You can have multiple instances on the same machine, each with their own data files, either sharing the ORACLE_HOME or each with different ORACLE_HOME. ORACLE_HOME and ORACLE_SID are the key environment variables used by Oracle to identify an instance. In addition $ORACLE_HOME/bin must be in your PATH environment variable.
To check the value of these environment variables:
$ env |grep ORACLE
ORACLE_SID=pdb10i1
ORACLE_BASE=/u01/app
ORACLE_HOME=/u01/app/oracle/product/10.2.0
The “oraenv
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