Setting an Oracle Environment variable – ORACLE_HOME

What is ORACLE_HOME used for?

* The ORACLE_HOME is an environment variable which is used to set and define the path of Oracle Home (server) Directory.
* The ORACLE_HOME directory will have the sub directories, binaries, executables, programs, scripts, etc. for the Oracle Database.
* This directory can be used by any user who wants to use the particular database.
* If the ORACLE_HOME variable is defined as an environment variable, then during the installation process, the Oracle Home Path will be set to the directory defined as default. If the variable is not defined, then the Oracle will take its own default location. i.e. The ORACLE_HOME variable does not have to be preset as an environment variable, it can be set during the installation process.
* Basically The ORACLE_HOME variable is in the following ORACLE_BASE directory:
ORACLE_HOME=$ORACLE_BASE/product/10.2.0.

What is ORACLE_BASE used for?

* The ORACLE_BASE is also an environment variable to define the base/root level directory where you will have the Oracle Database directory tree - ORACLE_HOME defined under the ORACLE_BASE directory.
* Basically, The ORACLE_BASE directory is a higher-level directory, than ORACLE_HOME, that you can use to install the various Oracle Software Products and the same Oracle base directory can be used for more than one installation.

Note: If you did not set the ORACLE_BASE environment variable before starting OUI, the Oracle home directory is created in an app/username/directory on the first existing and writable directory from /u01 through /u09 for UNIX and Linux systems, or on the disk drive with the most available space for Windows systems. If /u01 through /u09 does not exist on the UNIX or Linux system, then the default location is user_home_directory/app/username.

How to check if ORACLE_HOME is set already?

On Unix/Linux Systems:

Basically, before or after the Oracle Database is installed, the oracle user profile, the environment variable file, is prepared where all the required environment variables for Oracle are set. i.e. ORACLE_BASE, ORACLE_HOME, ORACLE_SID,PATH, LD_LIBRARY_PATH, NLS_LANG, etc.

The user profile file can be
.bash_profile – Bash Shell
.profile – Bourne Shell or Korn shell
.login­ – C Shell

Note: This user profile file will be under user’s home directory i.e. $HOME/.bash_profile

To check specific environment variable set:

$ echo $ORACLE_HOME

To check all the environment variables set:

$ env

On Windows Systems:

To check specific environment variable set:

C:\> set ORACLE_HOME

OR

C:\echo %ORACLE_HOME%

To check all the environment variables set:

C:\> set

Or

C:\> env

Other way, to check the ORACLE_HOME, is as follows.

Start -> Run -> Regedit (enter) -> HKEY_LOCAL_MACHINE -> SOFTWARE –> ORACLE

i.e. My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE

How to check using sqlplus command:

To Find the ORACLE_HOME path in Oracle Database
In 9i:

SELECT substr(file_spec,1,instr(file_spec,'lib')-2) ORACLE_HOME FROM dba_libraries
WHERE library_name='DBMS_SUMADV_LIB';

In 10g:

SQL > var OHM varchar2(100);
SQL > EXEC dbms_system.get_env('ORACLE_HOME', :OHM) ;
SQL > PRINT OHM

Linux/Unix:

echo $ORACLE_HOME

Windows:

start - run - regedit (enter) - HKEY_LOCAL_MACHINE - SOFTWARE - ORACLE

Type the below command at prompt if the environment variable is defined for ORACLE_HOME

c:\> set oracle_home (ENTER)


How to set the ORACLE_HOME environment variable?

On Unix/Linux Systems:

Define the ORACLE_HOME value in the user profile file i.e. .bash_profile or .profile

ORACLE_HOME=$ORACLE_BASE/product/10.2.0
export ORACLE_HOME

Source the user profile as follows:

Bash shell:

$ . ./.bash_profile

Bourne shell or Korn shell:

$ . ./.profile

C shell:

% source ./.login

If no profile file is set with environment variables, then physically also be set as follows:

Bourne, Bash, or Korn shell:

$ ORACLE_BASE=/oracle/app
$ export ORACLE_BASE
$ ORACLE_HOME=$ORACLE_BASE/product/10.2.0
$ export ORACLE_HOME

C Shell:

% setenv ORACLE_BASE /oracle/app
% setenv ORACLE_HOME /oracle/app/product/10.2.0

On Windows Systems:

My Computer -> Properties -> Advanced -> Environment Variables -> System Variables -> New/Edit/Delete (to set the variables)

After setting the environment variables as above, open a fresh CMD tool and check whether they set properly or not. Do not try on already opened CMD tool to make sure the variables set or not.

Another way to physically set the variables as follow at the DOS prompt:

C:\> set ORACLE_HOME=C:\oracle\app\product\10.2.0
C:\> echo %ORACLE_HOME%

Note: I would suggest to refer the Oracle Documentation on Installation where these environment variables are discussed and explained with the enough information.