[Oracle] ORACLE initialization or shutdown in progress

Problem : ORA-01033: ORACLE initialization or shutdown in progress

==== Error ====
SQL> conn xenia  
Enter password:
ERROR:
ORA-01033: ORACLE initialization or shutdown in progress
Process ID: 0
Session ID: 0 Serial number: 0
Warning: You are no longer connected to ORACLE.

The Oracle is starting or shutdown now , you just need to wait.
then enter the command later.

==== Solution ====

SQL> conn xenia  
Enter password:
ERROR:
ORA-01033: ORACLE initialization or shutdown in progress
Process ID: 0
Session ID: 0 Serial number: 0


Warning: You are no longer connected to ORACLE.
SQL> conn xenia


SQL> 

After waiting for a moment , it's okay to continue.