c>sqlplus                                               
 c>user-name:sys as sysdba                                
 c>password:sys 
 sql>show user; 
 sql>COLUMN name FORMAT a20;    
 sql>SELECT * FROM all_users;  
 sql>SELECT * FROM all_users;
 sql>SELECT * FROM user_users;
 sql>show con_name;                                           // to check connection name to make sure you’re in the correct location, type
 sql>show pdbs;                                               // to show pluggable database
 sql>SELECT name, con_id FROM v$pdbs;                         // to get component id of pluggable database
 sql>SELECT name as "Service_name" from v$active_services WHERE con_id =3;  //  to get service name of pluggable database component id
 
 sql>alter pluggable database all open;                   // to open all pluggable database
 sql>alter pluggable database ukapex close;               // to close each pluggable database at all not possible
 
 sql> CREATE PLUGGABLE DATABASE ukapex ADMIN USER ukapexadmin IDENTIFIED BY ukapexadmin;   // to create new pdbs
 sql>show pdbs;                                           // to show pluggable database
 SQL> alter pluggable database ukapex OPEN;                // to open database
 sql>show pdbs;                                           // to show pluggable database
 sql>show con_name;                                           // to check connection name to make sure you’re in the correct location, type
 sql>alter session set container=ukapex;                  // To switch to the ukapex pluggable database,
 sql>show con_name;                                           // to check connection name to make sure you’re in the correct location, type
 SQL> ALTER DATABASE OPEN;                                    // Before creating a new user, you need to change the database to open by executing the following command:
 SQL> CREATE USER dekkoaccount IDENTIFIED BY dekkoaccount;     // to create a new user for creating the sample database in the pluggable database ukapex
 SQL> GRANT CONNECT, RESOURCE, DBA TO dekkoaccount;            // grant privileges to the dekkoaccount user
 SQL> CONNECT dekkoaccount@ukapex;                             //  error:ora-12154: tns: could not resolve the identifier
 
    // set listener  in tnsnames.ora as follows
  ukapex_tns =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = SDI-Uzzal)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = ukapex)
    )
  )
  
  // close command and reconnect 
  cmd> lsnrctl start    // no ;
  cmd>lsnrctl reload
  // again try to connect  
 
 sql>alter pluggable database open;                       // pluggable database already open
 sql>select ora_database_name from dual;                  // to show open database
 sql>select tablespace_name from dba_tablespaces;         // to show table space name
 sql>show parameter sga;    // to check memory use;
 sql>select COMP_ID, STATUS from DBA_REGISTRY            // USER_REGISTRY displays information about the components loaded into the database that are owned by the current user. Column, Datatype, NULL, Description
 sql>select account_status from dba_users   // to all user status
 sql>ALTER USER APEX_LISTENER IDENTIFIED BY listener_user ACCOUNT UNLOCK;   // overwrite previous user and password
 sql>ALTER USER dba_users ACCOUNT UNLOCK;                          // problem
 sql>exit;
 sql>sqlplus
 sql>suer-name: sys as sysdba    // no ;
 sql>password:sys 
 sql>conn hongbao/hongbao@commonpdbs_tns;                // connected
 sql>select account_status from dba_users where username = 'hongbao';   // no row selected 
 sql>select name, open_mode from v$pdbs;                   // plugable database status
 sql>select instance_name from v$instance;                 // show sid

 sql>exit;