Fail to connect to oracle with error startup or shutdown initiating process

- Check initSID.ora files at each folder, at ORACLE_HOME/database/admin or pfile
- reconnect using sqlplus if ora-12514, check environment variable and look at lsnrctl services does service_name is correct re arrange listener.ora put global_dbname at first
- fail during startup with ora-01113 and ora-01110 from sqlplus use recover datafile 'path corrupt data'; then recover database or shutdown database and startup again
- check select status from v$instance; it should be mounted
- ORA-01109 database not open. manual way : alter database open;