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What is ORATAB and what is it used for?
"oratab" is a file created by Oracle in the /etc or /var/opt/oracle directory when installing database software. It is used to list the databases and software versions installed on a server.
This file may contain comments staring with a pound signs (#) in column one, and data lines consisting of entries in the following format:
database_sid:oracle_home_dir:Y|N
- database_sid is the system id (SID) of an Oracle instances on the server.
- Oracle_home_dir is the ORACLE_HOME directory associated with this instance.
- The Y|N flags indicate if the instance should automatically start at boot time (Y=yes, N=no).
Besides acting as a registry for what databases and software versions are installed on the server, ORATAB is also used for the following purposes:
Oracle's "dbstart" and "dbshut" scripts use this file to figure out which instances are to be start up or shut down (using the third field, Y or N).
The "oraenv" utility uses ORATAB to set the correct environment variables.
One can also write Unix shell scripts that cycle through multiple instances using the information in the oratab file.