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
oracle@solaris:~ $ sqlplus /nolog
SQL*Plus: Release 18.104.22.168.0 – 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
ORACLE instance started.
Total System Global Area 209747872
Fixed Size 728992
Variable Size 167772160
Database Buffers 40960000
Redo Buffers 286720
Pressed CTRL+D to exit sqlplus
SQL> Disconnected from Oracle9i Enterprise Edition Release 22.214.171.124.0 – 64bit Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 126.96.36.199.0 – Production
You’ll also need to start the Oracle Database Listener