ORA-00020: maximum number of processes (150) exceeded

[oracle@dbtest backup]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Thu May 5 13:58:39 2022

Copyright (c) 1982, 2013, Oracle. All rights reserved.

ERROR:
ORA-00020: maximum number of processes (150) exceeded

Enter user-name:
ERROR:
ORA-01017: invalid username/password; logon denied

Enter user-name:
ERROR:
ORA-01017: invalid username/password; logon denied

SP2-0157: unable to CONNECT to ORACLE after 3 attempts, exiting SQL*Plus
[oracle@dbtest backup]$ sqlplus -prelim / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Thu May 5 14:00:48 2022

Copyright (c) 1982, 2013, Oracle. All rights reserved.

SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
ORA-01012: not logged on
Process ID: 0
Session ID: 0 Serial number: 0

SQL> exit
Disconnected from ORACLE
[oracle@dbtest backup]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Thu May 5 14:05:03 2022

Copyright (c) 1982, 2013, Oracle. All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> startup
ORA-01081: cannot start already-running ORACLE - shut it down first
SQL> shutdown immediate;
ORA-01507: database not mounted

ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1.5166E+10 bytes
Fixed Size 2268032 bytes
Variable Size 2248148096 bytes
Database Buffers 1.2885E+10 bytes
Redo Buffers 30375936 bytes
Database mounted.
Database opened.