ORA-00020

ORA-00020: maximum number of processes (%s) exceeded

SQL> show parameter processes

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
processes                            integer     150

SQL> select count(*) from v$process;

  COUNT(*)
----------
       149

SQL> alter system set processes=300 scope=spfile;

System altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> startup
ORACLE instance started.

SQL> show parameter processes

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
processes                            integer     300