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The oratab File

Expert Oracle Database Tips by Donald BurlesonMarch 22, 2015

The oratab File

Also see my notes on oraenv.

When the oraenv script is run, it reads the oratab filefound in /etc to determine where the Oracle home for a given database is located.  The oratab file contains entries in the form of ORACLE_SID:ORACLE_HOME:Y, the last character being a Y or N indicating if the database should be started and stopped with the dbstart and dbstop commands, respectively.  Here is a typical oratab entry:

TEST:/u01/app/oracle/product/11.1.0/db_1:Y

Lines beginning with a pound sign (#) in the oratab file are comments.  Valid entries are typically found at the end of the oratab file.

The oratab file can be edited manually using vi or another text editor.  This is often necessary if you the ORACLE_HOMEof a database should be changed.

WARNING:  Never set ORACLE_HOME and ORACLE_BASE variables manually.

Under certain circumstances, it is useful to add an entry to the oratab file that does not refer to a database.  This can allow setting the necessary variables for Oracle without having a database associated with the session.  To do that, follow the format mentioned above to add an entry, making sure to set the last character to N so the dbstart/stop commands do not attempt to start a database that is not there.  This script shows an oratab entry not associated with a database.

11g_db1:/u01/app/oracle/product/11.1.0/db_1:N

A dummy oratab entry like this can be useful on a system that does not yet have a database configured on it or on an Oracle Application Server or a Client install where there may never be a database.

The oratab filetypically contains an entry for each database, but in the current configuration, there is no database set up.  To use the oraenv script, set up a dummy entry in the oratab file.

The oratab file can be edited by the oracle user using vi or another text editor.  Each line in the oratab file has three elements separated by colons.  The first element is the SID, the second indicates the Oracle Home directory for that SID, and the third indicates if the database should be started and stopped by the dbstart/dbshut commands.

Edit the oratab file and add the following line:

db_11g:/u01/app/oracle/product/11.1.0/db_1:N

Though a database does not exist by the name db_11g, this entry allows us to setting up the environment for this home without having to set several variables manually.  Make sure the final element is set to N so Oracle does not attempt to start a database that is not there.

With an entry now in the oratab file, use the oraenv command to set up our environment.  To do that, run .oraenv which causes the oraenv script to be run as part of the current shell rather than as a subprogram.

$ . oraenv
 
ORACLE_SID = [oracle] - db_11g
The Oracle base for ORACLE_HOME=/u01/app/oracle/product/11.1.0/db_1 is /u01/app/oracle
 

$ echo $ORACLE_SID
 
db_11g
 
$ echo $ORACLE_HOME
 
/u01/app/oracle/product/11.1.0/db_1
 
$ echo $PATH
 

/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/home/oracle/bin:/u01/app/
oracle/product/11.1.0/db_1/bin

 
 
 
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