SQL*Plus

Last tested on Oracle 18.4.0.0.0, CentOS 7.6.1810 (2019-06-21)

Shutdown the database.

$ sqlplus / as sysdba
SQL> SHUTDOWN IMMEDIATE

Start the database.

SQL> STARTUP
SQL> ALTER PLUGGABLE DATABASE ALL OPEN;

Enable automatic shutdown and startup.

$ systemctl daemon-reload
$ systemctl enable oracle-xe-18c

Connect to the database

$ sqlplus system@"chara/XEPDB12"

SQL*Plus: Release 18.0.0.0.0 - Production on Wed Jun 26 15:02:51 2019
Version 18.4.0.0.0

Copyright (c) 1982, 2018, Oracle.  All rights reserved.

ERROR:
ORA-01017: invalid username/password; logon denied


Enter user-name: system
Enter password:
Last Successful login time: Fri Jun 21 2019 23:16:57 -06:00

Connected to:
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0

SQL>