ORA-01506: Missing or illegal Database Name, minimum parameters required for Oracle to start an instance

The following experiment process is from 10.2.0.3:
Reference SQL> select * from V $ version;

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Oracle Database 10g Enterprise Edition Release 10.2.0.3.0-Prod
PL/SQL release 10.2.0.3.0-Production
Core 10.2.0.3.0 Production
TNS for Linux: Version 10.2.0.3.0-Production
Nlsrtl version 10.2.0.3.0-Production

We know that the order in which the Oracle startup instance looks for parameter files is spfile <Sid>. ora, spfile. ora, init <Sid>. ora. So what is the minimum parameter for Oracle to start an instance? The following is the experiment process.
Create any name instance
Reference [ora10g @ mcprod ~] $ Export oracle_sid = zhoul

The parameter file initzhoul. ora is required to start the instance.
Reference [ora10g @ mcprod ~] $ Sqlplus "/As sysdba"

SQL * Plus: Release 10.2.0.3.0-production on Sat Jan 9 13:55:35 2010

Copyright (c) 1982,200 6, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup
ORA-01078: Failure in Processing System Parameters
LRM-00109: cocould not open parameter file '/ora10g/Oracle/product/10.2.0/db_1/dbs/initzhoul. ora'
SQL> exit
Disconnected

Create the parameter file initzhoul. ora
Reference [ora10g @ mcprod ~] $ Touch/ora10g/Oracle/product/10.2.0/db_1/dbs/initzhoul. ora

Start again and prompt that the db_name parameter is required
Reference SQL> startup nomount
ORA-01506: Missing or illegal Database Name

Add db_name to the parameter file
Reference [ora10g @ mcprod ~] $ Echo "db_name = zhoul"> initzhoul. ora

Attempt to start zhoul instance again and start successfully
Reference SQL> startup nomount
Oracle instance started.

Total system global area 117440512 bytes
Fixed size 1260384 bytes
Variable Size 58721440 bytes
Database buffers 50331648 bytes
Redo buffers 7127040 bytes

View the data dictionary v $ parameter and find that only db_name is the non-default value to start the instance. That is to say, you only need to set the db_name parameter to start the database instance. Other parameters can use the initial value.
Reference SQL> select name from V $ parameter where isdefault = 'false ';

Name
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Db_name

Observe alert_zhoul.log. We can see that Oracle has adjusted some initial values in the zhoul startup instance. Note that automatic undo retention adjustment is disabled.
Reference SQL> show parameter background_core_dump

Name type value
-----------------------------------------------------------------------------
Background_core_dump string partial

[Ora10g @ mcprod log] $ cat alert_zhoul.log
Sat Jan 9 13:58:08 2010
Adjusting the default value of parameter parallel_max_servers
From 40 to 25 due to the value of parameter Processes (40)
Sat Jan 9 13:58:08 2010
Starting Oracle instance (normal)
License_max_session = 0
License_sessions_warning = 0
Sat Jan 9 13:58:19 2010
Adjusting the default value of parameter parallel_max_servers
From 40 to 25 due to the value of parameter Processes (40)
Sat Jan 9 13:58:19 2010
Starting Oracle instance (normal)
License_max_session = 0
License_sessions_warning = 0
Sat Jan 9 13:59:52 2010
Adjusting the default value of parameter parallel_max_servers
From 40 to 25 due to the value of parameter Processes (40)
Sat Jan 9 13:59:52 2010
Starting Oracle instance (normal)
License_max_session = 0
License_sessions_warning = 0
Sat Jan 9 14:01:25 2010
Adjusting the default value of parameter parallel_max_servers
From 40 to 25 due to the value of parameter Processes (40)
Sat Jan 9 14:01:25 2010
Starting Oracle instance (normal)
License_max_session = 0
License_sessions_warning = 0
Shared memory segment for instance monitoring created
Picked latch-free SCN scheme 2
Using log_archive_dest_1 parameter default value as/ora10g/Oracle/product/10.2.0/db_1/dbs/Arch
AutoTune of Undo retention is turned off.
License_max_users = 0
Sys auditing is disabled
Ksdpec: called for event 13740 prior to event group Initialization
Starting up Oracle RDBMS version: 10.2.0.3.0.
System Parameters with non-default values:
Db_name = zhoul
Pmon started with PID = 2, OS id = 32133
Psp0 started with PID = 3, OS id = 32135
Mman started with PID = 4, OS id = 32137
Dbw0 started with PID = 5, OS id = 32139
Lgwr started with PID = 6, OS id = 32141
Ckpt started with PID = 7, OS id = 32143
SMON started with PID = 8, OS id = 32145
Reco started with PID = 9, OS id = 32147
Mmon started with PID = 10, OS id = 32149
Mmnl started with PID = 11, OS id = 32151 link: http://dbzone.iteye.com/blog/566478