ORA-16006: audit_trail destination incompatible with database open mode

Action: When the Database is opened for read-only access, the audit_trail initialization parameter can only be set to "OS" or "NONE" (FALSE).

SQL> STARTUP MOUNT;
ORACLE instance started.

Database mounted.
SQL> ALTER DATABASE OPEN READ ONLY;
ALTER DATABASE OPEN READ ONLY
*
ERROR at line 1:
ORA-16006: audit_trail destination incompatible with database open mode 


SQL> SHOW PARAMETER AUDIT_TRAIL

============================
audit_trail                   string           DB

SQL> ALTER SYSTEM SET audit_trail=none SCOPE=SPFILE;
System altered.

SQL> SHUTDOWN IMMEDIATE
Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> STARTUP MOUNT
ORACLE instance started.
Database mounted.

SQL> ALTER DATABASE OPEN READ ONLY;
Database altered.