Database Startup

Ensure that the ORACLE_SID variable is correctly set. The database can be started from svrmgrl or on version 8+ from SQLPLUS. Then use one of the following start-up options
STARTUP NOMOUNT
 Starts oracle instance, allocates memory for SGA, starts background processes.
STARTUP MOUNT
 Starts oracle instance and associates it with the database, memory for SGA is then allocated, background processes are initialised and control control files are opened and verified.
STARTUP OPEN
 Starts oracle instance and associates it with the database, memory for SGA is then allocated, background processes are initialised and control control, redo and datafiles files are opened.
Database Shutdown
Ensure that the ORACLE_SID variable is correctly set. The database can be shutdown from svrmgrl or on versions 8+ from SQLPLUS. Then use one of the following shutdown options. The options all achieve the same result. Closing down the database entails closing the database files, redo log files, control files, background processes and finally deallocates memory used for SGA.
SHUTDOWN NORMAL

 Disallows new connections to the database, gracefully waits until the users closes their connections to the database, then finally performs the shutdown of the database.
SHUTDOWN TRANSACTIONAL

 Disallows new connections to the database, it waits unlit the current user transactions are commit or rolled back, and the user connections are then closed. After closing of all current database connections the database is shutdown.
SHUTDOWN IMMEDIATE

 Disables new connections to the database, terminates all current user's connections, making rollback of all uncommitted transactions. The database is then shutdown.
SHUTDOWN ABORT
 This is equivalent to a database crash, new connections to database are disabled , all current user's connections a terminated, does not make a rollback of uncommitted transactions. Database is shutdown instantly.