER=orclpdb;

alter pluggable database orclpdb open;

SELECT dbms_xdb_config.gethttpsport() from dual;

$ lsnrctl status

SQL> show parameter dispatchers;

exec DBMS_XDB_CONFIG.SETHTTPSPORT(5501);

Oracle Enterprise manager

In your Web browser, enter the URL to access Enterprise Manager: https://hostname:portnumber/em.

Note:Starting with Oracle Database 19c, Oracle EM Express, the default management option for Oracle Database, is based on Java JET technology. Currently, only the Performance menu is available in the 19c JET version. Therefore, we are using the 18c Flash Oracle EM Express in our tutorials. Use the following command to revert to Flash Oracle EM Express:

SQL> @?/rdbms/admin/execemx emx

To return to 19c JET Oracle EM Express, use the following command:

SQL> @?/rdbms/admin/execemx omx

ALTER USER HR ACCOUNT UNLOCK IDENTIFIED BY password;

The system responds:

User altered.

The HR account is unlocked and its password is password.

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