Hi,
Sometimes You can get “NID-00121: Database should not be open ” error.
Details of error are as follows.
NID-00121: Database should not be open
Cause: The database was open. To change the DBID, the database must be mounted exclusively.
Action: Shutdown the database and mount it in exclusive mode.
This error is related with the database OPEN state. Shutdown Instance and startup mount mode.
shutdown immediate; startup mount;
and Run nid tool again using the following post.
Do you want to learn Oracle Database for Beginners, then read the following articles.
https://ittutorial.org/oracle-database-19c-tutorials-for-beginners/