Oracle Start up and shutdown in Linux.

Find Oracle Environment variable.

[root@hariere oracle]# env |grep ora
 USER=oracle
 PATH=/usr/kerberos/sbin:/home/oracle/app/oracle/product/11.2.0/dbhome_1/bin:/usr/lib/qt-3.3/bin:/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin
 MAIL=/var/spool/mail/oracle
 PWD=/home/oracle
 LOGNAME=oracle
 ORACLE_HOME=/home/oracle/app/oracle/product/11.2.0/dbhome_1

Connect to oracle user by changing root user to oracle and connect to oracle database.
ora1


















[root@hariere oracle]# su - oracle
$ sqlplus '/ as sysdba'

SQL*Plus: Release 11.2.0.1.0 Production on Sun Mar 29 23:55:40 2015

Copyright (c) 1982, 2009, Oracle. All rights reserved.

Connected to an idle instance.

SQL> 

Start up Oralce database
in this mode database will start and user able to connect database.
SQL> startup
ORACLE instance started.

Total System Global Area 740724736 bytes
Fixed Size 1339092 bytes
Variable Size 461373740 bytes
Database Buffers 272629760 bytes
Redo Buffers 5382144 bytes
Database mounted.

STARTUP NOMOUNT 
startup nomount mode, you can start the insatance and mount a database without opening and allows DBA's to perform maintenance.

STARTUP MOUNT
startup mount mode, you can start the instance , mount and open the database. This is a restricted mode and available only for DBA's
like import export data
upgrade and migrations.


Shutdown database 
  1. Normal Shutdown
  2. Shutdown Immediate
  3. Shutdown Abort

Normal Shutdown
  oracle will wait for all active users to disconnect their sessions. As the parameter name (normal) suggest, use this option to shutdown the database under normal conditions
SQL> shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> 

Shutdown Immediate
 oracle will rollback all active transaction and disconnect all active users. Use this option when there is a problem with your database and you don’t have enough time to request users to log-off.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> 

Shutdown Abort

 all active user sessions will be terminated immediately. Uncommitted transactions will not be rolled back. Use this option only during emergency situations when the “shutdown” and “shutdown immediate” doesn't work.
SQL> shutdown abort
ORACLE instance shut down.
SQL>