Patterns

su to user oracle
sqlplus /nolog
CONNECT sys/password as SYSDBA
SHUTDOWN
SHUTDOWN IMMEDIATE
SHUTDOWN ABORT
STARTUP

Shell scripts to start stop database
$ORACLE_HOME/bin/dbstart
$ORACLE_HOME/bin/dbstop

Oracle Enterprise Manager Database Control
$ORACLE_HOME/bin/emctl stop dbconsole
$ORACLE_HOME/bin/emctl start dbconsole

ORACLE_SID and ORACLE_HOME can be found in /etc/oratab. Format is
$ORACLE_SID:$ORACLE_HOME:AUTOSTART Y/N