How to fix the Oracle error ORA-01158: database string already mounted?

In this post, you’ll learn more about the Oracle ErrorORA-01158: database string already mounted with the details on why you receive this error and the possible solution to fix it.

Oracle Error Description

ORA-01158: database string already mounted

Reason for the Error ORA-01158: database string already mounted

Another instance has a database by this name mounted.

How to fix the Error ORA-01158: database string already mounted ?

You can fix this error in Oracle by following the below steps

Find which instance is still running. Perhaps you have not lost the control files after all.