ORA-01090: shutdown in progress - connection is not permitted

 SQL*Plus: Release 12.2.0.1.0 Production on Sun Dec 22 09:16:04 2019

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Enter user-name: sys as sysdba
Enter password:
Connected.
SQL>
SQL>
SQL>
SQL>
SQL> conn sys as sysdba
Enter password:
Connected to an idle instance.
SQL>
SQL>
SQL>
SQL>
SQL> shutdown
ERROR:
ORA-01090: shutdown in progress - connection is not permitted
Process ID: 0
Session ID: 0 Serial number: 0


SQL> startup
ORA-01012: not logged on
Process ID: 0
Session ID: 0 Serial number: 0


SQL> startup force
ORA-01012: not logged on
Process ID: 0
Session ID: 0 Serial number: 0


SQL> shutdown immediate
ERROR:
ORA-01090: shutdown in progress - connection is not permitted
Process ID: 0
Session ID: 0 Serial number: 0


SQL> startup
ORA-01012: not logged on
Process ID: 0
Session ID: 0 Serial number: 0


SQL>  shutdown abort;
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 3170893824 bytes
Fixed Size                  8751840 bytes
Variable Size             922748192 bytes
Database Buffers         2231369728 bytes
Redo Buffers                8024064 bytes
Database mounted.
Database opened.
SQL>