Here is a reference if I need to start an Oracle database instance. It may not be the best way but this is how I done.
I became the user oracle
root@solaris:/ # su – oracle
Exported the variable that sets the instance that I’ll deal with
oracle@solaris:~ $ export ORACLE_SID=testing
Started sqlplus
oracle@solaris:~ $ sqlplus /nolog
SQL*Plus: Release 9.2.0.8.0 – Production on Fri Jun 18 10:57:30 2010
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected as user sysdba
SQL> connect /as sysdba
Connected to an idle instance.
And finally started the instance
SQL> startup
ORACLE instance started.Total System Global Area 209747872
bytesFixed Size 728992
bytesVariable Size 167772160
bytesDatabase Buffers 40960000
bytesRedo Buffers 286720
bytes
Database mounted.
Database opened.
Pressed CTRL+D to exit sqlplus
SQL> Disconnected from Oracle9i Enterprise Edition Release 9.2.0.8.0 – 64bit Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.8.0 – Production
You’ll also need to start the Oracle Database Listener