ORA-27101: shared memory realm does not exist

Step 1: Log into root user

Step 2: Switch to database tier i.e. oradev in my case

Example: su – oradev

Step 3: Check if Oracle Home and SID is in Order (If incorrect, correct the path using export command)

                Example: echo $ORACLE_HOME

                                   echo $ORACLE_SID

Step 4: login to SYSDBA (Continue to Step 4 if the Home and SID are in order)

                Example: oradev@xxxdevdbsrv:~$ sqlplus / as sysdba

Step 5: Startup Database

                Example:

                               SQL> startup

ORACLE instance started.

Total System Global Area 3207790592 bytes

Fixed Size                  2163592 bytes

Variable Size             469769336 bytes

Database Buffers         2717908992 bytes

Redo Buffers               17948672 bytes

Database mounted.

Database opened.