我这里的是dataguard环境,我尝试将从库删除进行重新配置，下面是报错个解决办法:

 

[oracle@18c_single ~]$ dbca -silent -deleteDatabase -sourceDB ora18c
[FATAL] [DBT-10201] Delete database operation cannot be performed.
CAUSE: There are no databases present on the system.

原因：
在/etc/oratab文件中没有数据库的记录信息。
手动在文件中添加数据库的信息即可。
ora18c:/u01/app/oracle/product/18.0.0.0/db_1:N

[oracle@18c_single ~]$ echo $ORACLE_HOME
/u01/app/oracle/product/18.0.0.0/db_1
[oracle@18c_single ~]$ echo $ORACLE_SID
ora18c
[oracle@18c_single ~]$ dbca -silent -deleteDatabase -sourceDB ora18c
Enter SYS user password:

[WARNING] [DBT-19202] The Database Configuration Assistant will delete the Oracle instances and datafiles for your database. All information in the database will be destroyed.
Prepare for db operation
32% complete
Connecting to database
35% complete
39% complete
42% complete
45% complete
48% complete
52% complete
65% complete
Updating network configuration files
68% complete
Deleting instance and datafiles
84% complete
100% complete
Database deletion completed.
Look at the log file "/u01/app/oracle/cfgtoollogs/dbca/ora18c/ora18c5.log" for further details.