LRM-00101: unknown parameter name '_first_spare_parameter' I am part-way through an upgrade from Oracle 11g to 18c on RedHat.

The Database Upgrade Assistant gives the message:

Errors encountered during the execution of "Database Components Upgrade".

Oracle_Server.log shows:

select count(*) from v$instance
*
ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0
select count(*) from v$instance
*
ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0
LRM-00101: unknown parameter name '_first_spare_parameter'
ORA-01078: failure in processing system parameters
select status from v$instance
*
ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0


How can I resolve the issue LRM-00101: unknown parameter name '_first_spare_parameter'?
From the spfile create a pfile, which can be edited directly:

sqlplus / as sysdba
create pfile='/tmp/pfile.ora' from spfile;
exit


Edit /tmp/pfile.ora, remove _first_spare_parameter. Then create the spfile again:

sqlplus / as sysdba
create spfile from pfile='/tmp/pfile.ora';


Now you can try starting your instance.

Above should work in a standard single instance environment, in a customized or clustered environment you may need extra steps.