In my organization, I had issues connecting to the database from my local machine, but not from a server
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Additional information: 4376
Additional information: 344321215
Process ID: 0
Session ID: 0 Serial number: 0
http://www.dba-oracle.com/sf_ora_27101_shared_memory_realm_does_not_exist.htm
The reason that local machines seem to get the error connecting to the DB is because the centralized management directory server stores network address tnsping details using SERVICE_NAME still rather than SID, which is preventing local machines/vdi's access to the DB.
This is revealed by comparing tnsping results from local machine vs from server machine.
https://docs.oracle.com/database/121/NETAG/config_concepts.htm#NETAG003
The DBA can fix this configuration in the directory server, or alternatively, reconfigure tnsping details back to SERVICE_NAME.