安装完oracle，然后执行完下面的自动配置脚本后，没有任何地方设置过密码。

# /etc/init.d/oracledb_ORCLCDB-19c configure

在这个命令执行完成后，会提醒查看完整日志的地方：

Look at the log file “/opt/oracle/cfgtoollogs/dbca/ORCLCDB/ORCLCDB.log” for further details.
Database configuration completed successfully. The passwords were auto generated,
you must change them by connecting to the database using ‘sqlplus / as sysdba’ as the oracle user.

然后执行sqlplus / as sysdba，死活登录不上去，网上各种密码都试过了。查看该日志：/opt/oracle/cfgtoollogs/dbca/ORCLCDB/ORCLCDB.log 上面只有个SID的名字，也没有什么密码信息。。

最后发现别人说了using ‘sqlplus / as sysdba’ as the oracle user。 我一直用的root用户。。su oracle 后就可以了， Enter password 的密码是 change_on_install

[root@localhost dbhome_1]# su oracle
[oracle@localhost dbhome_1]$ sqlplus
SQL*Plus: Release 19.0.0.0.0 - Production on Mon Nov 4 21:42:22 2019
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle.  All rights reserved.
Enter user-name: sys / as sysdba
Enter password: 
Connected to an idle instance.
SQL> 


linux下查看用户：cut -d : -f 1 /etc/passwd
要从root用户切换到oracle用户，然后oracle用户没有密码
然后执行sqlplus，输入sys /as sysdba，没有密码，即可连接上oralce