Show All online SID Database Oracle 11 in Linux SuSe and Find Database file
cat /etc/oratab

As a DBA, you need to learn the Oracle Data Dictionary.


&quot;One of the most important parts of an Oracle database is its data dictionary, which is a read-only set of tables that provides information about the database&quot;
SQL&gt;select name from v$datafile;




# set environment
. oraenv &lt;&lt;&lt; SID1; 
# login as sys user (IPC)
sqlplus / as sysdba
# list datafiles
SQL&gt;select name from v$datafile;
SQL&gt;exit
# repeat for SID2 and SID3

Side note.
One Oracle Database System (SID) can serve multiple databases (schemas). It is expensive, in terms of resources, to have multiple systems running.
# create database 1
SQL&gt;create user DB_OWNER_1 identified by 'pass';
SQL&gt;create table db_owner_1.t (x char(1));
# create database 2
SQL&gt;create user DB_OWNER_2 identified by 'pass';
SQL&gt;create table db_owner_2.t (x char(1));


# login as 'app user A' who has privileges to manipulate tables (DML) in database 1.
sqlplus appuserA/pass@TNS_ALIAS_1 
SQL&gt;alter session set current_schema = &quot;DB_OWNER_1&quot;
SQL&gt;insert into t values ('x');

# login as 'app user B' who has privileges to manipulate tables (DML) in database 2.
sqlplus appuserB/pass@TNS_ALIAS_2 
SQL&gt;alter session set current_schema = &quot;DB_OWNER_2&quot;
SQL&gt;insert into t values ('x');

You now have two applications operating on two different databases served by the one and same Oracle Database System.
Best of luck!